Method for comprehensive evaluation of shale fracability under the geology-engineering “double-track” system

Abstract

The present invention discloses a method for comprehensive evaluation of shale fracability under the geology-engineering “double-track” system, comprising the following steps: S1: Divide the target horizontal fracturing interval into multiple sampling sections; S2: Establish the reservoir property evaluation factor of each sampling section, and calculate the geological evaluation index of the target horizontal fracturing interval according to the reservoir property evaluation factor of each sampling section; S3: Establish the brittleness factor, natural fracture factor and natural fracture opening factor of each sampling section, and then establish the engineering evaluation index of each sampling section according to these factors; S4: Calculate the engineering evaluation index of the target horizontal fracturing interval according to the engineering evaluation factor of each sampling section; S5: Evaluate the fracability of the target horizontal fracturing interval according to the geological evaluation index and the engineering evaluation index.

Claims

1. A method for evaluation of shale fracability under geology-engineering “double-track” system, comprising the following steps: S1: Divide a target horizontal fracturing interval into multiple sampling sections; S2: Establish a reservoir property evaluation factor of each sampling section, and calculate a geological evaluation index of the target horizontal fracturing interval according to the reservoir property evaluation factor of each sampling section; S3: Establish a brittleness factor, a natural fracture factor and a natural fracture opening factor of each sampling section, and then establish an engineering evaluation index of each sampling section according to the brittleness factor, the natural fracture factor and the natural fracture opening factor of each sampling section; The brittleness factor is calculated according to the following equations: $C_i=\lambda \left[1-\exp \left(\begin{array}{c}{M}_i\\ E_i\end{array}\right)\right]+\begin{array}{c}\eta \left({\sigma }_{\mathrm{pi}}-{\sigma }_{\mathrm{ci}}\right)\\ {\sigma }_{\mathrm{pi}}\end{array}$ $\lambda +\eta =1$ Where, C.sub.i is the brittleness factor of the sampling section i based on a stress-strain curve, dimensionless; λ and η are standardized coefficients, dimensionless; M.sub.i is a softening modulus of the sampling section i, in gigapascals (Gpa); E.sub.i is an elasticity modulus of the sampling section i, in GPa; σ.sub.pi is a peak strength obtained from a triaxial compression test at the sampling section i, in megapascals (Mpa); σ.sub.ci is a participating strength obtained from the triaxial compression test at the sampling section i, in MPa; The natural fracture factor is calculated according to the following equations: $\underset{\mathrm{Fi}}{P}=\frac{P_{\mathrm{fi}}-P_{f\min }}{P_{f\max }-P_{f\min }}$ $P_{\mathrm{fi}}=\frac{2E^2}{\left(\underset{1i}{K^2}+\underset{2i}{K^2}\right)\underset{i}{\upsilon }}$ $\underset{1i}{K}=\underset{i}{0.3172\rho }+\frac{0.0457}{V_{ci}}+\underset{i}{0.2131\ln \left(\mathrm{DT}\right)\times 0.5041}$ $\underset{2i}{K}=\underset{i}{2.1332\rho }+\frac{0.0768}{V_{ci}}+\underset{i}{1.1886\ln \left(\mathrm{DT}\right)\times 9.1808}$ Where, P.sub.Fi is the natural fracture factor of the sampling section i, dimensionless; P.sub.fi is a representation number of natural fracture development degree in sampling section i, ×10.sup.6 m.sup.−1; P.sub.fmax and P.sub.fmin are respectively maximum and minimum representation numbers of natural fracture development degree in all sampling sections, ×10.sup.6 m.sup.−1; K.sub.1i and K.sub.2i are respectively Type I and Type II fracture toughness of the sampling section i, in MPa.Math.m.sup.0.5; ν.sub.i is an average static Poisson's ratio of the sampling section i, dimensionless; ρ.sub.i is an average shale density of the sampling section i, in g/cm.sup.3; V.sub.ci is an average mud content of the sampling section i, in percentage (%); DT.sub.i is an average acoustic time difference of the sampling section i, in μs/m; The natural fracture opening factor is calculated according to the following equations: $\begin{array}{cc}\underset{\mathrm{Ti}}{P}=\frac{P_{t\max }-P_{\mathrm{ti}}}{P_{t\max }-P_{t\min }}& \left(12\right)\end{array}$ $\underset{\mathrm{ti}}{P}=\underset{\mathrm{xi}}{\sigma }{\underset{1i}{l}}^2+\underset{\mathrm{yi}}{\sigma }{\underset{2i}{l}}^2+\underset{\mathrm{zi}}{\sigma }{\underset{3i}{l}}^2+2\tau \underset{\mathrm{xyi}1i2i}{\mathrm{ll}}+2\tau \underset{\mathrm{yzi}2i3i}{\mathrm{ll}}+2\tau \underset{\mathrm{zxi}1i3i}{\mathrm{ll}}$ $l_{1i}=\sqrt{\frac{1-l_{3i}^2}{1+{\tan }^2{\theta }_i}}$ $l_{2i}=l_{1i}\tan {\theta }_i$ $l_{3i}=\cos {\alpha }_i$ Where, P.sub.Ti is the natural fracture opening factor of the sampling section i, dimensionless; P.sub.ti is a fluid pressure when a natural fracture of the sampling section i is opened, in MPa; P.sub.tmax and P.sub.tmin are respectively maximum and minimum fluid pressures in all sampling sections to meet the opening of the natural fracture, in MPa; σ.sub.xi, σ.sub.yi and σ.sub.zi are respectively normal stress, tangential normal stress and vertical stress of a shaft in the sampling section i, in MPa; l.sub.1i, l.sub.2i and l.sub.3i are respectively cosine values of an included angle between the natural fracture and maximum horizontal principal stress, minimum horizontal principal stress and vertical stress in the sampling section i, dimensionless; τ.sub.xyi, τ.sub.yzi and τ.sub.xzi are respectively shear stress components of the sampling section i, in MPa; θ.sub.i is the included angle between the natural fracture and the maximum horizontal principal stress, the minimum horizontal principal stress and the vertical stress in the sampling section i, in degrees (°); α.sub.1 is a dip angle of the natural fracture in the sampling section i, in degrees (°); S4: Calculate an engineering evaluation index of the target horizontal fracturing interval according to the engineering evaluation index of each sampling section; S5: Evaluate the shale fracability of the target horizontal fracturing interval according to the geological evaluation index and the engineering evaluation index; S6: Establish a fracturing construction scheme for the target horizontal fracturing interval according to the geological evaluation index and the engineering evaluation index; wherein, in step S6, the fracturing construction scheme for the target horizontal fracturing interval is established according to the geological evaluation index and the engineering evaluation index, specifically as follows: when the geological evaluation index is within a range of [0,0.1] and the engineering evaluation index is within a range of [0,1.0], fracturing construction of the target horizontal fracturing interval will be abandoned when the geological evaluation index is within a range of [0.1,0.4] and the engineering evaluation index is within a range of [0,0.7], and when the geological evaluation index is within a range of [0.4,0.7] and the engineering evaluation index is within a range of [0.7,1.0], slickwater fracturing+fiber temporary plugging and diverting will be carried out for the target horizontal fracturing interval when the geological evaluation index is within the range of [0.1,0.4], and the engineering evaluation index is within the range of [0.7,1.0], slickwater fracturing will be carried out for the target horizontal fracturing interval; when the geological evaluation index is within the range of [0.4,0.7] and the engineering evaluation index is within a range of [0,0.3], and when the geological evaluation index is within a range of [0.7,1.0] and the engineering evaluation index is within a range of [0.3,0.7], large-scale fracturing+fiber temporary plugging and diverting+medium multi-clustered volume fracturing will be carried out for the target horizontal fracturing interval, the large-scale fracturing means that liquid intensity for fracturing is 150% of that for the slickwater fracturing when the geological evaluation index is within the range of [0.4,0.7] and the engineering evaluation index is within the range of [0.3,0.7], and when the geological evaluation index is within the range of [0.7,1.0] and the engineering evaluation index is within the range of [0.7,1.0], large-scale fracturing+fiber temporary plugging and diverting will be carried out for the target horizontal fracturing interval; when the geological evaluation index is within the range of [0.7,1.0] and the engineering evaluation index is within the range of [0,0.3], large-scale fracturing+fiber temporary plugging and diverting+multi-clustered volume fracturing will be carried out for the target horizontal fracturing interval.

2. The method for evaluation of the shale fracability under the geology-engineering “double-track” system according to claim 1, wherein, in step S2, the reservoir property evaluation factor is calculated according to the following equations: $e_i=a_1{\phi }_i^{\prime }+b_1{\omega }_i^{\prime }$ $a_1+b_1=1$ ${\phi }_i^{\prime }=\frac{\left({\phi }_{\mathrm{ie}}-{\phi }_{\min }\right)}{\left({\phi }_{\max }-{\phi }_{\min }\right)}$ ${\omega }_i^{\prime }=\frac{\left({\omega }_i-{\omega }_{\min }\right)}{\left({\omega }_{\max }-{\omega }_{\min }\right)}$ Where, e.sub.i is the reservoir property evaluation factor of the sampling section i, dimensionless; a.sub.1 and b.sub.1 are weight coefficients of physical properties, dimensionless; ϕ.sub.i′ is a porosity of the sampling section i, dimensionless; ω.sub.i′ is a total organic carbon content of the sampling section i, dimensionless; ϕ.sub.ie is an effective porosity of the sampling section i, in %; ϕ.sub.max and ϕ.sub.min are respectively maximum effective porosity and minimum effective porosity in all sampling sections, in %; ω.sub.i is a total organic carbon content of the sampling section i, in %; ω.sub.max and ω.sub.min are respectively maximum total organic carbon content and minimum total organic carbon content in all sampling sections, in %.

3. The method for the evaluation of the shale fracability under the geology-engineering “double-track” system according to claim 2, wherein when the effective porosity of the sampling section is greater than or equal to 4.5%, a.sub.1 and b.sub.1 are 0.65 and 0.35 respectively; and when the effective porosity of the sampling section is less than 4.5%, a.sub.1 and b.sub.1 are 0.55 and 0.45 respectively.

4. The method for the evaluation of the shale fracability under the geology-engineering “double-track” system according to claim 2, wherein, in step S2, the geological evaluation index is calculated according to the following equation: $A=\frac{\left(\stackrel{\_}{e}-e_{\min }\right)}{\left(e_{\max }-e_{\min }\right)}$ Where, A is the geological evaluation index of the target horizontal fracturing interval, dimensionless; ē is an average reservoir property evaluation factor for all sampling sections, dimensionless; e.sub.max and e.sub.min are respectively maximum and minimum reservoir property evaluation factors in all sampling sections, dimensionless.

5. The method for the evaluation of the shale fracability under the geology-engineering “double-track” system according to claim 1, wherein, in step S3, the engineering evaluation index is calculated according to the following equation: $\frac{3}{f_i}=\frac{1}{C_i}+\frac{1}{P_{\mathrm{Fi}}}+\frac{1}{P_{\mathrm{Ti}}}$ Where, f.sub.i is the engineering evaluation index of the sampling section i, dimensionless; C.sub.i is the brittleness factor of the sampling section i based on the stress-strain curve, dimensionless; P.sub.Fi is the natural fracture factor of the sampling section i, dimensionless; P.sub.Ti is the natural fracture opening factor of the sampling section i, dimensionless.

6. The method for the evaluation of the shale fracability under the geology-engineering “double-track” system according to claim 5, wherein, in step S4, the engineering evaluation index is calculated according to the following equation: $B=\frac{\left(f-f_{\min }\right)}{\left(f_{\max }-f_{\min }\right)}$ Where, B is the engineering evaluation index of the target horizontal fracturing interval, dimensionless; f is an average engineering evaluation factor for all sampling sections, dimensionless; f.sub.max and f.sub.min are maximum and minimum engineering evaluation factors for all sampling sections, dimensionless.

7. The method for the evaluation of the shale fracability under the geology-engineering “double-track” system according to claim 1, wherein, in step S5, the shale fracability of the target horizontal fracturing interval is evaluated according to the geological evaluation index and the engineering evaluation index, specifically as follows: When the geological evaluation index is within the range of [0,0.1] and the engineering evaluation index is within the range of [0,1.0], the target horizontal fracturing interval is not fracturable; When the geological evaluation index is within a range of [0.1,1.0] and the engineering evaluation index is within the range of [0,1.0], the target horizontal fracturing interval is fracturable.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the following will make a brief introduction to the drawings needed in the description of the embodiments or the prior art. Obviously, the drawings in the following description are merely some embodiments of the present invention. For those of ordinary skill in the field, other drawings can be obtained based on the structures shown in these drawings without any creative effort.

(2) FIG. 1 is the process diagram of dynamic adjustment and optimization of fracturing construction scheme in the present invention;

(3) FIG. 2 is the production curve diagram of Well X in the present invention after fracturing in an embodiment;

(4) FIG. 3 is the production curve diagram of Well Y in the contrastive example after fracturing in an embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(5) The present invention is further described with reference to the drawings and embodiments. It should be noted that the embodiments in this application and the technical features in the embodiments can be combined with each other without conflict. It is to be noted that, unless otherwise specified, all technical and scientific terms herein have the same meaning as commonly understood by those of ordinary skill in the field to which this application belongs. “Include” or “comprise” and other similar words used in the present disclosure mean that the components or objects before the word cover the components or objects listed after the word and its equivalents, but do not exclude other components or objects.

(6) As shown in FIG. 1, the present invention provides a method for comprehensive evaluation of shale fracability under the geology-engineering “double-track” system, comprising the following steps:

(7) S1: Divide the target horizontal fracturing interval into multiple sampling sections.

(8) It should be noted that the target horizontal fracturing interval is divided into multiple sampling sections to mainly reduce the impact of reservoir heterogeneity on the accuracy of evaluation results. If the present invention is used to evaluate the fracability of homogeneous reservoirs, the target horizontal fracturing interval may not be divided into sections. In addition, when the horizontal fracturing interval is divided, the number of sections can be calculated according to the length of the horizontal fracturing interval, and all sampling sections can be numbered from downhole to wellhead. It should be noted that the division by length is only a preferred solution. The target horizontal fracturing interval can be also divided into several sections in the present invention according to other standards, such as the geological parameters of the horizontal fracturing interval.

(9) S2: Establish the reservoir property evaluation factor of each sampling section, and calculate the geological evaluation index of the target horizontal fracturing interval according to the reservoir property evaluation factor of each sampling section.

(10) In a specific embodiment, the reservoir property evaluation factor is calculated according to the following equations:
e.sub.i=a.sub.1ϕ.sub.i′+b.sub.1ω.sub.i′  (1)
a.sub.1+b.sub.1=1  (2)

(11) $\begin{array}{cc}{\varphi }_i^{\prime }=\frac{\left({\varphi }_{\mathrm{ie}}-{\varphi }_{\min }\right)}{\left({\varphi }_{\max }-{\varphi }_{\min }\right)}& \left(3\right)\end{array}$

(12) $\begin{array}{cc}{\omega }_i^{\prime }=\frac{\left({\omega }_i-{\omega }_{\min }\right)}{\left({\omega }_{\max }-{\omega }_{\min }\right)}& \left(4\right)\end{array}$

(13) Where, e.sub.i is the reservoir property evaluation factor of the sampling section i, dimensionless; a.sub.1 and b.sub.1 are the weight coefficients of physical properties, dimensionless; ϕ.sub.i′ is the porosity of the sampling section i, dimensionless; ω.sub.i′ is the total organic carbon content of the sampling section i, dimensionless; ϕ.sub.ie is the effective porosity of the sampling section i, %; ϕ.sub.max and ϕ.sub.min are respectively the maximum effective porosity and the minimum effective porosity in all sampling sections, %; ω.sub.i is the total organic carbon content of the sampling section i, %; ω.sub.max and ω.sub.min are respectively the maximum total organic carbon content and the minimum total organic carbon content in all sampling sections, %.

(14) Preferably, when the effective porosity of the target sampling section is greater than or equal to 4.5%, a.sub.1 and b.sub.1 are 0.65 and 0.35 respectively. When the effective porosity of the target sampling section is less than 4.5%, a.sub.1 and b.sub.1 are 0.55 and 0.45 respectively. It should be noted that the physical property weight coefficient of the present embodiment is the preferred physical property weight coefficient of the present invention according to the accuracy of the results, etc. In addition to the physical property weight coefficient of the present embodiment, other physical property weight coefficients can be also adopted according to the accuracy and other requirements.

(15) In a specific embodiment, the geological evaluation index is calculated according to the following equation:

(16) $\begin{array}{cc}A=\frac{\left(\stackrel{\_}{e}-e_{\min }\right)}{\left(e_{\max }-e_{\min }\right)}& \left(5\right)\end{array}$

(17) Where, A is the geological evaluation index of horizontal fracturing interval, dimensionless; ē is the average reservoir property evaluation factor for all sampling sections, dimensionless; e.sub.max and e.sub.min are respectively the maximum and minimum reservoir property evaluation factors in all sampling sections, dimensionless.

(18) S3: Establish the brittleness factor, natural fracture factor and natural fracture opening factor of each sampling section, and then establish the engineering evaluation index of each sampling section according to the brittleness factor, natural fracture factor and natural fracture opening factor of each sampling section.

(19) In a specific embodiment, the brittleness factor is calculated according to the following equations:

(20) $\begin{array}{cc}{C}_i=\lambda \left[1-\exp \left(\frac{M_i}{E_i}\right)\right]+\frac{\eta \left({\sigma }_{\mathrm{pi}}-{\sigma }_{\mathrm{ci}}\right)}{{\sigma }_{\mathrm{pi}}}& \left(6\right)\end{array}$
λ+η=1  (7)

(21) Where, C.sub.i is the brittleness factor of the sampling section i based on the stress-strain curve, dimensionless; λ and η are the standardized coefficients, dimensionless; M.sub.i is the softening modulus of the sampling section i, in GPa; E.sub.i is the elasticity modulus of the sampling section i, in GPa; σ.sub.pi is the peak strength obtained from the triaxial compression test at the sampling section i, in MPa; σ.sub.ci is the participating strength obtained from the triaxial compression test at the sampling section i, in MPa;

(22) The natural fracture factor is calculated according to the following equations.

(23) $\begin{array}{cc}{P}_{\mathrm{Fi}}=\frac{P_{\mathrm{fi}}-P_{f\min }}{P_{f\max }-P_{f\min }}& \left(8\right)\end{array}$

(24) $\begin{array}{cc}{P}_{\mathrm{fi}}=\frac{2E_i^2}{\left(K_{\mathrm{li}}^2+K_{2i}^2\right){\upsilon }_i}& \left(9\right)\end{array}$

(25) $\begin{array}{cc}{K}_{\mathrm{li}}=0.3172{\rho }_i+\frac{0.0457}{V_{\mathrm{ci}}}+0.2131\ln \left({\mathrm{DT}}_i\right)\times 0.5041& \left(10\right)\end{array}$

(26) 0$\begin{array}{cc}{K}_{2i}=2.1332{\rho }_i+\frac{0.0768}{V_{\mathrm{ci}}}+1.1886\ln \left({\mathrm{DT}}_i\right)\times 9.1808& \left(11\right)\end{array}$

(27) Where, P.sub.Fi is the natural fracture factor of the sampling section i, dimensionless; P.sub.fi is the representation number of natural fracture development degree in sampling section i, ×10.sup.6 m.sup.−1; P.sub.fmax and P.sub.fmin are respectively the maximum and minimum representation numbers of natural fracture development degree in all sampling sections, ×10.sup.6 m.sup.−1; K.sub.1i and K.sub.2i are respectively the Type I and Type II fracture toughness of the sampling section i, in MPa.Math.m.sup.0.5; ν.sub.i is the average static Poisson's ratio of the sampling section i, dimensionless; ρ.sub.i is the average shale density of the sampling section i, in g/cm.sup.3; V.sub.ci is the average mud content of the sampling section i, %; DT.sub.i is the average acoustic time difference of the sampling section i, in μs/m;

(28) The natural fracture opening factor is calculated according to the following equations:

(29) $\begin{array}{cc}{P}_{\mathrm{Ti}}=\frac{P_{t\max }-P_{\mathrm{ti}}}{P_{t\max }-P_{t\min }}& \left(12\right)\end{array}$
P.sub.ti=σ.sub.xil.sub.1i.sup.2+σ.sub.yil.sub.2i.sup.2+σ.sub.zil.sub.3i.sup.2+2τ.sub.xyil.sub.1il.sub.2i+2τ.sub.yzil.sub.2il.sub.3i+2τ.sub.zxil.sub.1il.sub.3i  (13)

(30) $\begin{array}{cc}{l}_{\mathrm{li}}=\sqrt{\frac{1-l_{3i}^2}{1+{\tan }^2{\theta }_i}}& \left(14\right)\end{array}$
l.sub.2i=l.sub.1i tan θ.sub.i  (15)
l.sub.3i=cos α.sub.i  (16)

(31) Where, P.sub.Ti is the natural fracture opening factor of the sampling section i, dimensionless; P.sub.ti is the fluid pressure when the natural fracture of the sampling section i is opened, in MPa; P.sub.tmax and P.sub.tmin are respectively the maximum and minimum fluid pressures in all sampling sections to meet the opening of natural fracture, in MPa; σ.sub.xi, σ.sub.yi and σ.sub.zi are respectively the normal stress, tangential normal stress and vertical stress of the shaft in the sampling section i, in MPa; l.sub.1i, l.sub.2i and l.sub.3i are respectively the cosine values of the included angle between the natural fracture and the maximum horizontal principal stress, minimum horizontal principal stress and vertical stress in the sampling section i, dimensionless; τ.sub.xyi, τ.sub.yzi and τ.sub.xzi are respectively the shear stress components of the sampling section i, in MPa; θ.sub.i is the included angle between the natural fracture and the direction of maximum horizontal principal stress in the sampling section i, °; α.sub.1 is the dip angle of natural fracture in the sampling section i, °.

(32) The engineering evaluation factor is calculated according to the following equation:

(33) $\begin{array}{cc}\frac{3}{f}=\frac{1}{C_i}+\frac{1}{P_{\mathrm{Fi}}}+\frac{1}{P_{\mathrm{Ti}}}& \left(17\right)\end{array}$

(34) Where, f.sub.i is the engineering evaluation factor of the sampling section i, dimensionless.

(35) It should be noted that the brittleness factor, natural fracture factor and natural fracture opening factor in Equation (17) of the present invention can be calculated by other calculation methods in the prior art in addition to the calculation equations shown in Equations (6)-(16).

(36) S4: Calculate the engineering evaluation index of the target horizontal fracturing interval according to the engineering evaluation factor of each sampling section.

(37) In a specific embodiment, the engineering evaluation index is calculated according to the following equation:

(38) $\begin{array}{cc}B=\frac{\left(\stackrel{\_}{f}-f_{\min }\right)}{\left(f_{\max }-f_{\min }\right)}& \left(18\right)\end{array}$

(39) Where, B is the engineering evaluation index of horizontal fracturing interval, dimensionless; f is the average engineering evaluation factor for all sampling sections, dimensionless; f.sub.max and f.sub.min are the maximum and minimum engineering evaluation factors for all sampling sections, dimensionless.

(40) S5: Evaluate the fracability of the target horizontal fracturing interval according to the geological evaluation index and the engineering evaluation index, specifically as follows:

(41) When the geological evaluation index is within the range of [0,0.1] and the engineering evaluation index is within the range of [0,1.0], the target horizontal fracturing interval is not fracturable.

(42) When the geological evaluation index is within the range of [0.1,1.0) and the engineering evaluation index is within the range of [0,1.0], the target horizontal fracturing interval is fracturable.

(43) In a specific embodiment, the method for comprehensive evaluation of shale fracability under the geology-engineering “double-track” system in the present invention further comprises the S6: Establish the fracturing construction scheme for the target horizontal fracturing interval according to the geological evaluation index and the engineering evaluation index. The specific fracturing construction scheme is shown in Table 1:

(44) TABLE-US-00001 TABLE 1 Fracturing construction scheme for target horizontal fracturing interval under different geological evaluation indexes and engineering evaluation indexes Geo- logical evaluation Engineering evaluation index B index A [0, 0.3] (0.3, 0.7] (0.7, 1.0] [0, 0.1] Abandoned (0.1, 0.4] Slickwater Slickwater Slickwater fracturing + fracturing + fracturing fiber temporary fiber temporary plugging and plugging diverting and diverting (0.4, 0.7] Large-scale Large-scale Slickwater fracturing + fiber fracturing + fracturing + temporary plugging fiber temporary fiber and diverting + plugging temporary medium multi- and diverting plugging and clustered volume diverting fracturing (0.7, 1.0] Large-scale Large-scale Large-scale fracturing + fiber fracturing + fracturing + temporary plugging fiber fiber and diverting + temporary temporary highly multi- plugging plugging and clustered volume and diverting fracturing diverting + medium multi-clustered volume fracturing

(45) In a specific embodiment, in Table 1, the slickwater formula for slickwater fracturing is 0.2% effective drag reducer FJZ-2+0.5% polymer emulsion viscosifier FZN-1+0.25% anti-water lock surfactant FSSJ-8+100 KCl, the construction displacement is 16-18 m.sup.3/min, and the liquid intensity is 28-30 m.sup.3/m. The specific displacement and consumption are calculated according to the pumping equipment and the construction length of the horizontal interval (the calculation method is the prior art and will not be described here). It should be noted that slickwater fracturing technology is a prior art. In addition to the slickwater formula used in this embodiment, other slickwater formulas in the prior art can be also used depending on the formation conditions of the target well.

(46) The large-scale fracturing means that the liquid intensity for fracturing is 150% of that for slickwater fracturing, and the other parameters are the same as those for slickwater fracturing. The fiber temporary plugging and diverting means that the fiber is added when the slickwater pumping pressure is stable until the pumping pressure is increased by 6-10 MPa; the fiber length is 5.00-6.00 mm, the fiber concentration is 0.5-1.8%, the fiber consumption is calculated according to the on-site construction conditions (the calculation method is the prior art, which will not be described here). The cluster spacing corresponding to the medium multi-clustered volume fracturing and the highly multi-clustered volume fracturing is 12 m and 10 m, and the perforating density is 4 shots/cluster and 6 shots/cluster respectively. For other fracturing construction schemes, the cluster spacing is 14 m, and the perforating density is 4 shots/cluster. The perforating depth is 0.2 m, and the number of clusters is calculated according to the length of the fracturing interval (the calculation method is the prior art, which will not be described here).

(47) Two adjacent horizontal wells X and Y in shale gas reservoir in southern Sichuan are taken as examples to verify the accuracy of the method for comprehensive evaluation of shale fracability under the geology-engineering “double-track” system in the present invention. The horizontal interval length of Well X and Well Y are 1,080 m and 1,260 m respectively. The geological exploration results show that the shale gas reserves in the reservoir where the two horizontal intervals are located are high, but the brittleness index is poor. According to the horizontal well development experience in this area, Well X and Well Y are subject to stimulation by staged and clustered fracturing in a horizontal well with a section length of 60 m, and the number of sections is 18 and 21 respectively. The cluster spacing is 12 m, the number of clusters is 5; the perforating density is 4 shots/cluster, and the perforating depth is 0.2 m; the slickwater pumping displacement is 16 m.sup.3/min, the average amount of liquid used per section is 1,800 m.sup.3, and the total amount is 3.24×10.sup.4 m.sup.3 and 3.78×10.sup.4 m.sup.3 respectively.

(48) The present invention is adopted for the fracability evaluation of Well X, specifically as follows:

(49) (1) Divide the horizontal interval from toe end to heel end every 10 m and number it;

(50) (2) According to the core laboratory evaluation experiment data, count the total organic carbon content, porosity and effective porosity of each sampling section, and obtain the reservoir property evaluation factor of each sampling section based on the Equations (1)-(4);

(51) (3) Obtain the geological evaluation index of each target fracturing interval of Well X based on the Equation (5) according to the reservoir property evaluation factor of each sampling section;

(52) (4) Obtain other basic data of each sampling section by analyzing the mineral composition, sorting out the logging data, measuring the core mechanical parameters, establishing the numerical model and through data fitting and regression, etc. Obtain the brittleness factor, natural fracture factor and natural fracture opening factor of each sampling section based on the Equations (6)-(16);

(53) (5) Obtain the engineering evaluation index of each target fracturing interval based on the Equation (17) according to the brittleness factor, the natural fracture factor and the natural fracture opening factor of each sampling section;

(54) (6) According to the geological evaluation index obtained from Step (3) and the engineering evaluation index obtained from Step (5), carry out the dynamic adjustment and optimization of fracturing construction scheme for Well X in combination with FIG. 1, with the results shown in Table 2.

(55) It should be noted that, in Step (6), the dynamic adjustment and optimization method shown in FIG. 1 is taken for the staged fracturing of target fracturing interval so as to improve the final fracturing effect. In use, it can be also staged directly according to the section length as required, and then according to the geological evaluation index and engineering evaluation index results of each section, the fracturing construction scheme of each section can be formulated in combination with Table 1.

(56) TABLE-US-00002 TABLE 2 Suggestions for fracturing construction scheme of Well X Geological Engineering Section Measured Section evaluation evaluation No. depth length index index k m m A.sub.k B.sub.k Fracturing construction scheme 1  5420- 70 0.605 0.470 Large-scale fracturing + fiber temporary plugging and 5490 diverting 2  5360- 60 0.415 0.263 Large-scale fracturing + fiber temporary plugging and 5420 diverting + medium multi-clustered volume fracturing 3  5290- 70 0.217 0.294 Slickwater fracturing + fiber temporary plugging and 5360 diverting 4  5240- 50 0.809 0.281 Large-scale fracturing + fiber temporary plugging and 5290 diverting + highly multi-clustered volume fracturing 5  5160- 70 0.391 0.439 Slickwater fracturing + fiber temporary plugging and 5230 diverting 6  5090- 70 0.582 0.596 Large-scale fracturing + fiber temporary plugging and 5160 diverting 7  5030- 60 0.805 0.372 Large-scale fracturing + fiber temporary plugging and 5090 diverting + medium multi-clustered volume fracturing 8  4980- 50 0.759 0.225 Large-scale fracturing + fiber temporary plugging and 5030 diverting + highly multi-clustered volume fracturing 9  4930- 50 0.795 0.219 Large-scale fracturing + fiber temporary plugging and 4980 diverting + highly multi-clustered volume fracturing 10  4860- 60 0.731 0.554 Large-scale fracturing + fiber temporary plugging and 4920 diverting + medium multi-clustered volume fracturing 11  4790- 70 0.532 0.387 Large-scale fracturing + fiber temporary plugging and 4860 diverting 12  4720- 70 0.388 0.405 Slickwater fracturing + fiber temporary plugging and 4790 diverting 13  4640- 70 0.583 0.701 Slickwater fracturing + fiber temporary plugging and 4710 diverting 14  4580- 60 0.706 0.644 Large-scale fracturing + fiber temporary plugging and 4640 diverting + medium multi-clustered volume fracturing 15  4510- 70 0.643 0.476 Large-scale fracturing + fiber temporary plugging and 4580 diverting 16  4460- 50 0.793 0.256 Large-scale fracturing + fiber temporary plugging and 4510 diverting + highly multi-clustered volume fracturing

(57) In Table 2, the construction amount of slickwater for slickwater fracturing is 31,200 m.sup.3, the pumping displacement is 16 m.sup.3/min, and the total amount of slickwater is 3.12×10.sup.4 m.sup.3. The fiber concentration for fiber temporary plugging and diverting is 1%, the fiber length is 6 mm, and the fiber dosage is 7 t. The cluster spacing for medium multi-clustered volume fracturing is 12 m, and the perforating density is 4 shots/cluster. The cluster spacing for highly multi-clustered volume fracturing is 10 m, and the perforating density is 6 shots/cluster. The cluster spacing of other sections is 14 m, and the perforating density is 4 shots/cluster. The perforating depth is 0.2 m.

(58) According to the fracturing construction scheme suggested in Table 2, the production curve of Well X after fracturing is obtained, with results shown in FIG. 2. Seen from FIG. 2, the maximum daily gas output of Well X is 26.1×10.sup.4 m.sup.3 at the initial stage of construction, and the average daily gas output is 15.1×10.sup.4 m.sup.3 in the first year and 11.5×10.sup.4 m.sup.3 in the second year.

(59) For Well Y adjacent to Well X, the original fracturing design scheme (the above fracturing scheme formulated depending on the experience of horizontal well development) is adopted for fracturing construction, and the production curve of Well Y after fracturing is obtained, with results shown in FIG. 3. On the one hand, the real-time detection of microseism shows that if compared with Well X, the distribution of fracture network in Well Y reservoir is poor and the oil and gas reservoir body is not effectively communicated. On the other hand, it can be seen from FIG. 3 that the maximum daily gas output in Well Y is 23.3×10.sup.4 m.sup.3, and the average daily gas output is 13.1×10.sup.4 m.sup.3 in the first year and 8.2×10.sup.4 m.sup.3 in the second year. Therefore, the fracturing construction scheme of shale reservoir, which is put forward through parallel consideration of geological factors and engineering factors in the present invention, is more reasonable. It can effectively optimize the distribution of reservoir fracture network, increase the effective cover area of fracture network, and stably improve the production capacity of single well for a long time. It has a certain guiding significance for the efficient and low-cost development of shale reservoirs. If compared with the prior art, the present invention has significant progress.

(60) The above are not intended to limit the present invention in any form. Although the present invention has been disclosed as above with embodiments, it is not intended to limit the present invention. Those skilled in the field, within the scope of the technical solution of the present invention, can use the disclosed technical content to make a few changes or modify the equivalent embodiment with equivalent changes. Within the scope of the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention are still regarded as a part of the technical solution of the present invention.