CN113738335A

CN113738335A - Seam control integrated volume fracturing method suitable for massive pure shale oil reservoir

Info

Publication number: CN113738335A
Application number: CN202111033751.XA
Authority: CN
Inventors: 张斌; 杜林麟; 赵广海
Original assignee: Orient Baolin Technology Development Beijing Co ltd
Current assignee: Orient Baolin Technology Development Beijing Co ltd
Priority date: 2021-09-03
Filing date: 2021-09-03
Publication date: 2021-12-03
Anticipated expiration: 2041-09-03
Also published as: CN113738335B

Abstract

The invention provides a seam-control integrated volume fracturing method suitable for a massive pure shale oil reservoir. The method comprises the following steps: performing horizontal section subsection multi-cluster perforation on a target fracturing section of the target horizontal well after completion; then, performing in-section multi-scale fracture expansion through in-section fracturing, pumping acid liquor in the in-section fracturing process, and injecting proppants with different particle sizes to perform full-scale support on the artificial fracture to form a four-level fracture network structure acid-etched micro-fracture-secondary fracture-main fracture full-expansion network structure; wherein, injecting the proppant with different grain sizes to carry out full-scale propping of the artificial fracture comprises the following steps: injecting 70-140 meshes of proppant to prop the microcracks, injecting 40-70 meshes of proppant to prop the secondary cracks and the toe ends of the main cracks, injecting 30-50 meshes of proppant to prop the middle-toe ends of the main cracks, injecting 20-40 meshes of proppant to the near-well ends of the main cracks and filling the near-well-bore zone; wherein, the intrazone fracturing adopts ultra-dense cutting fracturing with the crack cluster spacing smaller than 10 m.

Description

Seam control integrated volume fracturing method suitable for massive pure shale oil reservoir

Technical Field

The invention belongs to the technical field of unconventional petroleum and natural gas yield increase, and particularly relates to a seam control integrated volume fracturing method suitable for a massive pure shale oil reservoir.

Background

In recent years, the quality of a large amount of newly-increased reserves of petroleum is poor, the single-well productivity is low, and the effective development benefit is poor. Chinese continental shale oil has great potential, is found in different degrees in Songliao, quasi-Pascal, Eldos and other basins, and is expected to become a large-scale succession resource. The difference between the Chinese continental shale oil and the North American marine shale oil is large, the single-layer thickness is small, the TOC and S1 values are relatively small, and the non-homogeneous layer of the sweet spot is strong. In recent years, a large amount of work is carried out on shale oil in China, certain achievements are achieved, and the Changqing shale oil and the Jimusala shale oil have great technical breakthroughs and benefit development is achieved.

At present, from the perspective of refining and classifying shale oil, the Changqing shale oil is taken as an example and classified into I-IV reservoirs, which are respectively a multi-phase sand overlapping thick layer type, a thick sand and thin sand and mud interbedded type, a thin sandstone interlayer shale type and a block pure shale type (as shown in figure 1). The shale oil types which have been developed with benefits at present are I type and II type, the main method is large-scale large-sand volume fracturing of a long horizontal well, but the reconstruction difficulty of the shale oil types of III and IV type reservoirs, particularly IV type blocky pure shale type shale oil, is relatively large, and a development mode with stronger adaptability and more effectiveness is still explored.

The massive pure shale oil reservoir reservoirs, namely III and IV reservoir reservoirs are greatly different from I and II reservoir reservoirs, and the mobility of the I and II reservoir reservoirs depends on two points to a great extent: the hydrocarbon reservoir in the shale reservoirs of the I type and the II type is moved to a thick sand layer to form better reservoir, thereby providing good geological conditions for high yield after pressing; the natural fractures of the shale reservoirs of the type I and the type II are developed, the pore connectivity is strong, and the control volume of the fracture reserves can be maximized under the cross action of the volume fracturing fracture network and the natural fractures, so that the high yield after fracturing is facilitated. The III and IV reservoirs have poor congenital conditions and compact reservoirs, oil and gas are mainly stored in pores and holes of the shale, and the pore conditions are poor; from the reservoir space, the isolated pores are dominant, and the connectivity is poor (as shown in fig. 2A-2D); meanwhile, natural fractures do not develop, and based on the inherent characteristics of reservoirs, if a fracturing method of class I and class II shale oil reservoirs is continuously used, a better yield cannot be obtained, which is proved in blocky pure shale reservoirs of Jilin oil fields. Aiming at the special reservoir stratum, innovative ideas are needed, and a fracturing method capable of realizing the benefit development of the massive pure shale oil reservoir is urgently needed at present, the successful key point of the fracturing method is that the aims of maximizing the SRV of the whole horizontal well and complicating a single-section fracture are taken as targets, more shale pores and holes are communicated, and meanwhile, according to the particularity, targeted optimization is carried out, and the increase, storage and production increase are realized.

Disclosure of Invention

The invention aims to provide a reliable fracturing method for benefit development of massive pure shale oil reservoirs. The fracturing method can not only effectively promote the single-section fracture to be complicated, but also maximize the integral SRV (stimulated rock volume) of the horizontal well, simultaneously ensure the long-term effective flow conductivity of a fracture network, finally realize the fracture control volume modification of the massive pure shale oil reservoir on the whole and improve the fracturing effect.

In order to achieve the aim, the invention provides a fracture-control integrated volume fracturing method suitable for a massive pure shale oil reservoir, wherein the method comprises the following steps:

performing horizontal section subsection multi-cluster perforation on a target fracturing section of the target horizontal well after completion;

after horizontal section subsection multi-cluster perforation is carried out on a target horizontal well after well completion, multi-scale crack expansion in sections is carried out through in-section fracturing, acid liquor is pumped in the in-section fracturing process, and propping agents with different particle sizes are injected to carry out full-scale support on artificial cracks, so that a four-stage crack network structure, namely an acid-etched micro-crack-secondary crack-main crack full-expansion network structure (refer to fig. 3), is formed;

wherein, injecting the proppant with different grain sizes to carry out full-scale propping of the artificial fracture comprises the following steps: injecting 70-140 meshes of propping agent to prop the micro-cracks, injecting 40-70 meshes of propping agent to prop the secondary cracks and the toe ends of the main cracks, injecting 30-50 meshes of propping agent to prop the middle-toe ends of the main cracks, injecting 20-40 meshes of propping agent to fill the near-well ends of the main cracks and the near-well zones;

and the intrazone fracturing adopts ultra-dense cutting fracturing with the crack cluster spacing smaller than 10 m.

In the seam-control integrated volume fracturing method suitable for the massive pure shale oil reservoir, the support of the acid-etched micro-seams depends on the rock fragments subjected to acid etching.

The fracture control integrated volume fracturing method suitable for the massive pure shale oil reservoir is characterized in that on the basis of a three-stage fracture network for shale fracture modification, a certain amount of acid liquid is pumped in the fracturing process to further increase the fracture modification volume, and a full-scale fracture network of acid-etched micro-fractures (namely etched fractures) + micro-fractures + secondary fractures + main fractures is formed.

In the seam-control integrated volume fracturing method applicable to the massive pure shale oil reservoir, preferably, in the segmental fracturing process, when the pre-seam is made, the horizontal segment is divided into two types of longitudinal seam expansion promotion and dessert small layer reconstruction based on the longitudinal position relation between the perforation position and the dessert small layer of the reservoir, and different pre-seam making modes are selected; wherein,

the perforation position is not positioned in the small sweet spot layer of the reservoir layer and is divided into a front-end crack expanding mode, the front-end crack forming is carried out in a front-end high-viscosity liquid crack forming mode, and the crack is longitudinally expanded to the sweet spot layer, so that the aims of communicating the small sweet spot layer and reforming the small sweet spot layer are fulfilled; preferably, the viscosity of the highly viscous liquid is not less than 100mpa · s;

the perforation position is positioned in the dessert small layer and is divided into dessert small layer reconstruction, the low-mucus body front-arranged seam construction is adopted, the longitudinal excessive expansion of the seam can be controlled by the low-mucus body seam construction characteristic, and the dessert small layer is precisely reconstructed in a scalpel mode; preferably, the low viscosity liquid has a viscosity of not higher than 30 mpa-s;

due to the fact that the blocky shale is in page development, the conventional low-viscosity liquid cannot well expand the crack height, and the optimal implementation mode selects a proper front crack forming mode according to different types, so that the requirement of crack seam height expansion in the blocky shale can be better met.

In the above fracture-control integrated volume fracturing method suitable for the massive pure shale oil reservoir, preferably, the type of the proppant is selected by combining the reservoir characteristics, and the precoated sand proppant is selected from the plastic stratum. In the aspect of selection of the type of the proppant, the reservoir characteristics can be closely combined, the fracture resistance and the embedding resistance of the proppant are mainly considered, the plastic characteristics of the reservoir are particularly required to be noticed, in a partial plastic stratum, the embedding degree of the proppant is high, and the precoated sand can be preferably used for reducing the embedding degree of the proppant and ensuring the long-term conductivity of a fracture network. Taking a Songliao green section block-shaped pure shale oil reservoir as an example, the reservoir is partially plastic, the conventional proppant is seriously embedded, and the fracturing modification is suitable for adopting precoated sand to improve the fracturing effectiveness and the long-term stability.

In the above seam-controlled integrated volume fracturing method suitable for the massive pure shale oil reservoir, preferably, a temporary plugging material is added in the process of carrying out ultra-dense cutting fracturing to plug the transformed clusters; the device is used for increasing the pressure in a shaft, forcing the opening of an unmodified perforation cluster and turning liquid, thereby realizing uniform modification among clusters;

more preferably, the temporary plugging material is added in the fracturing process to perform temporary plugging steering in an in-layer temporary plugging steering mode, an interlayer temporary plugging steering mode and an in-layer temporary plugging steering mode;

the temporary plugging diversion in the layer can be realized by temporarily plugging the middle and far-end cracks by delivering the temporary plugging agent in the fracturing process, so that the complication of the middle and far-end cracks is promoted; the interlayer steering can be realized by a mode of delivering a temporary plugging agent to block a near-well main crack and a perforation hole in the fracturing process, so that the integral cracks among clusters are complicated;

the supporting ultra-dense cutting fracturing technology, because the number of horizontal segment perforation clusters is large, in order to save the operation cost, a single segment of fracturing contains a plurality of clusters of perforations, generally 4-10 clusters, and the heterogeneity of a reservoir stratum can cause the heterogeneity of reconstruction among clusters; aiming at the problem, temporary plugging materials can be added in the fracturing process to plug the reformed clusters, the pressure in a shaft is increased, the non-reformed perforation clusters are forced to be opened, and liquid is diverted, so that the uniform reforming among clusters is realized. It is worth mentioning that the temporary plugging steering can be divided into intra-layer temporary plugging steering and inter-layer temporary plugging steering, the intra-layer temporary plugging steering mainly aims at achieving steering of middle and far end cracks, more complication of middle and far section cracks can be achieved, and the inter-layer temporary plugging steering mainly achieves uniform reconstruction among clusters; aiming at the requirements of massive pure shale oil reservoirs on maximization and complication of an integral fracture network, the modes of in-layer temporary plugging steering, interlayer temporary plugging steering and in-layer temporary plugging steering can better achieve the aim of fracturing transformation, communicate isolated pores and holes more and achieve the aim of increasing the benefit.

In the above fracture-control integrated volume fracturing method suitable for the massive pure shale oil reservoir, preferably, a polymer clean multifunctional fracturing fluid is used in the fracturing process;

the conventional fracturing at home and abroad usually adopts guanidine gum to prepare fracturing fluid, but the residue rate is high, generally 30-40%, and the residue after gum breaking can block effective pores and has obvious damage to a reservoir stratum; in order to better meet the requirement of reservoir protection of blocky shale, a polymer clean multifunctional fracturing fluid system is researched and developed, the fracturing fluid system is mainly prepared by replacing guar gum with a polymer thickening agent or a modified polymer thickening agent, multiple functions can be realized, low concentration is slick water, medium concentration is linear gum, a cross-linking agent is added to form jelly, and basic liquid properties such as viscosity and the like can meet construction requirements.

Reservoir protection is always an important content in the research of fracturing technology, the rock-mineral characteristics and the storage characteristics of the blocky shale determine that the reservoir protection work in the fracturing process is more important, and the reservoir protection needs to be further strengthened on the basis of a conventional shale oil reservoir; through relevant statistics of domestic blocky shale, during the expansion prevention experiment process of pure shale reservoir stratum coring, a rock core can be burst by self-absorption water without an expansion prevention agent, and the water sensitivity is extremely high; from the production perspective, the productivity of individual wells in a block decreases rapidly after fracturing, even the productivity decreases to 0, and the blockage of a fracturing channel caused by clay expansion is an important reason; therefore, the joint control integrated volume fracturing method suitable for the massive pure shale oil reservoir is matched, and the operation of well protecting the reservoir of the massive shale is very important; based on the above, the preferable technical proposal of the anti-swelling, anti-sticking and polymer cleaning multifunctional fracturing fluid is provided.

In the above seam-control integrated volume fracturing method suitable for the massive pure shale oil reservoir, preferably, in the in-section fracturing process, an anti-swelling and adhesion-fixing agent is used for anti-swelling and adhesion-fixing;

more preferably, in the in-zone fracturing process, an anti-expansion and viscosity-fixing agent is added into the injected drilling fluid, so that the anti-expansion and viscosity-fixing agent is used for anti-expansion and viscosity-fixing;

the damage of clay minerals is mainly divided into two types, one type is blockage caused by water absorption expansion, and the other type is blockage caused by the migration of clay particles;

in order to solve the problem of clay damage, through the research and development of anti-swelling and anti-sticking technologies such as raw material optimization, material proportion optimization, preparation process optimization, a large number of indoor anti-swelling and anti-sticking experiments and the like, the clay can be solidified while being prevented from swelling, and the purpose of reservoir protection is achieved; the preferable anti-swelling and viscosity-fixing agent can be a low-molecular biopolymer, can prevent clay swelling and particle migration, can control the hydration reaction of cationic particles in the clay by the internal polymer structure, can not change the lattice of the clay, can effectively inhibit the migration of clay particles with minimum size, can not damage stratum, and has good compatibility with fracturing fluid.

In the above fracture-control integrated volume fracturing method suitable for the massive pure shale oil reservoir, preferably, in the staged fracturing process, the shale is changed from oleophilic to hydrophilic by using a wetting improver;

more preferably, in the staged fracturing process, a wetting improver is added into the injected drilling fluid, so that the shale is changed from oleophilic to hydrophilic by using the wetting improver;

in one embodiment, the wetting improver is a nonionic polyether surfactant wetting improver;

the massive pure shale oil reservoir crude oil is stored in isolated pores and holes, and how to effectively replace the crude oil out of the pores is a key factor for increasing yield; from the view point of wettability, the massive pure shale has strong oleophylic characteristics and is not beneficial to oil-water replacement. In order to better solve the problem, the shale is changed from strong oleophylic state to hydrophilic state by using a wetting improver, so that wetting inversion is realized, oil-water replacement is facilitated, the yield after pressing is increased, and the recovery ratio is increased; through a large amount of researches, the selected nonionic polyether surfactant wetting improver can better realize the wetting inversion of the shale. The innate properties of the bulk pure shale determine the high performance requirements for the wettability-improving agent:

A. the pore is small, and the wetting improver needs to be capable of entering;

B. a large amount of surface areas formed by acid etching micro-cracks-micro cracks-secondary cracks in the four-level network structure are positioned in the depths of the cracks, and the wetting improver has the remote characteristic and can fully improve the wettability of the remote shale;

C. the oil is required to be fully washed, the oil is effectively washed, the emulsification phenomenon is avoided, and meanwhile, the washed oil drops are required to be small in particle size and easy to separate out from pores.

The wetting improver adopted by the preferred technical scheme can effectively meet the high-performance requirement of blocky pure shale on the wetting improver.

In the above fracture-control integrated volume fracturing method suitable for the massive pure shale oil reservoir, preferably, the target fracturing section of the target horizontal well is determined by the following method: before fracturing, carrying out reservoir compressibility evaluation of a target well, determining a fractured dessert and further determining a target fracturing section;

more preferably, before fracturing, performing a reservoir compressibility evaluation of the target well, and determining a fractured dessert includes:

A. acquiring logging information, and determining rock compressibility based on the logging information so as to determine an engineering dessert;

in a specific embodiment, the rock compressibility comprises one or a combination of two or more of young's modulus, poisson's ratio, total rock brittleness, internal friction angle, horizontal stress difference coefficient, fracture toughness value and density;

the pressability screening standards of the engineering desserts in different oil fields and among blocks are different, and the corresponding engineering desserts are selected according to the dividing requirements of the engineering desserts in different blocks of different oil fields;

B. determining the physical properties of the reservoir, and further determining a geological dessert;

wherein the reservoir physical properties preferably include porosity, permeability, oil and gas saturation and natural fracture development;

the geological dessert reservoir physical property screening standards of different oil fields and blocks are different, and the geological dessert is determined according to the dividing standards of the geological dessert of different blocks of different oil fields;

C. combining the engineered dessert with the geological dessert, and initially fracturing the dessert sections;

comprehensively considering rock compressibility and reservoir physical properties, and primarily determining a fractured dessert section;

D. and further screening the initially determined fractured dessert section, removing the section with poor well cementation quality in the initially determined fractured dessert section, and taking the rest section as a final fractured dessert section.

In the above fracture-control integrated volume fracturing method suitable for the massive pure shale oil reservoir, preferably, the clustering perforation position of the horizontal segment segmented multi-cluster perforation is determined by the following steps:

A. analyzing and calculating a fracture induction force field and a ground stress difference value in a section (as shown in figure 4), and determining a perforation cluster interval range which is beneficial to the maximization of the transformed volume after pressing and the formation of a complex fracture network on the basis of a fracture induction force field and a ground stress difference value screen;

the in-stage analysis and calculation of the fracture inducing force field and the ground stress difference value can be carried out by a conventional mode (for example, the in-stage analysis and calculation can be carried out by using the existing fracturing simulation software and the ground stress simulation software), and theoretically, when the fracture inducing force field is consistent with the ground stress difference value, the maximum transformation volume and the formation of a complex fracture network are most beneficial to the maximization after the fracturing;

B. based on the perforation cluster spacing range determined in the step A, avoiding the position of a casing collar, and finally determining the clustered perforation positions in each section by combining the determined positions of the fractured dessert sections;

the oil fracturing of the I-type shale and the II-type shale has better physical property conditions, the cluster spacing is 15-30m on the whole domestic at present, better fracturing effect can be achieved, the massive shale has poor congenital conditions, the cluster spacing needs to be further optimized, more cracks can communicate with isolated pores and hole structures of the massive shale in a fine, dense and multi-cluster mode, and therefore the yield is better released.

In the seam-controlled integrated volume fracturing method applicable to the massive pure shale oil reservoir, preferably, the number of each cluster of perforations of the horizontal-segment segmented multi-cluster perforation is determined by an optimization mode of limit current-limiting perforation parameters;

more preferably, the number of perforations per cluster of the horizontal segment segmented multiple cluster perforation is determined by a method comprising the following steps: :

A. simulating to obtain the influence factors of the number of clusters, the cluster spacing and the number of perforation holes on the uniform opening of the holes and the uniform extension of cracks;

simulating to obtain influence factors of the number of clusters, the cluster spacing and the number of perforation holes on uniform opening of the holes and uniform extension of the cracks by adopting a conventional mode in the field, for example, simulating by using a gohfer isoquizzling software to obtain the influence factors of the number of clusters, the cluster spacing and the number of perforation holes on uniform opening of the holes and uniform extension of the cracks;

B. based on the influence factors of the cluster number, the cluster spacing and the perforation hole number on the uniform opening of the holes and the uniform extension of the cracks, the number of holes in each cluster is obtained through fitting calculation in combination with parameters such as fluid viscosity, construction displacement, reservoir thickness, rock mechanics parameters, hole size and cluster spacing;

the quantity of each cluster of holes is obtained through fitting calculation by using a conventional mode in the field, for example, the quantity of each cluster of holes is obtained through fitting calculation by using close cutting current-limiting fracturing optimization design software such as gohfer and fracpro PT;

on the basis of conventional shale oil density cutting clustering perforation (12-20 holes/cluster), perforation hole density and perforation number are further optimized, a limit current limiting concept is introduced, optimal perforation parameters are obtained through numerical simulation and special software calculation, perforation hole density is optimized to be 4-8 holes/cluster, auxiliary processes such as temporary plugging steering and the like are matched, perforation opening rate is greatly improved, perforation opening rate is comprehensively evaluated and improved by 35%, and the method has important significance for benefit development of pure shale oil.

The invention provides a fracture-control integrated volume fracturing method for a massive pure shale oil reservoir, which is based on the multi-angle aspects of fracture promotion complication, maximization of integral SRV modification of a horizontal well and fracture effectiveness control, and comprises the following steps:

the massive pure shale oil reservoir stratum has the characteristics of insufficient innate conditions, poor pore conditions and poor connectivity, so the crack-control integrated volume fracturing method suitable for the massive pure shale oil reservoir provided by the invention firstly realizes maximization of a fracture network in a section through multi-scale crack expansion in the section so as to communicate isolated pores as much as possible. The mineral components of the blocky pure shale are greatly different from region to region, but in general, a large amount of acid-soluble minerals such as dolomite, calcite, siderite and the like exist, and acid liquor can form acid-etched earthworm holes and etched micro-cracks in the stratum. On the basis of transforming a three-level fracture network by class I and class II shale fracturing, a certain amount of acid liquid is pumped in the fracturing process to further increase the fracture transformation volume to form a full-scale fracture network of acid-etched micro-fractures (namely etching fractures) + micro-fractures + secondary fractures + main fractures, and meanwhile, residual acid has a cleaning effect on a flow guide channel of a proppant after fracturing, so that the flow guide capacity of the fractures can be further enhanced.

From the perspective of staged fracturing of the horizontal well, the SRV maximization of the fracture is closely related to the yield after fracturing. The biggest difference between shale oil and a conventional low-permeability reservoir is that a stronger starting pressure gradient exists, the starting pressure gradient enables seepage of a shale oil reservoir matrix to exist in different flowing areas, and effective reduction of non-flowing areas between fractures is the key point for realizing the SRV maximization of horizontal well fractures. Aiming at the problem, in the seam-control integrated volume fracturing method suitable for the massive pure shale oil reservoir, provided by the invention, an ultra-dense cutting fracturing technology is used. The fracture diversion form is different from that of the conventional shale oil fracturing fracture network + natural fracture intersection, the block-shaped shale is mainly used for providing diversion capability for the fracturing fracture network after being pressed, in the aspect of fracture spacing, the fracture spacing needs to be further reduced, and a reservoir body is chopped in an ultra-dense cutting mode, so that the horizontal section is effectively utilized, a non-flow area is reduced, linear flow and quasi-linear flow wave and volume are enhanced, the SRV of the horizontal section is maximized, and the transformation effect is improved.

The pore radius of massive pure shale is small, and the wettability of shale is oleophilic, so that even if a fracture network is formed, crude oil cannot flow into a fracture from a pore hole; aiming at the difficult problem, the fracture control integrated volume fracturing method suitable for the massive pure shale oil reservoir provided by the invention adopts a wetting inversion means to realize effective control of the fracture.

The seam-controlled integrated volume fracturing method suitable for the massive pure shale oil reservoir provided by the invention not only can effectively promote the complication of single-section fractures, but also can maximize the integral SRV of the horizontal well, and simultaneously can ensure the long-term effective flow conductivity of a fracture network, thereby finally realizing the seam-controlled volume transformation of the massive pure shale oil reservoir on the whole and improving the fracturing effect.

Drawings

FIG. 1 is a schematic diagram of a refined classification of shale oil.

Fig. 2A is a schematic diagram of a block 2120.19m buried block pure shale pore throat ball-and-stick model and a gap connectivity model.

Fig. 2B is a schematic diagram of a block 2401.57m buried block pure shale pore throat ball-and-stick model and a gap connectivity model.

Fig. 2C is a schematic diagram of a pore-throat ball-and-stick model and a gap connectivity model of a block 2100.36m buried deep-striped long-grained quartz shale.

Fig. 2D is a schematic diagram of a pore-throat ball-and-stick model and a gap connectivity model of a block 2378.83m buried deep-striped long-grained quartz shale.

FIG. 3 is a schematic diagram of a four-stage fracture network structure.

FIG. 4 is a diagram illustrating the in-segment analysis of crack-induced force field and the difference between the ground stress and the induced force field.

FIG. 5 is a schematic diagram of the formation properties of the GY1 well horizontal well path in example 1.

FIG. 6 is the horizontal section log data and stress profile of GY1 well in example 1.

Fig. 7A is a schematic diagram of scale optimization in example 1.

Fig. 7B is a schematic diagram of displacement optimization in embodiment 1.

FIG. 8 is a schematic view of the horizontal well-fracture-control integrated volume fracturing of GY1 well in example 1.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be described in detail and completely with reference to the drawings in the embodiments of the present invention. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The invention provides a seam-control integrated volume fracturing method suitable for a massive pure shale oil reservoir, which comprises the following steps:

In the embodiment of the seam-control integrated volume fracturing method applicable to the massive pure shale oil reservoir, the support of the acid-etched micro-seams depends on the rock fragments subjected to acid etching.

The embodiment of the seam-control integrated volume fracturing method suitable for the massive pure shale oil reservoir is that on the basis of a three-level fracture network transformed by shale fracturing, a certain amount of acid liquid is pumped in the fracturing process to further increase the fracture transformation volume and form a full-scale fracture network of acid-etched micro-fractures (namely etched fractures) + micro-fractures + secondary fractures + main fractures.

Further, in the process of in-segment fracturing, when pre-crack forming is carried out, the horizontal segment is divided into two types of longitudinal crack expansion promotion and dessert small layer modification based on the longitudinal position relation between the perforation position and the dessert small layer of the reservoir, and different pre-crack forming modes are selected; wherein,

the perforation position is not positioned in the small sweet spot layer of the reservoir layer and is divided into a front-end crack expanding mode, the front-end crack forming is carried out in a front-end high-viscosity liquid crack forming mode, and the crack is longitudinally expanded to the sweet spot layer, so that the aims of communicating the small sweet spot layer and reforming the small sweet spot layer are fulfilled; wherein the viscosity of the highly viscous liquid is preferably not less than 100mpa · s;

the perforation position is positioned in the dessert small layer and is divided into dessert small layer reconstruction, the low-mucus body front-arranged seam construction is adopted, the longitudinal excessive expansion of the seam can be controlled by the low-mucus body seam construction characteristic, and the dessert small layer is precisely reconstructed in a scalpel mode; wherein the viscosity of the low mucus body is preferably not higher than 30mpa · s;

Furthermore, the type of the proppant is selected according to the characteristics of the reservoir, and the coated sand proppant is selected from the plastic stratum. In the aspect of selection of the type of the proppant, the reservoir characteristics can be closely combined, the fracture resistance and the embedding resistance of the proppant are mainly considered, the plastic characteristics of the reservoir are particularly required to be noticed, in a partial plastic stratum, the embedding degree of the proppant is high, and the precoated sand can be preferably used for reducing the embedding degree of the proppant and ensuring the long-term conductivity of a fracture network. Taking a Songliao green section block-shaped pure shale oil reservoir as an example, the reservoir is partially plastic, the conventional proppant is seriously embedded, and the fracturing modification is suitable for adopting precoated sand to improve the fracturing effectiveness and the long-term stability.

Further, temporary plugging materials are added in the process of carrying out ultra-dense cutting and fracturing to plug the modified clusters; the device is used for increasing the pressure in a shaft, forcing the opening of an unmodified perforation cluster and turning liquid, thereby realizing uniform modification among clusters;

furthermore, in the fracturing process, temporary plugging materials are added to perform temporary plugging steering in an in-layer temporary plugging steering mode, an interlayer temporary plugging steering mode and an in-layer temporary plugging steering mode;

Further, a polymer is used for cleaning the multifunctional fracturing fluid in the fracturing process;

Further, in the in-stage fracturing process, an anti-swelling and anti-sticking agent is used for anti-swelling and anti-sticking;

furthermore, in the staged fracturing process, an anti-expansion and adhesion-fixing agent is added into the injected drilling fluid, so that the anti-expansion and adhesion-fixing agent is used for anti-expansion and adhesion-fixing;

Further, in the staged fracturing process, a wetting improver is used to convert the shale from oleophilic to hydrophilic;

furthermore, in the process of the intra-stage fracturing, a wetting improver is added into the injected drilling fluid, so that the shale is changed from oleophylic to hydrophilic by using the wetting improver;

for example, the wetting improver is a nonionic polyether surfactant wetting improver;

A. the pore is small, and the wetting improver needs to be capable of entering;

Further, the target fracture section of the target horizontal well is determined by: before fracturing, carrying out reservoir compressibility evaluation of a target well, determining a fractured dessert and further determining a target fracturing section;

further, before fracturing, performing a target well reservoir compressibility evaluation, and determining a fractured dessert includes:

Further, the clustering perforation position of the horizontal segment segmentation multi-cluster perforation is determined by the following steps:

Example 1

The embodiment provides a seam-control integrated volume fracturing method suitable for a massive pure shale oil reservoir, which is used for performing volume fracturing on a GY1 well;

GY1 well located in the North of Songliao basin and distributed in great an-heaven zone, having favorable area 3700km²The resource amount is 34.7 hundred million tons, the TOC content is 2-5%, the pressure coefficient is 1.2-1.3, the average quartz content of pure shale of the Qingshan Kou group is 24.0%, the clay mineral content is 49.08%, the Yimeng mixed layer is mainly used, the reservoir brittleness is small, the pore connectivity is poor, and the fracturing transformation difficulty is large.

Referring to fig. 5, the horizontal section of the GY1 well is 1562 meters long, the track of the horizontal well mainly passes through a pure shale section of the Mount Qingshan group, and the X-diffraction experimental analysis of the core well of the Mount Qingshan group shows that the average quartz content is 35.9%, the average clay mineral content is 35.6%, the average feldspar content is 17.7% and the average carbonate content is 10.8%; generally, the content of brittle minerals of the shale reservoir is about 40 percent on average, the brittleness index of the shale reservoir is 39.2-41.5 percent, and the stress difference is 2-4 MPa.

The seam control integrated volume fracturing method suitable for the massive pure shale oil reservoir provided by the embodiment specifically comprises the following steps:

1. carrying out reservoir compressibility evaluation on the GY1 well, determining a fractured sweet spot section, and further determining a target fractured horizontal section; specifically comprises

A. Acquiring logging information, and determining rock compressibility through rock mechanics calculation based on the logging information, so as to preferably select engineering desserts with good compressibility in intervals;

among them, rock compressibility includes young's modulus, poisson's ratio, total rock brittleness (brittleness index), vertical stress, maximum principal stress, minimum principal stress, stress difference, and fracture pressure, and the results are shown in fig. 6;

B. determining reservoir physical properties including porosity, permeability, oil and gas saturation and natural fracture development, and determining a geological dessert by combining geological opinions;

C. comprehensively evaluating the compressibility of the rock and the physical properties of the reservoir layer: combining the engineered dessert with the geological dessert, and initially fracturing the dessert sections;

D. and further screening the initially determined fractured dessert section, removing the section with poor well cementation quality in the initially determined fractured dessert section, and taking the rest section as a final fractured dessert section to further determine a target fractured horizontal section.

2. Optimizing the cluster spacing of the perforation clusters of the target fracturing horizontal segment to determine the clustered perforation positions in each segment; the method specifically comprises the following steps:

A. calculating by using meyer fracturing analysis software, calculating the size of a fracture induced stress field under the condition of analyzing different cluster spacings in sections, combining the calculated reservoir main stress difference value of 2-4MPa, optimally selecting the size of the fracture induced stress field formed by the cluster spacings of 2-4MPa, and finally selecting the cluster spacings of 6-8 m;

B. based on the perforation cluster spacing range determined in the step A, avoiding the position of a casing collar, and finally determining the clustered perforation positions in each section by combining the positions of the fractured dessert sections;

3. optimizing limit current-limiting perforation parameters to determine the number of each cluster of holes; the method specifically comprises the following steps:

4-6 clusters are obtained through calculation, the cluster spacing is 6-8m, the uniform expansion degree of the crack is maximum under the condition of 8-10 holes/cluster, and the influence factor is 1;

B. and calculating geological parameters of the reservoir and the like into a horizontal section stress profile by using software such as MEYER and the like, and determining the perforation position based on the determined parameters such as cluster number, cluster spacing, cluster perforation number and the like.

4. Optimizing the fracturing scale and the displacement;

referring to fig. 7A-7B, MEYER, GHOFER, FRACPRO PT software is used to perform simulation optimization without scale and with different construction displacement, and the most suitable scale and displacement are selected according to the obtained crack propagation form, crack conductivity, and the like.

5. Performing horizontal segment segmented multi-cluster perforation on a horizontal segment of the GY1 well according to the cluster perforation positions and the number of holes in each cluster determined in the steps 2 and 3;

6. the GYI well after segmented multi-cluster perforation is subjected to intra-segment multi-scale fracture expansion through intra-segment fracturing according to the fractured dessert segment determined in the step 2, acid liquid (earth acid) is pumped in the intra-segment fracturing process, and proppants with different particle sizes are injected in a particle size combination mode of multiple proppants to carry out full-scale support on the artificial fractures, so that a four-stage fracture network structure, namely an acid-etched micro-fracture-secondary fracture-main fracture full-expansion network structure is formed; the fracturing adopts a super-dense cutting fracturing mode with a plurality of clusters in a section and short cluster spacing;

wherein 70-140 meshes of propping agent is injected to prop the microcracks, 40-70 meshes of propping agent is injected to prop the secondary fractures and the toe ends of the main fractures, 30-50 meshes of propping agent is injected to prop the middle-toe ends of the main fractures, 20-40 meshes of propping agent is injected to the near-well ends of the main fractures and fills the near-well bore zone;

in the segmental fracturing process, when pre-crack making is carried out, the horizontal segment is divided into two types of longitudinal crack expansion promotion and dessert small layer modification based on the longitudinal position relation between the perforation position and the dessert small layer of the reservoir, and different pre-crack making modes are selected; wherein,

the perforation position is not positioned on a small sweet spot layer of a reservoir layer and is divided into a mode of promoting longitudinal seam expansion, a front high-viscosity liquid seam making mode is adopted for front seam making, a polymer clean multifunctional fracturing fluid system is selected for the case, in the front liquid stage, when the front seam making is carried out in the high-viscosity liquid seam making mode, a thickening agent and a cross-linking agent are used for enabling the liquid viscosity to reach 120mpa & s, and the high-viscosity liquid seam promoting with the viscosity of 120mpa & s is adopted for promoting the longitudinal crack to be communicated to the sweet spot layer, so that the purposes of improving the small sweet spot layer and the small sweet spot layer are achieved;

the perforation position is located in a dessert small layer and is divided into dessert small layer reconstruction, the low-viscosity liquid is arranged in front to carry out seam making, the longitudinal excessive expansion of a crack is controlled, the dessert small layer is precisely reconstructed in a scalpel mode, a polymer clean multifunctional fracturing fluid system is selected in this case, and in the liquid preparation stage, when the low-viscosity liquid is used for carrying out seam making in front, the viscosity of the fracturing fluid is controlled to be less than 30mpa & s in a single thickening agent mode;

putting temporary plugging material layer temporary plugging steering, interlayer temporary plugging steering and in-layer temporary plugging steering mode temporary plugging steering in the process of ultra-dense cutting fracturing to plug the transformed cluster; the device is used for increasing the pressure in a shaft, forcing the opening of an unmodified perforation cluster and turning liquid, thereby realizing uniform modification among clusters;

in the embodiment, the switching of the temporary plugging in the stratum is realized by temporarily plugging the middle and far-end cracks by delivering the temporary plugging agent in the fracturing process, and the switching between the stratums is realized by blocking the main cracks and perforation holes close to the well by delivering the temporary plugging agent in the fracturing process;

taking the third stage of fracturing construction of this embodiment as an example, 190 square of sand is added to the third stage as a whole, 200kg of temporary plugging agent material is added when the sand is added to 50 square, so as to complicate the far-stage cracks in the cracks, and 500kg of temporary plugging agent material is added when the sand is added to 100 square, so as to plug the transformed clusters, force the liquid to turn to the non-pressed clusters, promote the transformation uniformity among the clusters in the stage, and expand the expansion degree of the fractured cracks as a whole.

In the fracturing process, polymer cleaning multifunctional fracturing fluid is used, and polymer thickening agents (polyacrylamide with the molecular weight of about 300 ten thousand) or polymer thickening agents (polyacrylamide with the molecular weight of about 300 ten thousand) + cross-linking agents (organic ketone) with different proportions are added according to different viscosity requirements so as to meet the viscosity requirements; in order to achieve the effect of anti-swelling and anti-sticking, an anti-swelling and anti-sticking agent (about 100 ten thousand polyacrylamide) is added into the fracturing fluid; adding a wetting improver (quaternary ammonium salt) into the shale wetting reversal fracturing fluid for realizing the shale wetting reversal fracturing fluid; for example, the polymer clean multifunctional fracturing fluid used in a certain stage comprises 0.3% of a polymer thickening agent (about 300 ten thousand molecular weight of polyacrylamide), 0.2% of a cross-linking agent (organic ketone), 0.15% of an added anti-swelling and viscosity-fixing agent (about 100 ten thousand of polyacrylamide) and a wetting improver (quaternary ammonium salt) and the balance of water, wherein the total mass of the polymer clean multifunctional fracturing fluid is 100%.

GY1 well construction totaling 35 segments of 138 clusters, total liquid weight 82314 formula, propping agent 3063 formula, total acid injection 352 formula and liquid CO₂3475 tons, 25 times for interlayer temporary plugging process, 3 times for intra-seam temporary plugging process, and 30 sections for fiber sand consolidation process; a schematic diagram of the GY1 well horizontal well seam control integrated volume fracturing is shown in fig. 8.

The microseism result shows that the GY1 well has uniform crack distribution through the crack-control integrated volume fracturing aiming at the massive pure shale oil reservoir, and the ESRV exceeds the design expectation, so that a better effect is achieved. And (3) after the pressure is released, the yield is obtained, the daily yield of shale oil reaches 45 square/day, the daily yield of associated natural gas reaches 2-3 ten thousand square/day, and the major breakthrough of the fracturing of the massive pure shale oil reservoir is obtained.

The principle and the implementation mode of the invention are explained by applying specific embodiments in the invention, and the description of the embodiments is only used for helping to understand the method and the core idea of the invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, there may be variations in the specific embodiments and the application scope, and in summary, the content of the present specification should not be construed as a limitation to the present invention.

Claims

1. A seam-control integrated volume fracturing method suitable for massive pure shale oil reservoirs comprises the following steps:

after horizontal-section segmented multi-cluster perforation is carried out on a target fracturing section of a target horizontal well after well completion, multi-scale crack expansion in the section is carried out through intra-section fracturing, acid liquid is pumped in the intra-section fracturing process, and propping agents with different particle sizes are injected to carry out full-scale support on artificial cracks, so that a four-level crack network structure, namely an acid-etched micro-crack-secondary crack-main crack fully-expanded network structure is formed; wherein, the full-scale propping of the artificial fracture by injecting the propping agents with different particle sizes comprises the following steps: injecting 70-140 meshes of proppant to prop the microcracks, injecting 40-70 meshes of proppant to prop the secondary cracks and the toe ends of the main cracks, injecting 30-50 meshes of proppant to prop the middle-toe ends of the main cracks, injecting 20-40 meshes of proppant to the near-well ends of the main cracks and filling the near-well-bore zone;

wherein, the intrazone fracturing adopts ultra-dense cutting fracturing with the crack cluster spacing smaller than 10 m.

2. The volume fracturing method of claim 1, wherein in the segmental fracturing process, when pre-crack formation is carried out, the horizontal segment is divided into two types of longitudinal crack expansion promotion and dessert small layer reconstruction based on the longitudinal position relation between the perforation position and the dessert small layer of the reservoir, and different pre-crack formation modes are selected; wherein,

the perforation position is not positioned in a small sweet spot layer of the reservoir and is divided into a plurality of pre-arranged seams which are used for promoting longitudinal seam expansion, and the pre-arranged seams are formed in a pre-arranged high-viscosity liquid seam forming mode to promote the longitudinal expansion of the seams to the sweet spot layer;

the perforation position is positioned in the dessert small layer and divided into transformation in the dessert small layer, and the preposed low-viscosity liquid is adopted for making seams.

3. The volume fracturing method of claim 2,

in the process of making a seam by adopting the preposed high-viscosity liquid, the viscosity of the used high-viscosity liquid is not lower than 100mpa & s;

in the process of making the seam by adopting the preposed low-viscosity liquid, the viscosity of the low-viscosity liquid used is not higher than 30mpa & s.

4. The volume fracturing method of claim 1, wherein the temporary plugging material is introduced during the in-zone fracturing, the reformed clusters are plugged, and the temporary plugging diversion is performed.

5. The volume fracturing method of claim 4, wherein the temporary plugging material is put into the fracturing process to perform temporary plugging diversion in an intralayer temporary plugging diversion + interlayer temporary plugging diversion + temporary plugging diversion mode in the layer.

6. The volume fracturing method of claim 1, wherein in the in-zone fracturing process, an anti-swelling and anti-sticking agent is used for anti-swelling and anti-sticking;

preferably, in the in-zone fracturing process, an anti-expansion and viscosity-fixing agent is added into the injected drilling fluid.

7. The volume fracturing method of claim 1, wherein in the staged fracturing process, a wettability-improving agent is used to convert the shale from oleophilic to hydrophilic;

preferably, a wetting improver is added to the injected drilling fluid during the staged fracturing process.

8. The volumetric fracturing method of claim 1, wherein the target fracture segment of the target horizontal well is determined by: before fracturing, carrying out reservoir compressibility evaluation of a target well, determining a fractured dessert section, and further determining a target fractured section;

preferably, the step of developing a target well reservoir compressibility evaluation and determining a fractured sweet spot section comprises:

C. combining the engineering dessert with the geological dessert, and initially setting the engineering dessert as a fractured dessert section;

9. The volumetric fracturing method of claim 8, wherein the clustered perforation locations of the horizontal segment segmented multi-cluster perforations are determined by a method comprising:

A. analyzing and calculating a fracture induction force field and a ground stress difference value in a section, and determining a perforation cluster interval range which is beneficial to the maximization of the transformed volume after pressing and the formation of a complex fracture network based on the comparison of the fracture induction force field and the ground stress difference value;

B. and B, based on the perforation cluster spacing range determined in the step A, avoiding the position of a casing collar, and finally determining the clustered perforation positions in the sections by combining the determined positions of the fractured dessert sections.

10. The volumetric fracturing method of claim 1 wherein the number of perforations per cluster of horizontal segment segmented multi-cluster perforations is determined by a method comprising:

B. based on the influence factors of the cluster number, the cluster spacing and the perforation number on the uniform opening of the perforation and the uniform extension of the crack, the number of the perforations in each cluster is obtained through fitting calculation by combining the fluid viscosity, the construction displacement, the reservoir thickness, the rock mechanics parameters, the perforation size and the cluster spacing parameters.