CN105156086A - Method for forming volume fracturing network - Google Patents

Abstract

The invention provides a method for forming a volume fracturing network, and belongs to the technical field of shale gas reservoir transformation. The method comprises the following steps: acquiring a maximum value of a difference between a horizontal stress along a first preset direction and a horizontal stress along a second preset direction at a preset shale reservoir; when the maximum difference value corresponds to a first extreme value position and a second extreme value position in a preset shale reservoir, respectively fracturing in a direction extending outwards perpendicular to a connecting line between the first extreme value position and the second extreme value position to form a first fracture and a second fracture; and fracturing in a direction perpendicular to the connecting line of the first extreme position and the second extreme position to form a third crack. The invention provides the fracturing method of the third-order stress resonance and the fourth-order stress resonance according to the maximum value of the difference between the horizontal stresses along the first preset direction and the second preset direction, so that the method is suitable for high-stress-difference stratums, can be used for site fracturing construction, and has better economic benefit and application prospect.

Description

A kind of formation method of volume fracturing seam net

Technical field

The present invention relates to the formation method of a kind of volume fracturing seam net, belong to shale gas reservoir stimulation technology field.

Background technology

The key core of volume fracturing technology is mechanics problem, for initial in-site stress field, particularly controls in the forming process of seam net in initial level main stress bar difference, when two is less to horizontal principal stress difference, easily forms seam net, otherwise then not easily forms seam net.Initial in-site stress field objective reality is in stratum, and the numerical value of mean level minimum principal stress and horizontal major principal stress is different, namely there is horizontal principal stress difference.

At present, there are some researches show that the generation of artificial hydraulic fracture reduces the horizontal deviator stress value in stratum.Based on this principle, for low stress difference shale gas reservoir, prior art proposes a kind of TexasTwo-Step fracturing process, namely replaces fracturing process.Shown in composition graphs 1, the pressure break order that should replace fracturing process is: 2-> crack, 1-> crack, crack 3.But alternately should can only form seam net when two is less to horizontal principal stress difference by fracturing process, and be only applicable to low stress difference shale reservoir, the area extensively distributed for heavily stressed poor shale reservoir then cannot be suitable for.

Summary of the invention

The present invention is the problem that cannot be applicable to heavily stressed poor shale reservoir solving the existence of existing volume fracturing technology, and then proposes the formation method of a kind of volume fracturing seam net, specifically comprises following technical scheme:

A formation method for volume fracturing seam net, comprising:

The difference maximum value between the horizontal stress along the first predetermined direction and the horizontal stress along the second predetermined direction is obtained at predetermined shale reservoir;

When described difference maximum value at described predetermined shale reservoir to when should have the first extreme value place and a secondary extremal position, on the direction that the line vertically between described first extreme value place and described secondary extremal position extends laterally, each pressure break forms the first crack and the second crack;

The 3rd crack is formed along pressure break on the line direction of vertical described first extreme value place and described secondary extremal position in the plane of the horizontal stress of described first predetermined direction with the horizontal stress place of the second predetermined direction.

A formation method for volume fracturing seam net, comprising:

The difference maximum value between the horizontal stress along the first predetermined direction and the horizontal stress along the second predetermined direction is obtained at predetermined shale reservoir;

When described difference maximum value at described predetermined shale reservoir to when should have the 3rd extreme value place, form the 4th crack and the 5th crack in the both sides of described 3rd extreme value place along pressure break each on the direction of vertical-horizontal stress.

The invention has the beneficial effects as follows: according to along the difference maximum value between the first predetermined direction and the horizontal stress of the second predetermined direction, propose the fracturing process of third power stress " resonance " and four secondary stress " resonance ", thus heavily stressed poor stratum can be applicable to, the method can be used for on-the-spot pressing crack construction, has good economic benefit and application prospect.

Accompanying drawing explanation

Fig. 1 is TexasTwo-Step fracturing process schematic diagram of the prior art, and label a wherein represents crack 1, and label b represents crack 2, and label c represents crack 3, and label A represents complicated seam web frame.

Fig. 2 is the change of stress field schematic diagram that the generation of hydraulic fracture causes.

Fig. 3 is crack-induced stress and difference variation tendency schematic diagram thereof, and abscissa wherein represents zero dimension distance, and ordinate represents STRESS VARIATION amount and/or net impact, and curve d represents Δ σ _yvalue, curve e represents Δ σ _xvalue, curve f represents Δ σ _x-Δ σ _yvalue.

Fig. 4 shows the flow chart of the formation method of the first volume fracturing seam net in an illustrative manner.

Fig. 5 shows the flow chart of the formation method of the second volume fracturing seam net in an illustrative manner.

Fig. 6 is the flow chart of the formation method of the volume fracturing seam net that embodiment one provides.

Fig. 7 is third power stress " resonance " the pressure break mode schematic diagram that embodiment one provides.

Fig. 8 is third power stress " resonance " the pressure break mode sequence of construction that embodiment one provides and the seam web area schematic diagram finally formed.

Fig. 9 is the flow chart of the formation method of the volume fracturing seam net that embodiment two provides.

Figure 10 is four secondary stress " resonance " the pressure break mode schematic diagram that embodiment two provides.

Figure 11 is four secondary stress " resonance " the pressure break mode sequence of construction that embodiment two provides and the seam web area schematic diagram finally formed.

Detailed description of the invention

In the state of the art, near hydraulic fracture, the crack-induced stress of stratum any point obtains by following formulae discovery:

$\frac{1}{2}({\mathrm{\Δ\σ}}_X+{\mathrm{\Δ\σ}}_Y)=-p_0\{\frac{r}{\sqrt{r_1{r}_2}}cos(\mathrm{\θ}-0.5{\mathrm{\θ}}_1-0.5{\mathrm{\θ}}_2)-1\}$

$\frac{1}{2}({\mathrm{\Δ\σ}}_X-{\mathrm{\Δ\σ}}_Y)=p_0\frac{2rsin\mathrm{\θ}}{L}{\left(\frac{L^2}{4r_1{r}_2}\right)}^{3/2}sin\left(\frac{3}{2}\right({\mathrm{\θ}}_1+{\mathrm{\θ}}_2))$

Wherein, p ₀represent fracture propagation net pressure; Δ σ _xwith Δ σ _yrepresent the crack-induced stress of X-direction and Y-direction respectively, r represents the distance of stratum any point and fracture surface central point, r ₁and r ₂represent the distance of stratum any point and fracture surface two end points respectively, θ represents the line of stratum any point to fracture surface central point and the angle of fracture surface, θ ₁and θ ₂represent the line of stratum any point to fracture surface two end points and the angle of fracture surface respectively, L represents fracture length.

Shown in composition graphs 2 is the change of stress field schematic diagram that the generation of hydraulic fracture causes, σ wherein _hminand σ _hmaxrepresent stratum initial level minimum principal stress and horizontal major principal stress respectively.

Shown in composition graphs 3, distance fracture surface on the x-axis times fracture half-length position two is maximum to the difference of horizontal fracture induced stress, i.e. Δ σ _x-Δ σ _ymaximum value is reached at this point.When adopting existing TexasTwo-Step fracturing process, Δ σ _x-Δ σ _ymaximum value occur in distance fracture surface times fracture half-length place, its value is the crack net pressure of 0.7698 times, but increases with length apart from fracture surface, and comparatively fast, therefore existing TexasTwo-Step fracturing process is only applicable to the poor stratum of low stress, is not suitable for heavily stressed poor stratum in decay.

But can know from Fig. 3, Δ σ _x-Δ σ _ymaximum value occur in , namely there is stress upset at first herein in place.Based on this conclusion and principle, for initial high stress difference shale formation, the Δ σ of many hydraulic fractures can be allowed _x-Δ σ _ymaximum value occurs in same point, produces stress " resonance " phenomenon, then can overcome the larger stress difference of primary stress field herein, produces stress upset, thus produces seam web frame.Therefore embodiments of the invention are for existing higher stress difference shale reservoir, propose the fracturing process of third power stress " resonance " and four secondary stress " resonance ", enable to produce complicated seam net, promote unconventional reservoir oil-gas mining effect.

Embodiments of the invention propose the formation method of a kind of volume fracturing seam net, and shown in composition graphs 4, the method comprises:

Step 41, obtains the difference maximum value between the horizontal stress along the first predetermined direction and the horizontal stress along the second predetermined direction at predetermined shale reservoir.

Wherein, the first predetermined direction can be and the direction of plane-parallel (i.e. X-axis), and the second predetermined direction can be and the direction of horizontal plane (i.e. Y-axis).This difference maximum value can be the difference between the horizontal maximum stress value of Y-axis and the horizontal minimum stress value of X-axis.

Step 42, when difference maximum value at predetermined shale reservoir to when should have the first extreme value place and a secondary extremal position, on the direction that the line between vertical first extreme value place and secondary extremal position extends laterally, each pressure break forms the first crack and the second crack.

When existence two extreme value places, the present embodiment can adopt the pressure break mode of third power stress " resonance " to weaken the anisotropy of formation stress field, thus produces the seam web frame of third power stress " resonance ".For any one extreme value place, there is the Δ σ of three cracks _x-Δ σ _ymaximum value occurs in this position, and in this position, stress " resonance " phenomenon occurs, and therefore the stress anisotropy of the primary stress field of this position has been weakened severely, and stress upset even occurs, thus produces seam web frame.

Optionally, in concrete work progress, first in the position having the first preset distance with the first extreme value place and have the first preset distance with secondary extremal position, pressure break forms the first crack respectively, then in the position having the second preset distance with the first extreme value place and have the second preset distance with secondary extremal position, pressure break forms the second crack respectively, and the first preset distance is wherein greater than the second preset distance.

Step 43, forms the 3rd crack along pressure break on the line direction of vertical first extreme value place and secondary extremal position in the plane of the horizontal stress of the first predetermined direction with the horizontal stress place of the second predetermined direction.

Behind formation two the first cracks and two the second cracks, on the line direction of vertical first extreme value place and secondary extremal position, pressure break can form the 3rd crack.

Wherein, the first crack, following relational expression can be met between the second crack and the 3rd crack:

$\left\{\begin{array}{c}\frac{1}{\sqrt{2}}(\frac{L_1}{2}-\frac{L_2}{2})=D_1\\ \frac{1}{\sqrt{2}}(\frac{L_2}{2}+\frac{L}{2})=D_2\\ L_2>L_3\end{array}\right.$

Wherein, L ₁represent the length in the first crack, L ₂represent the length in the second crack, L ₃represent trilete length, D ₁represent the distance between the first crack and the second crack, D ₂represent the distance between the second crack and the 3rd crack.

Embodiments of the invention also proposed the formation method of a kind of volume fracturing seam net, and shown in composition graphs 5, the method comprises:

Step 51, obtains the difference maximum value between the horizontal stress along the first predetermined direction and the horizontal stress along the second predetermined direction at predetermined shale reservoir.

Wherein, the first predetermined direction can be and the direction of plane-parallel (i.e. X-axis), and the second predetermined direction can be and the direction of horizontal plane (i.e. Y-axis).This difference maximum value can be the difference between the horizontal maximum stress value of Y-axis and the horizontal minimum stress value of X-axis.

Step 52, when difference maximum value at predetermined shale reservoir to when should have the 3rd extreme value place, form the 4th crack and the 5th crack in the both sides of the 3rd extreme value place along pressure break each on the direction of vertical-horizontal stress.

When only there is an extreme value place, the present embodiment can adopt the pressure break mode of four secondary stress " resonance " to weaken the anisotropy of formation stress field, thus produces the seam web frame of four secondary stress " resonance ".Owing to having four cracks same extreme value place generation stress " resonance ", then the most easily there is stress upset in this extreme value place, thus produce seam web frame.

Optionally, in concrete work progress, first in the position having the 3rd preset distance with the 3rd extreme value place, pressure break forms the 4th crack respectively, then in the position having the 4th preset distance with the 3rd extreme value place, respectively pressure break forms the 5th crack, and the 3rd preset distance is greater than the 4th preset distance.

Wherein, following relational expression can be met between the 4th crack and the 5th crack:

$\left\{\begin{array}{c}\frac{1}{\sqrt{2}}(\frac{L_4}{2}-\frac{L_5}{2})=D_3\\ \frac{1}{\sqrt{2}}\frac{L_5}{2}=\frac{D_4}{2}\end{array}\right.$

Wherein, L ₄represent the length in the 4th crack, L ₅represent the length in the 5th crack, D ₃represent the distance between the 4th crack and the 5th crack, D ₄represent the distance between two the 5th cracks.

Be described in detail below by the formation method of specific embodiment to described volume fracturing seam net:

Embodiment one

Shown in composition graphs 6, the formation method of the volume fracturing seam net that the present embodiment provides comprises:

Step 61, obtains the difference maximum value between the horizontal stress along X-direction and the horizontal stress along Y direction at predetermined shale reservoir.

Wherein, if X-direction is horizontal minimum principal stress direction, size is 25MPa, and Y direction is horizontal biggest principal stress direction, and size is 37MPa, then level two is S22-S11=37-25=12MPa to main stress bar difference.

Step 62, when difference maximum value at predetermined shale reservoir to when should have B position and a C position, in the plane of the horizontal stress of X-direction with the horizontal stress place of Y direction, form the first crack along pressure break on the direction that the line between vertical B position and C position extends laterally.

When there is B and C two extreme value places as shown in Figure 7, the present embodiment can adopt the pressure break mode of third power stress " resonance " to weaken the anisotropy of formation stress field, thus produces the seam web frame shown in composition graphs 8.In Fig. 7 one extreme value place (such as B position) is had to the Δ σ of three cracks _x-Δ σ _ymaximum value occurs in this position, and in this position, stress " resonance " phenomenon occurs, and therefore the stress anisotropy of the primary stress field of this position has been weakened severely, and stress upset even occurs, thus produces seam web frame.

Employing third power stress " resonance " pressure break mode sequence of construction shown in Fig. 8 and the final seam web area formed, for the situation (the B position namely in Fig. 7 and C position) of existence two extreme value places, the direction that extends laterally of the line first between B position and C position can form the first crack at each pressure break.Wherein, the first crack and the distance between B position and C position equal the first fracture length respectively doubly.

Step 63, forms the second crack along pressure break on the direction that the line of vertical B position and C position extends laterally in the plane of the horizontal stress of X-direction with the horizontal stress place of Y direction.

After pressure break forms the first crack, the direction that extends laterally of the line between B position in the figure 7 and C position can form the second crack at each pressure break.Wherein, the second crack and the distance between B position and C position equal the second fracture length respectively doubly.

Optionally, formed in the process in the first crack and the second crack in pressure break, the first crack and the second crack can be generated by the order 1., 2., 3., 4. and 5. of label shown in Fig. 8 successively pressure break, what even first formed is nearer the first crack, distance B position, and then form the first nearer crack of distance C position, then formed in pressure break in the process in the second crack and first form the second nearer crack of distance C position, and then forming the second nearer crack of distance B position, the crack generated successively by this order has good stability.

Step 64, forms the 3rd crack along pressure break on the line direction of vertical B position and C position in the plane of the horizontal stress of X-direction with the horizontal stress place of Y direction.

Behind formation two the first cracks and two the second cracks, in the plane of the horizontal stress of X-direction with the horizontal stress place of Y direction, can form the 3rd crack along pressure break on the line direction of vertical B position and C position, the distance of the 3rd distance B position, crack and C position is equal to the 3rd fracture length doubly.

Optionally, the first crack, following relational expression can be met between the second crack and the 3rd crack:

$\left\{\begin{array}{c}\frac{1}{\sqrt{2}}(\frac{L_1}{2}-\frac{L_2}{2})=150\\ \frac{1}{\sqrt{2}}(\frac{L_2}{2}+\frac{L_3}{2})=150\\ L_2>L_3\end{array}\right.$

Wherein, L ₁represent the length in the first crack, L ₂represent the length in the second crack, L ₃represent trilete length.When determining that the first crack and the second crack and the distance between the second crack and the 3rd crack are 150 meters by measurement, then determine L by above-mentioned formula ₁, L ₂and L ₃between meet relation.

Embodiment two

Shown in composition graphs 9, the formation method of the volume fracturing seam net that the present embodiment provides comprises:

Step 91, obtains the difference maximum value between the horizontal stress along X-direction and the horizontal stress along Y direction at predetermined shale reservoir.

Wherein, if X-direction is horizontal minimum principal stress direction, size is 25MPa, and Y direction is horizontal biggest principal stress direction, and size is 37MPa, then level two is S22-S11=37-25=12MPa to main stress bar difference.

Step 92, when difference maximum value at predetermined shale reservoir to when should have a D position, form the 4th crack in the both sides of D position along pressure break on the direction of vertical-horizontal stress.

When only there is an extreme value place, such as, D position shown in Figure 10, the present embodiment can adopt the pressure break mode of four secondary stress " resonance " to weaken the anisotropy of formation stress field, thus produces in conjunction with the seam web frame shown in Figure 11.Extreme value place (i.e. D position) in Figure 10 is had to the Δ σ of four cracks _x-Δ σ _ymaximum value occurs in this position, and in this position, stress " resonance " phenomenon occurs, and therefore the stress anisotropy of the primary stress field of this position has been weakened severely, and therefore stress upset more easily occurs, thus produces seam web frame.

Employing four secondary stress " resonance " pressure break mode sequence of construction shown in Figure 11 and the final seam web area formed, for the situation (the D position namely in Figure 10) of the extreme value place of existence anduniquess, first the 4th crack can be formed in both sides, D position along perpendicular to each pressure break on the direction of horizontal stress.Wherein, the distance between the 4th crack and D position equals the 4th fracture length doubly.

Step 93, forms the 5th crack in the both sides of D position along pressure break on the direction of vertical-horizontal stress.

Pressure break is formed behind the 4th crack, can form the 5th crack along the both sides, D position in Figure 10 perpendicular to pressure break each on the direction of horizontal stress.Wherein, the distance between the 5th crack and D position equals the 5th fracture length doubly.

Optionally, in the process that pressure break forms the 4th crack and the 5th crack, can by label shown in Figure 10 1., 2., 3. order and 4. successively pressure break generates the 4th crack and the 5th crack, the 4th crack that the position pressure break even in the left side with D position with the 3rd preset distance is formed is early than the 4th crack formed in the position pressure break having the 3rd preset distance with side, D position second, the 5th crack that the 5th crack that the position pressure break then having the 4th preset distance in the second side with D position is formed is formed early than the position pressure break having the 4th preset distance in the first side with D position, the crack generated successively by this order has good stability.

Wherein, following relational expression can be met between the 4th crack and the 5th crack:

$\left\{\begin{array}{c}\frac{1}{\sqrt{2}}(\frac{L_4}{2}-\frac{L_5}{2})=100\\ \frac{L_5}{\sqrt{2}}=200\end{array}\right.$

Wherein, L ₄represent the length in the 4th crack, L ₅represent the length in the 5th crack.When being determined that by measurement the distance between the 4th crack and the 5th crack is 100 meters, then determine L by above-mentioned formula ₄and L ₅between meet relation.

The formation method of volume fracturing that this detailed description of the invention provides seam net is according to along the difference maximum value between the first predetermined direction and the horizontal stress of the second predetermined direction, propose the fracturing process of third power stress " resonance " and four secondary stress " resonance ", thus can be applicable to adopt TexasTwo-Step fracturing process cannot obtain the heavily stressed poor stratum of complicated seam web frame, and then improve fracturing effect and increase Oil/gas Well output, the method can be used for on-the-spot pressing crack construction, has good economic benefit and application prospect.

This detailed description of the invention is clearly and completely described technical scheme of the present invention, and embodiment is wherein only a part of embodiment of the present invention, and is not whole embodiments.Based on the embodiment in the present invention, other embodiments all that those skilled in the art are not obtaining under the prerequisite of creative work all belong to protection scope of the present invention.

Claims (10)

1. a formation method for volume fracturing seam net, is characterized in that, comprising:

The difference maximum value between the horizontal stress along the first predetermined direction and the horizontal stress along the second predetermined direction is obtained at predetermined shale reservoir;

When described difference maximum value at described predetermined shale reservoir to when should have the first extreme value place and a secondary extremal location point, on the direction that the line vertically between described first extreme value place and described secondary extremal position extends laterally, each pressure break forms the first crack and the second crack;

The 3rd crack is formed along pressure break on the line direction of vertical described first extreme value place and described secondary extremal position in the plane of the horizontal stress of described first predetermined direction with the horizontal stress place of the second predetermined direction.

2. the method for claim 1, is characterized in that, described difference maximum value is the difference between the horizontal maximum stress value of described first predetermined direction and the horizontal minimum stress value of described second predetermined direction.

3. method as claimed in claim 1 or 2, is characterized in that, described first crack, meets following relational expression between the second crack and the 3rd crack:

$\left\{\begin{array}{c}\frac{1}{\sqrt{2}}(\frac{L_1}{2}-\frac{L_2}{2})=D_1\\ \frac{1}{\sqrt{2}}(\frac{L_2}{2}+\frac{L_3}{2})=D_2\\ L_2>L_3\end{array}\right.$

Wherein, L ₁represent the length in the first crack, L ₂represent the length in the second crack, L ₃represent trilete length, D ₁represent the distance between the first crack and the second crack, D ₂represent the distance between the second crack and the 3rd crack.

4. method as claimed in claim 3, is characterized in that, on the direction that the line vertically between described first extreme value place and described secondary extremal position extends laterally, each pressure break forms the first crack and the second crack and comprises:

With described first extreme value place distance the first preset distance and with the position of described secondary extremal positional distance first preset distance respectively pressure break form the first crack;

With described first extreme value place distance the second preset distance and with the position of described secondary extremal positional distance second preset distance respectively pressure break form the second crack, described first preset distance is greater than described second preset distance.

5. method as claimed in claim 4, it is characterized in that, if in the first crack that the position pressure break having the first preset distance with described first extreme value place is formed early than the first crack formed in the position pressure break that there is the first preset distance with described secondary extremal position, then in the second crack that the position pressure break having the second preset distance with described secondary extremal position is formed early than the second crack formed in the position pressure break that there is the second preset distance with described first extreme value place.

6. a formation method for volume fracturing seam net, is characterized in that, comprising:

The difference maximum value between the horizontal stress along the first predetermined direction and the horizontal stress along the second predetermined direction is obtained at predetermined shale reservoir;

When described difference maximum value at described predetermined shale reservoir to when should have the 3rd extreme value place, form the 4th crack and the 5th crack in the both sides of described 3rd extreme value place along pressure break each on the direction of vertical-horizontal stress.

7. method as claimed in claim 6, it is characterized in that, described difference maximum value is the difference between the horizontal maximum stress value of described first predetermined direction and the horizontal minimum stress value of described second predetermined direction.

8. method as claimed in claims 6 or 7, it is characterized in that, described 4th crack and the 5th crack meet following relational expression:

$\left\{\begin{array}{c}\frac{1}{\sqrt{2}}(\frac{L_4}{2}-\frac{L_5}{2})=D_3\\ \frac{1}{\sqrt{2}}\frac{L_5}{2}=\frac{D_4}{2}\end{array}\right.$

Wherein, L ₄represent the length in the 4th crack, L ₅represent the length in the 5th crack, D ₃represent the distance between the 4th crack and the 5th crack, D ₄represent the distance between two the 5th cracks.

9. method as claimed in claim 8, it is characterized in that, in the plane of the horizontal stress of described first predetermined direction with the horizontal stress place of the second predetermined direction, form the 4th crack and the 5th crack along the both sides of vertical described 3rd extreme value place along each pressure break on the direction of described horizontal stress comprise:

In the position having the 3rd preset distance with described 3rd extreme value place, respectively pressure break forms the 4th crack;

In the position having the 4th preset distance with described 3rd extreme value place, respectively pressure break forms the 5th crack, and described 3rd preset distance is greater than described 4th preset distance.

10. method as claimed in claim 9, it is characterized in that, if the 4th crack that the position pressure break having the 3rd preset distance in the first side with described 3rd extreme value place is formed is early than the 4th crack formed in the position pressure break having the 3rd preset distance with described 3rd extreme value place second side, then the 5th crack that the 5th crack that the position pressure break having the 4th preset distance in the second side with described 3rd extreme value place is formed is formed early than the position pressure break having the 4th preset distance in the first side with described 3rd extreme value place.