CN115680591B - Chemical flooding three-dimensional fracturing process suitable for thin and thick oil layers to be distributed alternately - Google Patents
Chemical flooding three-dimensional fracturing process suitable for thin and thick oil layers to be distributed alternately Download PDFInfo
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Abstract
The invention relates to a chemical flooding three-dimensional fracturing process suitable for thin and thick oil layers to be distributed alternately. Comprises the following steps: the whole design method comprises the following steps: the method adopts a staged design, and is used for planning to reform various oil layers in steps, and balancing the injection and production capacity of thin and thick oil layers, wherein the three main aspects comprise well selection, layer selection and construction scale; the design method of the local multi-well group comprises the following steps: the local multi-well group design method is based on a staged design strategy, and is characterized in that when a plurality of well groups with approximate dynamic and static characteristics appear in a block connection, on the basis of the original single injection well design, a single well design is expanded into a multi-well synchronous design by combining dynamic development indexes and dynamic monitoring indexes, geological design synchronous construction design is carried out, a fracturing target layer is combined, and the connection well group is used as a whole for fracturing transformation. The three-dimensional fracturing technology advances the transformation time of a thin oil layer or transforms the thin oil layer and a thick oil layer synchronously; the thin oil layer with different thickness is used to realize the relative synchronous use of the thin oil layer in peak period.
Description
Technical field:
The invention relates to the technical field of oil extraction in oil fields, in particular to a chemical flooding three-dimensional fracturing process suitable for thin and thick oil layers to be distributed alternately.
The background technology is as follows:
In the development process of large-scale land sandstone oil reservoirs, when chemical flooding development is carried out, the fracturing design method is that a single injection and production well is designed, the injection well is selected to reach the standard of less than 70% of injection allocation, the production well is selected to take effect degree as standard, preferably a well with large liquid production and water-containing amplitude reduction and amplitude reduction, the fracturing thick layer is mainly used in the initial stage and the peak stage of blank, injection and main slug, and the mining thin difference layer is mainly used in the later stage of main slug.
In the development process of large-scale land sandstone oil reservoirs, when chemical flooding development is carried out, a single injection and production well is designed, the injection well is selected by taking top pressure allowance as a standard below 70% of injection allocation, the production well is selected by taking the effect degree as a standard, preferably a well with larger liquid production and water content reduction, the single thick layer is mainly fractured in the initial stage and the peak stage of blank, injection and main slug, and the thin difference layer is mainly dug in the later stage of main slug. The original method has better promotion effect on river sand and main sand with the grain size of more than 1m, the utilization ratio reaches more than 85%, and the recovery ratio is improved by more than 16%.
Along with the continuous progress and the deep development of the oil field, development objects become worse gradually, the oil layer span is large, and the oil reservoir characteristics of thin and thick oil layer interaction distribution are formed. The span of the oil layer of the chemical flooding development object is about 50m, which is 2 times of that of the original similar development object. The reserve ratio of the oil layer below 1m is over 50%, the thickness ratio is over 50% and the number ratio is over 80%. The original design method has poor reconstruction effect on the thin difference oil layer below 1m, and the use ratio is only 40%. The method is characterized in that the method is calculated according to a recovery ratio formula E R＝Ev﹡ED (E R -recovery ratio, ev-sweep coefficient, E D -displacement efficiency), the sweep coefficient is approximately taken as a utilization ratio, and the utilization ratio of an oil layer below 1m needs to be more than 70 percent to achieve the aim of improving the overall recovery ratio by 16 percent, so that the prior art cannot meet the requirements.
The invention comprises the following steps:
The invention aims to overcome the problems in the background technology and provides a chemical flooding three-dimensional fracturing process suitable for thin and thick oil layers to be distributed interactively. The chemical flooding three-dimensional fracturing process suitable for the thin and thick oil layer interaction distribution controls the displacement of the classified oil layer, realizes the relatively balanced use degree of the thin and thick oil layer, ensures that the use proportion of the thin and thick oil layer below 1m reaches more than 70%, and achieves the purpose that the chemical flooding of the oil reservoir with the thin and thick oil layer interaction distribution improves the recovery ratio by more than 16%.
The invention solves the problems by the following technical proposal: the chemical flooding three-dimensional fracturing process suitable for thin and thick oil layers in an interactive distribution mode comprises the following two methods:
The whole design method comprises the following steps:
The chemical flooding development process is divided into a plurality of stages according to the injection condition, the development process is designed in stages by an overall design method, various oil layers are planned to be modified in steps, and the injection and production capacities of thin and thick oil layers are balanced, wherein the method comprises three main aspects of well selection, layer selection and construction scale:
a well selection method comprises the following steps: widening the well selection range of the improved injection well, wherein part of the stages mainly improve the injection well, part of the stages synchronously reform the injection well, and part of the stages mainly improve the production well;
b, selecting a layer method: selecting layers by layer selecting sequence and layer section combination; in the aspect of layer sequence selection, the transformation time of a thin difference layer is advanced, or the thin difference layer and a thick oil layer are synchronously transformed; in the aspect of layer segment combination, adopting a permeability level difference method to perform layer segment combination;
C in terms of construction scale: calculating a target layer comprehensive index by using common parameters, and designing a construction scale by using the target layer comprehensive index to ensure that all the modified oil layer developments reach the highest extraction degree under the optimal penetration ratio;
the design method of the local multi-well group comprises the following steps:
The local multi-well group design method is based on a staged design strategy, and is characterized in that when a plurality of well groups with approximate dynamic and static characteristics appear in a block connection, on the basis of the original single injection well design, a single well design is expanded into a multi-well synchronous design by combining dynamic development indexes and dynamic monitoring indexes, geological design synchronous construction design is carried out, a fracturing target layer is combined, and the connection well group is used as a whole for fracturing transformation.
Further, the chemical flooding development process is divided into seven stages according to injection conditions: ① Blank water injection stage; ② A pre-slug injection stage; ③ A primary slug initial stage; ④ A main slug peak period; ⑤ A main slug later stage; ⑥ A sub-slug injection stage; ⑦ And transferring to the subsequent water injection stage.
Further, the specific method for widening the well selection range of the improved injection well comprises the following steps: three types of injection wells are added at stage ①②③: ① The injection allocation is completed by more than 70 percent, and the allowable injection pressure difference is within 1 Mpa; ② The injection profile is unbalanced, and the single small layer inhalation proportion exceeds 30%; ③ The injection-recovery ratio is below 0.8, and the injection intensity is 20% lower than the average level of the whole region; fracturing the extraction well with synchronous effect while adding three injection wells in the first three stages in the ④ th stage; and excavating residual oil potential in the ⑤⑥ th stage, and fracturing the produced wells with accumulated oil production per unit thickness being more than 50% lower than the average level of the block.
Furthermore, in the specific method for widening the well selection range, the extraction end can be matched with the same horizon of the injection end to carry out synchronous reconstruction; according to the concrete method for excavating the potential of the residual oil, the injection well can be synchronously reformed by matching with the same horizon of the extraction end.
Further, the specific method for improving the thin differential layer or synchronously improving the thick oil layer is as follows: the thin differential layer is preferably modified first in stage ①②③; synchronously reforming a thin oil layer and a thick oil layer in the ④ th stage; the ⑤⑥ th stage is not modified by a thick oil layer;
in the case of interval combination, the interval combination is performed using a permeability level difference method.
Further, the method for carrying out interval combination by the permeability level difference method comprises the following steps: the interlayer contradiction is relieved by segmentation, so that cracks are relatively uniformly distributed in an oil layer; increasing the number of fracturing sections of the whole well and the number of layers of the reconstruction purpose; the permeability level difference in the fracturing section is within 20% of the permeability level difference of the present well; when the permeability level difference method is used, the level difference range is narrowed as the highest permeability of the objective layer is increased: when the highest permeability is below 70 millidarcy, the in-segment level difference has smaller influence; when the highest permeability is 70-200 millidarcy, the range of the level difference in the fracturing section is kept within 1-2; when the highest permeability is higher than 200 millidarcies, the intra-fracture zone differential size ranges from 1 to 1.2.
Further, the method for calculating the target layer comprehensive index comprises the following steps: calculating average sandstone thickness, average effective thickness, average permeability and communication direction number according to the layers by taking the target layer as a center; classifying the calculation results, multiplying the classification results by corresponding coefficients respectively, and summing to obtain a target comprehensive index; according to the method for selecting the construction scale of the target layer, the construction scale is selected according to the comprehensive index of the target layer, different construction scales can generate different crack radiuses, and the different crack radiuses correspond to different crack penetration ratios and extraction degrees, that is, the best construction scale corresponds to the highest extraction degree; when different requirements of multiple well groups in multiple directions are balanced on a plane, the total penetration ratio of the optimal directions of all well point planes is required to be not higher than 35%, so that the problem of block water content caused by sudden flooding can be effectively avoided when the two stages are developed.
Further, the local multi-well group design method specifically comprises the following steps:
Step 1: determining a transformation range and the number of wells according to dynamic development indexes, wherein the requirements relate to not less than 4 adjacent well groups, and changing the original single well group analysis into multi-well group analysis; the reference dynamic development index is that more than 80% of indexes in the well selection range are lower than 80% of the average level of the whole area, and the number of the transformed wells in the range reaches more than 70%;
Step 2: according to the dynamic monitoring index, well monitoring and other dynamic and static data which are easily acquired by an oil field are utilized to carry out multi-well synchronous geology and scale design on the same deposition plan; the method aims at guiding scale design by using development geological data, and meeting the development geological requirements through the scale design;
Step 3: and combining the fracturing target layers, and further reducing the range of the range by a refined permeability step difference method to reduce the number of small layers in the fracturing layer section to 2-3 layers.
Further, the method for synchronously geological and scale designing of multiple wells in the step 2 comprises the steps of radiating from a central well of a first well group at the side to a communicating well, then radiating to a plurality of communicating wells according to the well row divergence design where the central well is located, determining well point targets one by one, and simultaneously performing scale designing.
Furthermore, the principle of determining the well point target is a differential principle, and the general monitoring data shows that the differential proportion is lower than 25% of the total well, or the standard range is 20-30% according to the actual situation of the block.
Compared with the background technology, the chemical flooding three-dimensional fracturing technology suitable for thin and thick oil layer interaction distribution has the following beneficial effects:
(1) Compared with the original method, the method has stronger strategic thinking by adopting the whole design method. The overall planning and orderly arrangement of the well selection, the layer selection and the scale of the block are tactical means, which is more beneficial to improving the pertinence of the block development and reducing blindness.
(2) Compared with the original method, the method has the advantages that the reconstruction range is enlarged, the action area of measure reconstruction is increased, the effect is obviously better than that of the original single well design, and the effect is ideal for solving the problem of local difficult injection and difficult production in the peak period of the main slug.
(3) The reconstruction time of the thin difference layer is advanced, and the repeated construction rate of the injection well can be reduced.
(4) The permeability level difference method is adopted, so that the number of the fracturing sections of the whole well can be increased, the number of the fracturing sections of the whole well is increased from 3.5 to 6.5, the number of layers of the reconstruction purpose is increased, the number of layers of the purpose is increased from 7 to 13, and the injection condition of more thin difference layers is improved.
(5) After the well selection range is widened, the water absorption capacity of the thin difference layer can be further enhanced by improving the three types of wells, the interlayer contradiction is relieved, and the overall injection strength of the block is improved.
(6) The interval combination is carried out by adopting the permeability level difference method, so that the interlayer contradiction can be relieved by segmentation, the bad results generated by the dominant channels can be lightened in the fracturing process, and the cracks are relatively uniformly distributed in the oil layer.
(7) In terms of construction scale, the fracturing scale of the Bao Houyou layers of the produced well is optimized in the peak period of the main slug, the single-layer scale of the first three stages is gradually decreased by 20-30%, and the lowest single-layer scale is not lower than 4m < 3 >; the single layer size of the last two stages is gradually increased by 20-30%, and the maximum is not higher than 25m 3. The design can lead the crack to reach the highest single-layer extraction degree along with the extension of the crack to the optimal penetration ratio at the development stage to the peak stage.
(8) The thin difference layer is added as a transformation object in the peak period of the main slug, the long, good and bad pressure cracks of the whole well are controlled, transformation is balanced, the thin and thick oil layers respectively reach the optimal crack penetration ratio and the highest extraction degree, and the production potential of the thin and thick oil layers is synchronously exerted.
The three-dimensional fracturing design process is implemented on the site chemical flooding development block of the Sanan development area, and the actual water content and the actual extraction degree are higher than the digital-analog level.
The three-dimensional fracturing design process block is implemented on the site chemical flooding development block of the Sanan development area, the oil layer utilization ratio below 1m reaches 77.8%, the block stage extraction degree reaches 19.3%, and the recovery ratio is improved by 16.26%.
Description of the drawings:
FIG. 1 is a graph of the recovery ratio of a test zone according to an embodiment of the present invention;
FIG. 2 is a graph showing the comparison of enhanced recovery ratio for the same PV for the test zone of the present invention;
FIG. 3 is a contour diagram of the effective thickness of a test zone according to an embodiment of the present invention; (test area in black frame)
FIG. 4 is a graph showing permeability contours of a test zone according to an embodiment of the present invention; (test area in black frame)
FIG. 5 is a single layer plan view of a test zone according to an embodiment of the present invention.
The specific embodiment is as follows:
Various exemplary embodiments, features, etc. aspects of the present disclosure will be described in detail below with reference to the drawings.
The invention relates to a design method for chemical flooding three-dimensional fracturing of a thin and thick oil layer interactive distribution oil reservoir, which is divided into two layers of an overall design method and a local multi-well group design method.
Integral design method
The chemical flooding development process is divided into the following seven stages according to the injection condition: ① Blank water injection stage ② leading slug injection stage ③ main slug initial stage ④ main slug peak stage ⑤ main slug later stage ⑥ secondary slug injection stage ⑦ to subsequent water injection stage. The whole design method adopts the development process to design in stages, so that various oil layers are planned to be modified in steps, and the injection and production capacities of thin and thick oil layers are balanced, wherein the three main aspects comprise well selection and layer selection and construction scale;
Well selection method A
The concrete method for widening the well selection range of the improved injection well comprises the following steps: three types of injection wells are added at stage ①②③: ① The injection allocation is completed by more than 70 percent, and the allowable injection pressure difference is within 1 Mpa; ② The injection profile is unbalanced, and the single small layer inhalation proportion exceeds 30%; ③ The injection rate is below 0.8, and the injection intensity is 20% lower than the average level of the whole region. And fracturing the extraction well with synchronous effect while adding three injection wells in the first three stages in the ④ th stage. And excavating residual oil potential in the ⑤⑥ th stage, and fracturing the produced wells with accumulated oil production per unit thickness being more than 50% lower than the average level of the block. This stage is controlled by engineering and other factors, and the actual well number ratio is lower than 5%.
B layer selection method
In the aspect of selecting the layer sequence, the original method is changed to change the sequence of changing the thick layer and the thin layer, so that the change time of the thin layer is advanced or the thick oil layer is synchronously changed. The specific method comprises the following steps: the thin differential layer is preferably modified first in stage ①②③; synchronously reforming a thin oil layer and a thick oil layer in the ④ th stage; the ⑤⑥ stage is not modified by a thick oil layer.
In the case of interval combination, the interval combination is performed using a permeability level difference method. The extending direction of the crack is easier to deviate from the stratum with higher permeability and better communication, so that the in-section permeability level difference has higher influence on the trend of the crack, the greater the level difference is, the more the interlayer contradiction is prominent, the more the crack is easy to open in the dominant direction, and the balanced exploitation of other oil layers is not facilitated. The method is that the permeability level difference in the fracturing section is within 20% of the permeability level difference of the well, except that the permeability level difference is influenced by engineering factors such as an interlayer and the like. When the permeability level difference method is used, the level difference range is narrowed as the highest permeability of the objective layer is increased. When the highest permeability is below 70 millidarcy, the in-segment level difference has smaller influence; when the highest permeability is 70-200 millidarcy, the range of the level difference in the fracturing section is kept within 1-2; when the highest permeability is higher than 200 millidarcies, the intra-fracture zone differential size ranges from 1 to 1.2.
The method relieves the interlayer contradiction by sections, is beneficial to relieving bad results generated by the dominant channels in the fracturing process, and ensures that cracks are relatively uniformly distributed in an oil layer. The permeability level difference method is adopted, so that the number of the fracturing sections of the whole well can be increased, the number of the fracturing sections of the whole well is increased from 3.5 to 6.5, the number of layers of the reconstruction purpose is increased, the number of layers of the purpose is increased from 7 to 13, and the injection condition of more thin difference layers is improved. It should be noted that when the number of combined intervals exceeds the current construction limit, the reconstruction can be performed in batches, but the layer selection order is still kept consistent with the whole area.
C construction scale
The construction scale is an important component of the fracturing design method, the construction scale is reasonable, and the oil reservoir can be efficiently developed due to scientific scale design. The original design scheme is used for separating geological design and construction design, the design scale and the oil layer matching degree are low, so that some target layers are not improved enough, and some target layers are excessively improved.
By calculating the comprehensive index of the target layer and matching with the optimal construction scale, the geological design and the construction design are effectively combined, the effective rate of the target layer transformation is improved, and therefore all development layers reach the highest extraction degree. The method for calculating the comprehensive index of the target layer comprises the following steps: calculating average sandstone thickness, average effective thickness, average permeability and communication direction number according to the layers by taking the target layer as a center; and taking the value of the calculation result according to the range, multiplying the value coefficient and the experience weight respectively, and then summing to obtain the target comprehensive index. And (3) utilizing a construction design template to correspond the comprehensive indexes of the target layer to the construction scale, and respectively optimizing the fracturing scale of the Bao Houyou layers of the production well in the peak period of the main slug. The single layer scale of the first three stages is gradually decreased by 20-30%, and the lowest single layer scale is not lower than 4m 3; the single layer size of the last two stages is gradually increased by 20-30%, and the maximum is not higher than 25m 3.
The design can lead the crack to reach the highest single-layer extraction degree along with the extension of the crack to the optimal penetration ratio at the development stage to the peak stage.
The main slug peak period is the key period of fracturing promotion of a production well, and based on the original design, a thin difference layer is added as a transformation object, the comprehensive index of a target layer is calculated (see table 1 as a target layer reference comprehensive index calculation template), and the construction scale is matched according to the index (table 2 is the construction scale under the target layer reference comprehensive index). By calculation, the fracturing scale is optimized in a layering mode, the single seam scale of a thin differential oil layer is improved, and the single seam scale of a thick oil layer is controlled. The production potential of the thin and thick oil layer is synchronously exerted by controlling the length, the difference and the depth of the whole well fracture and balancing transformation, wherein the thin and thick oil layer respectively achieves the optimal fracture penetration ratio and the highest extraction degree.
The comprehensive index calculation formula in table 1 is:
p＝h1*0.55+h2*0.5+q*0.45+n*0.4；
wherein: p purpose layer comprehensive index; h1 average sandstone thickness coefficient; h2 average effective thickness coefficient; q average permeability coefficient; n is a communication coefficient; 0.55, 0.5, 0.45, 0.4 are empirical weight values.
The construction scale calculation formula in table 2 is: v=pi R 2 h; t=r/well spacing;
Wherein: r is the radius of the crack; h is the width of the crack, and the value is 4mm; the well distance is the distance between the injection well and the production well;
TABLE 1
Note that: because of different development blocks, coefficients and index calculation methods are different, and reference is made to empirical algorithms of developed similar blocks. The calculation formula of the comprehensive index in the table is p=h1×0.55+h2×0.5+q×0.45+n×0.4
TABLE 2
Note that: the optimal penetration ratio in the table 1 changes along with the injection and production well spacing; 2 the construction scale is influenced by the comprehensive index and changes along with the injection stage
(II) local multi-well group design method
The local multi-well group design method is an important component of the overall design method, and is based on a staged design strategy, when a plurality of well groups with approximate dynamic and static characteristics appear in a block joint, on the basis of the original single injection well design, the single well design is expanded into a multi-well synchronous design by combining dynamic development indexes and dynamic monitoring indexes, the geological design is synchronously constructed and designed, a fracturing target layer is combined, and the joint well group is integrally subjected to fracturing transformation.
Compared with the original method, the design method of the local multi-well group expands the reconstruction range, increases the action area of measure reconstruction, has obviously better effect than the original single-well design, and has ideal effect on solving the problem of local difficult injection and difficult production in the peak period of the main slug. The design steps are as follows:
Step one: and determining the reconstruction range and the well number according to the requirement, wherein the number of adjacent well groups is not less than 4, and the original single well group analysis is changed into multi-well group analysis. And referring to dynamic development indexes, the indexes of which the range is more than 80 percent and the indexes of which the range is less than 80 percent of the average level of the whole area are referred, and the number of the transformed wells in the range is more than 70 percent.
Step two: and (3) carrying out multi-well synchronous geology and scale design on the same sedimentary plan by utilizing well monitoring and other dynamic and static data which are easy to acquire in the oil field. The method aims at guiding scale design by using development geological data, and meeting the development geological requirements through the scale design. The method is that the well point targets are determined one by one and simultaneously the scale design is carried out from the central well of the first well group at the side part to the communicating wells, then the communication wells are divergently designed according to the well row where the central well is located, and then the communication wells are radiated to a plurality of communicating wells. The principle of determining the target is that the motion difference is generally lower than 25%, and the motion difference can be determined as the motion difference, or the standard range can be 20-30% according to the actual situation of the block. When different requirements of multiple well groups in multiple directions are balanced on a plane, the total penetration ratio of the optimal directions of all well point planes is required to be not higher than 35%, so that the problem of block water content caused by sudden flooding can be effectively avoided when the two stages are developed. The well point design scale can be referred to in tables 1 and 2. The improvement effectiveness of the thin difference layer is facilitated, and the stage utilization degree of the thin difference layer is improved.
Step three: the fracturing target layers are combined, the range of the range is further reduced by a refined permeability level difference method, even a single thin difference layer can be singly pressed, and the pertinence of oil layer transformation below 1m is improved.
Example 1
In order to make the purposes, technical schemes and advantages of the present invention more clear, the following will take a process of applying the present invention to the implementation of a chemical flooding three-dimensional fracturing process of thin and thick oil layer interaction distribution as an example for a certain ternary composite flooding block in a san-an-developing region, and the embodiments of the present invention will be further described in detail with reference to the accompanying drawings.
The ternary composite flooding block is provided with an effective thickness of 7.9m, a permeability of 220mD and a common development well 271, wherein the injection well 161 is provided with a production well 110. The injection and production well spacing is 125m, and the five-point method area well screen cloth well is used for oil production. Wherein, the number proportion of oil layers below 1m is 83.1%, and the thickness proportion is 52.8%.
The specific implementation process of the chemical flooding three-dimensional fracturing process suitable for thin and thick oil layer interaction distribution in a certain ternary composite flooding block application comprises the following steps:
Application of the overall design: after expanding the well selection conditions, adding 25 injection wells for fracturing modification, wherein the part of the wells are divided into three types, and the ① ports are used for completing injection allocation by more than 70%, so that the injection pressure difference is allowed to be within 1 Mpa; ② The injection profile of the 5 ports is unbalanced, and the suction proportion of a single small layer exceeds 30%; ③ The injection intensity is lower than 20% of the average level of the whole region under the injection ratio of 0.8 at 9 ports. And (3) accumulating 85 times of fracturing injection wells, fracturing 680 target layers, wherein the average single-layer thickness is 0.9m, and the average single-layer sand adding amount is 9.0m 3. Wherein, the target layer below 1m is more than 70%, the average single layer thickness is 0.5m, and the average single layer sand adding amount is 12m 3.
Compared with the original design, the fracturing proportion of the injection well is improved by 15.5%, the single-layer thickness of the target layer is reduced by 59%, the number of layers of the fracturing target layer is increased by 46%, and the single-layer sand adding amount is increased by 50%.
TABLE 3 Table 3
The fracturing effect comparison of the method disclosed by the invention and the existing design method is shown in Table 3, and the fracturing effect comparison of the table 3 before and after fracturing shows that the fracturing object of the original design method is a thick oil layer of more than 1m, the fracturing object of the three-dimensional fracturing design method is a thin difference layer of less than 1m, the permeability of the fracturing object is lower than that of the fracturing object, the sand adding amount of a single layer is larger, the depressurization amplitude is relatively smaller, the daily injection increasing level of a single well is equivalent (Table 3), and the application achieves a better effect. The oil layer below 1m was used to increase to 77.8% (Table 4), and the recovery was increased by 16.26%. The oil layer classification and utilization conditions after the three-dimensional fracturing design are shown in Table 4.
TABLE 4 Table 4
| <1m | 1-2m | >2m | Totalizing | |
| Blank water drive | 48.3 | 54.3 | 61.4 | 52.4 |
| Front slug | 75 | 77.7 | 97.5 | 77.2 |
| Ternary main slug | 77.8 | 87.8 | 100 | 82.2 |
The reconstruction time of the thin difference layer is advanced, and the repeated construction rate of the injection well is reduced. Statistics of the number of stage fracturing wells are shown in table 5, after the stage ③④ fracturing, the repeated fracturing proportion in the peak period reaches 50%, after the blank water flooding stage fracturing, the repeated fracturing proportion in the peak period is 34.3%, and the repeated construction rate is reduced by 15.7 percentage points (table 5).
TABLE 5
The three-element block recovery ratio curve of the test area in the embodiment is shown in fig. 1, wherein the third curve from top to bottom is the actual water content of the block, and the water content value is lower than that of the second simulation curve from top to bottom; the third curve from bottom to top is the actual extraction degree curve of the block, and the extraction degree value is higher than that of the second simulation curve from bottom to top. The test zone of this example compares the enhanced recovery ratio pair at the same PV as shown in fig. 2; the uppermost first curve represents the block implementing the three-dimensional fracturing design process of the present invention, which has the highest enhanced recovery. The three-dimensional fracturing design process block is implemented on the site chemical flooding development block of the Sanan development area, the oil layer utilization ratio below 1m reaches 77.8%, the block stage extraction degree reaches 19.3% (shown in figure 2), and the recovery ratio is improved by 16.26% (shown in figure 1).
(II) application of local multi-well group design:
step 1: and determining 10 adjacent groups centering on the oil well as test areas, wherein the total number of the 10 injection wells is 18, and the total number of the 10 production wells is 18.
The effective thickness contour diagram of the test area is shown in figure 3; the permeability contour map of the test zone is shown in fig. 4. The static characteristic is the general development difference (see fig. 3 and 4, test area is in the black frame), the average single well thickness of the test area is 6.9m, and the average single well thickness is lower than the average level of the block by 12.7%. Wherein the number proportion of oil layers below 1m is 85.4%, and the thickness proportion is 58.3%. The permeability of the test zone is 190mD, which is lower than the average level of the block by 13.6%, wherein 74.1% of the perforation point permeability is lower than 150mD.
The dynamic characteristics of the test area are that the performance injection and production capability is poor, the injection pressure is high, the injection quantity is low, the injection intensity is low, the liquid yield intensity is low, the oil layer utilization ratio below 1m is 35.9%, and is lower than 25.7% of the block. (the comparison of the dynamic indexes of the test areas and the blocks is shown in Table 6).
TABLE 6
Step 2: the single-layer plane design diagram is shown in fig. 5, and a target layer can be omitted for the well injection points with or without exploitation; for the unidirectional communication, a small layer with high proportion is used as a target layer; the well is well developed for injecting pure sandstone extraction well above 1m, and the well can be used as a target layer. And the scale design result is manually marked on the graph according to the template data, so that adjustment and modification among well groups are facilitated. The test area is designed with 17 fracturing injection wells and 8 production wells, and the fracturing well number proportion is 89.2%. 232 target layers are fractured, and the proportion of the fracturing layer number is 77.1%.
Step 3: and (3) carrying out multi-fracture fracturing by combining the intervals according to a permeability level difference method, wherein engineering factors are considered in the practical application process. The permeability level difference method layer section combination of the test area is shown in table 7, the combination result is shown in brackets, the thickness of the lower interlayer of the second small layer of the third section in the graph is influenced, the construction requirement cannot be met, only one layer can be expanded downwards, and the effective thickness is 0.2m due to the expanded small layer permeability of 119mD, so that the upper target layer cannot be influenced in the construction process. If the permeability of the expanded layer is equal to that of the target layer, a selective fracturing mode is designed, and the expanded layer is plugged according to the thickness of the expanded layer and then the target layer is constructed.
The average single well fracturing effective thickness of the test area is 3.5m, 4.6 sections are fractured, 8.5 seams are fractured, the fracturing thickness proportion is 50.7%, wherein the thickness of an oil layer below 1m is 73.9%, and the number of the oil layers is 83.5%.
TABLE 7
In the original design method, the number of the average small layers in the fracturing section is 4.2, the transformation proportion of the target layer is only 47.6%, and the difficulty of seam starting layer is large, so that the subsequent transformation and layer selection are not facilitated. By using the method, in the multi-well combined design, the number of the average small layers in the fracturing section is thinned to 2.1 in a local range, the transformation proportion of the target layer reaches 95.2%, the transformation proportion of the target layer is greatly improved, the accuracy of oil layer transformation is ensured, and the correspondence and timeliness are improved.
After the test area is implemented in one month, the average single well injection pressure drop amplitude is 2.1MPa higher than the average level, the injection strength is improved by 1.2m 3/m, the oil layer utilization ratio below 1m reaches more than 80%, and the fracturing effective period of the injection well is more than 3 months higher than the average level. The water content in the stage of the test area is reduced by 16.36 percent and is higher than 6.05 percent of the total area, the recovery ratio is improved by 8.51, and the water content is higher than 0.56 percent of the total area under the same PV.
Claims (7)
1. The chemical flooding three-dimensional fracturing process suitable for thin and thick oil layer interaction distribution is characterized by comprising the following two designs:
The whole design method comprises the following steps:
The chemical flooding development process is divided into seven stages according to injection conditions: ① Blank water injection stage; ② A pre-slug injection stage; ③ A primary slug initial stage; ④ A main slug peak period; ⑤ A main slug later stage; ⑥ A sub-slug injection stage; ⑦ Turning to a subsequent water injection stage;
the whole design method adopts the development process to design in stages, plans to reform various oil layers in steps, balances the injection and production capacity of thin and thick oil layers, and comprises three main aspects of well selection, layer selection and construction scale:
a well selection method comprises the following steps: widening the well selection range of the improved injection well, wherein part of the stages mainly improve the injection well, part of the stages synchronously reform the injection well, and part of the stages mainly improve the production well;
The concrete method for widening the well selection range of the improved injection well comprises the following steps: three types of injection wells are added at stage ①②③: ① The injection allocation is completed by more than 70 percent, and the allowable injection pressure difference is within 1 Mpa; ② The injection profile is unbalanced, and the single small layer inhalation proportion exceeds 30%; ③ The injection-recovery ratio is below 0.8, and the injection intensity is 20% lower than the average level of the whole region; fracturing the extraction well with synchronous effect while adding three injection wells in the first three stages in the ④ th stage; at the ⑤⑥ th stage, excavating residual oil potential, and fracturing a produced well with accumulated oil yield per unit thickness being more than 50% lower than the average level of the block;
b, selecting a layer method: selecting layers by layer selecting sequence and layer section combination; in the aspect of layer sequence selection, the transformation time of a thin difference layer is advanced, or the thin difference layer and a thick oil layer are synchronously transformed; in the aspect of layer segment combination, adopting a permeability level difference method to perform layer segment combination;
C in terms of construction scale: calculating a target layer comprehensive index by using common parameters, and designing a construction scale by using the target layer comprehensive index to ensure that all the modified oil layer developments reach the highest extraction degree under the optimal penetration ratio;
the design method of the local multi-well group comprises the following steps:
The local multi-well group design method is based on a staged design strategy, and is characterized in that when a plurality of well groups with approximate dynamic and static characteristics appear in a block connection, on the basis of the original single injection well design, a single well design is expanded into a multi-well synchronous design by combining dynamic development indexes and dynamic monitoring indexes, geological design synchronous construction design is carried out, a fracturing target layer is combined, and the connection well group is used as a whole for fracturing transformation;
The local multi-well group design method specifically comprises the following steps:
Step 1: determining a transformation range and the number of wells according to dynamic development indexes, wherein the requirements relate to not less than 4 adjacent well groups, and changing the original single well group analysis into multi-well group analysis; referring to dynamic development indexes, the indexes of more than 80% in the well selection range are lower than 80% of the average level of the whole area, and the number of the transformed wells in the range reaches more than 70%;
Step 2: according to the dynamic monitoring index, well monitoring and other dynamic and static data which are easily acquired by an oil field are utilized to carry out multi-well synchronous geology and scale design on the same deposition plan; the method aims at guiding scale design by using development geological data, and meeting the development geological requirements through the scale design;
Step 3: and combining the fracturing target layers, and further reducing the level difference range by a permeability level difference refining method to reduce the number of small layers in the fracturing layer section to 2-3 layers.
2. The chemical flooding three-dimensional fracturing process suitable for alternating distribution of thin and thick oil layers according to claim 1, wherein the process is characterized by: the concrete method for widening the well selection range of the improved injection well comprises the following steps: the extraction end is matched with the injection end to carry out synchronous reconstruction on the same horizon; the method for excavating potential of residual oil comprises the step of synchronously reforming an injection well by matching with the same horizon of a production end.
3. The chemical flooding three-dimensional fracturing process suitable for alternating distribution of thin and thick oil layers according to claim 1, wherein the process is characterized by:
The specific method for improving the thin difference layer or synchronously improving the thick oil layer is as follows: the thin differential layer is preferably modified first in stage ①②③; synchronously reforming a thin oil layer and a thick oil layer in the ④ th stage; the ⑤⑥ th stage is not modified by a thick oil layer;
in the case of interval combination, the interval combination is performed using a permeability level difference method.
4. The chemical flooding three-dimensional fracturing process suitable for alternating distribution of thin and thick oil layers according to claim 3, wherein the process comprises the following steps of: the method for carrying out interval combination by the permeability level difference method comprises the following steps: the interlayer contradiction is relieved by segmentation, so that cracks are relatively uniformly distributed in an oil layer; increasing the number of fracturing sections of the whole well and the number of layers of the reconstruction purpose; the permeability level difference in the fracturing section is within 20% of the permeability level difference of the present well; when the permeability level difference method is used, the level difference range is narrowed with the increase of the highest permeability of the target layer: when the highest permeability is below 70 millidarcy, the in-segment level difference has smaller influence; when the highest permeability is 70-200 millidarcy, the range of the level difference in the fracturing section is kept to be 1-2; when the highest permeability is higher than 200 millidarcies, the intra-fracture zone differential size ranges from 1 to 1.2.
5. The chemical flooding three-dimensional fracturing process suitable for alternating distribution of thin and thick oil layers according to claim 1, wherein the process is characterized by: the method for calculating the comprehensive index of the target layer comprises the following steps: calculating average sandstone thickness, average effective thickness, average permeability and communication direction number according to the layers by taking the target layer as a center; classifying the calculation results, multiplying the calculation results by corresponding coefficients respectively according to the classification results, and summing to obtain a target layer comprehensive index; according to the method for selecting the construction scale of the target layer, the construction scale is selected according to the comprehensive index of the target layer, different construction scales can generate different crack radiuses, and the different crack radiuses correspond to different crack penetration ratios and extraction degrees, that is, the best construction scale corresponds to the highest extraction degree; when the different requirements of multiple well groups in multiple directions are balanced on a plane, the total penetration ratio of the optimal directions of all well point planes is required to be not higher than 35%, so that the problem of water content of blocks caused by sudden flooding is effectively avoided when the two stages are developed.
6. The chemical flooding three-dimensional fracturing process suitable for alternating distribution of thin and thick oil layers according to claim 1, wherein the process is characterized by: the step 2 is to radiate from the central well of the first well group at the side to the communicating well, then radiate to a plurality of communicating wells according to the well row of the central well, and then determine well point targets one by one and simultaneously perform scale design.
7. The chemical flooding three-dimensional fracturing process suitable for alternating distribution of thin and thick oil layers according to claim 6, wherein the chemical flooding three-dimensional fracturing process is characterized in that: the principle of determining the well point target is a differential principle, the monitored data shows that the differential proportion is lower than 25% of the whole well, and the standard range is determined to be 20-30% according to the actual condition of the block.
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