Comprehensive evaluation method for dessert of shale reservoir

Abstract

The invention relates to the technical field of geological exploration, in particular to a comprehensive evaluation method for desserts of a shale reservoir. The method comprises the following steps: dividing a shale reservoir target evaluation section into a plurality of units, carrying out continuous coring work on each unit, carrying out pretreatment, and testing physical property parameters and mineral components of a pretreated rock sample; calculating a rock reservoir capacity index, and quantitatively evaluating the geological sweet spots of the reservoir; and calculating a rock fracture complex potential index, quantitatively evaluating the engineering dessert of the reservoir, and coupling the rock reservoir capacity index and the fracture complex potential index to calculate the dessert index. According to the method, a traditional shale dessert evaluation method is redefined, enrichment optimization and productivity maximization are pursued at the same time, and the defect that reservoir parameters or engineering parameters are purely considered in the past is overcome. The calculation method is simple and feasible, the economic cost is greatly reduced, and the method is also suitable for comprehensive evaluation of similar unconventional reservoir desserts, has a good application prospect and has a good guiding effect on exploration and development of unconventional resources.

Description

Technical Field

[0001] The invention relates to the technical field of geological exploration, and in particular to a comprehensive evaluation method for shale reservoir sweet spots. Background Art

[0002] Horizontal well volume fracturing technology has realized the commercial development of unconventional shale oil and gas, accelerated the energy independence of the United States, and pushed the wave of energy revolution to the world. China's shale oil and gas resources are also extremely rich, mainly distributed in large basins such as Ordos, Junggar, Songliao, Bohai Bay, and Sichuan Basin. They have huge development potential and have become the most strategic oil replacement resources. However, with the shift to unconventional resource exploration and development, volume fracturing technology and reservoir matching face many challenges. The next step of technology optimization and improvement is the key to reducing costs and increasing efficiency. Among them, finding a favorable "sweet spot area" is the core goal of exploration and development, the key to achieving a breakthrough in single well production, and the basis for horizontal well volume fracturing optimization. However, there are many factors that affect the identification of unconventional shale oil and gas sweet spots and the relationship is complex. Domestic and foreign scholars have done a lot of research on the evaluation and division of sweet spots, but none of them considers the integrated comprehensive evaluation of geological and engineering sweet spots at the same time, ultimately guiding the optimization design of fracturing and evaluating the risk of engineering construction. Therefore, it is necessary to propose a new comprehensive evaluation method for shale reservoir sweet spots to provide important theoretical support for the efficient development of unconventional resources.

[0003] The prior art provides a method for quantitative evaluation of engineering sweet spots based on parameter optimization, patent number: CN201710208633.5. The method uses the correlation between engineering sweet spot parameters and sand carrying ratio to determine the main engineering sweet spot parameters, and uses the independence weight coefficient method to determine the weight of each of the main engineering sweet spot parameters; based on the weight of the main engineering sweet spot parameters, the engineering sweet spot coefficient of the shale formation expressed by the weight is calculated; according to the engineering sweet spot coefficient, the engineering sweet spot of the shale formation is quantitatively evaluated, and the main evaluation basis of this method is to obtain the weight coefficient of the engineering parameter.

[0004] In actual applications, it was found that this method only considers the engineering parameters of rocks and uses weight coefficients to obtain the correlation with engineering sweet spots. This method is a feasible method for obtaining engineering parameters, but this method considers fewer factors. At the same time, for unconventional reservoirs, it is necessary to pursue the integration of geology and engineering sweet spots, and the geological sweet spots have not yet been considered.

[0005] Another prior art discloses a method and system for predicting sweet spots in shale reservoir lithofacies, patent number: CN202110232294.0. This method obtains attribute parameters related to oil production per meter based on the intersection relationship between the attribute parameters of the shale reservoir lithofacies and the daily oil production per meter, and establishes a comprehensive evaluation model of sweet spots based on the attribute parameters to intuitively evaluate the quality of the reservoir. However, this method only considers the influencing factors of geological sweet spots and ignores engineering factors. Summary of the invention

[0006] 1. Technical issues to be resolved

[0007] The present invention provides a comprehensive evaluation method for shale reservoir sweet spots to overcome the defects of the methods used in the prior art that cannot take into account both the geological and engineering factors of shale sweet spots, resulting in the lack of unconventional shale oil and gas production capacity maximization goals and engineering construction feasibility, resulting in complex calculation methods and high economic costs.

[0008] (II) Technical solution

[0009] In order to solve the above problems, the present invention provides a comprehensive evaluation method for shale reservoir sweet spots, which specifically includes:

[0010] Step S1, dividing the target evaluation section of the shale reservoir into several units, carrying out continuous coring work on each unit, and performing pretreatment, and testing the physical property parameters and mineral composition of the pretreated rock samples;

[0011] Step S2, calculating the rock storage capacity index according to the physical property parameters of the tested rock sample, and quantitatively evaluating the geological sweet spot of the reservoir;

[0012] Step S3, calculating the rock fracture complexity potential index according to the mineral composition of the tested rock sample, and quantitatively evaluating the engineering sweet spot of the reservoir;

[0013] Step S4, the rock storage capacity index and the fracture complexity potential index are coupled to calculate the sweet spot index, and the sweet spot index is interpreted. The larger the value of the sweet spot index is, the better the reservoir geology and engineering sweet spot is, and the greater the potential for obtaining high production capacity after volume fracturing, thereby achieving the purpose of comprehensive evaluation of the shale reservoir sweet spot.

[0014] Preferably, the pretreatment in step S1 includes: placing in an oven at 100° C. and drying to constant weight.

[0015] Preferably, step S2 comprises: using a helium porosity automatic tester and an ultra-low permeability tester to test the porosity of the dried rock sample respectively. and permeability k, and the relationship between porosity and permeability is used to calculate the reservoir capacity index I of the rock sample R , quantitatively evaluate reservoir geological sweet spots.

[0016] Preferably, step S3 includes testing the mineral composition of the dried rock sample using an X-ray diffractometer.

[0017] Preferably, the storage capacity index I of the rock sample is calculated R The formulas include:

[0018]

[0019] Where: I R is the rock sample storage capacity index, μm 2 ; k is the permeability of the rock sample, μm 2 ; is the porosity of the rock sample, %.

[0020] Preferably, step S3 specifically includes:

[0021] The mineral content test results of shale samples are used to calculate the fracture complexity potential index, classify the micro-fracture levels, evaluate the reservoir's ability to form a fracture network, and classify shale reservoirs:

[0022] Step S31: Calculate the percentage of different mineral masses according to the test results of different mineral components of shale samples in the target shale section. The calculation formula is as follows:

[0023]

[0024] Where: i is the number of different minerals in shale samples, dimensionless; Q is the mass percentage of different minerals in shale samples, %; M is the mass of different minerals in shale samples, g;

[0025] Step S32: Calculate the uniformity coefficient according to the percentage of different mineral masses and the number of mineral types in the shale sample. The calculation formula is as follows:

[0026]

[0027] Where: G is the uniformity coefficient, %; n is the number of mineral species in the shale sample, species;

[0028] Step S33: Calculate the heterogeneity D according to the mass percentages and uniformity coefficients of different minerals in the shale sample. Its physical meaning is the sum of the absolute values ​​of the differences between the percentages of each mineral and the uniformity coefficient G. The calculation formula is as follows:

[0029]

[0030] Where: i is the number of different minerals in the shale sample, dimensionless; D is the heterogeneity of different minerals, dimensionless; Q is the percentage of different minerals, %;

[0031] Step S34: Calculate the maximum value D of the heterogeneity of different minerals max With the minimum value D min , when there is only one mineral in the rock sample, its inhomogeneity reaches the maximum; when the mineral components in the rock sample are evenly distributed, its inhomogeneity is the minimum. The calculation expression is as follows:

[0032]

[0033]

[0034] Step S35: Calculate the crack complexity potential index B, set the value range of the crack complexity potential index between 0 and 1, and the calculation formula of the crack complexity potential index B is as follows:

[0035]

[0036] Where: B is the fracture complexity potential index; D is the mineral heterogeneity.

[0037] Preferably, step S4 comprises:

[0038] Step S41: Storage capacity index I for rock R The maximum and minimum values ​​are calculated, and the calculation formula is as follows for the limit analysis of the tested rock sample:

[0039]

[0040]

[0041] Where: k max is the maximum permeability under the rock properties, μm 2 ;k min is the minimum permeability under the rock properties, μm 2 ; is the maximum porosity under the rock properties, %; is the minimum porosity under the rock properties, %;

[0042] Step S42: quantitatively evaluate the sweet spot of the formation by combining the physical properties of the rock and the fracture complexity potential index. The calculation formula is as follows:

[0043]

[0044] Where: Z is the shale sweet spot index, dimensionless; (I R ) max with(I R ) min Theoretical maximum and minimum rock sample storage capacity index for this type of rock, μm 2 .

[0045] (III) Beneficial effects

[0046] The present invention provides a comprehensive evaluation method for shale reservoir sweet spots. The method considers the geological and engineering factors that affect shale sweet spots at the same time, and defines a new sweet spot index for integrated comprehensive quantitative characterization of geological and engineering sweet spots. The method redefines the traditional shale sweet spot evaluation method, and pursues enrichment optimization and production capacity maximization at the same time, making up for the previous simple consideration of reservoir parameters or engineering parameters, while ignoring the goal of maximizing the production capacity of unconventional shale oil and gas and the feasibility of engineering construction. The calculation method is simple and feasible, greatly reducing the economic cost, and is also applicable to the comprehensive evaluation of similar unconventional reservoir sweet spots. It has good application prospects and has a good guiding role in the exploration and development of unconventional resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is a comparison chart of the storage capacity index of shale samples;

[0048] Figure 2 This is a comparison chart of fracture complexity potential index of shale samples;

[0049] Figure 3 Sweet spot index ranking diagram for shale samples;

[0050] Figure 4 This is a flow chart of a comprehensive evaluation method for shale reservoir sweet spots according to an embodiment of the present invention; DETAILED DESCRIPTION

[0051] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0052] like Figure 4 As shown, the present invention provides a comprehensive evaluation method for shale reservoir sweet spots, which specifically includes the following steps:

[0053] Step S1, dividing the target evaluation section of the shale reservoir into several units, carrying out continuous coring work on each unit, and performing pretreatment, and testing the physical property parameters and mineral composition of the pretreated rock samples;

[0054] Step S2, calculating the rock storage capacity index according to the physical property parameters of the tested rock sample, and quantitatively evaluating the geological sweet spot of the reservoir;

[0055] Step S3, calculating the rock fracture complexity potential index according to the mineral composition of the tested rock sample, and quantitatively evaluating the engineering sweet spot of the reservoir;

[0056] Step S4, the rock storage capacity index and the fracture complexity potential index are coupled to calculate the sweet spot index, and the sweet spot index is interpreted. The larger the value of the sweet spot index is, the better the reservoir geology and engineering sweet spot is, and the greater the potential for obtaining high production capacity after volume fracturing, thereby achieving the purpose of comprehensive evaluation of the shale reservoir sweet spot.

[0057] The following describes in detail the specific implementation of the present invention based on the accompanying drawings and a downhole core of a certain block as an example. The details are as follows:

[0058] (1) Rock sample preparation: The actual downhole cores of shale gas wells were taken at a depth of 2540-2500 m, and five standard rock samples with a diameter of 2.5 cm and a length of 5 cm were prepared. The rock samples were numbered S1-S5 and dried in an oven at 100 °C to constant weight, as shown in Table 1.

[0059] Table 1 Basic parameters of shale samples

[0060]

[0061] (2) Calculation of shale reservoir capacity index: The porosity of the rock sample after drying described in step (1) is measured using a helium porosity automatic tester and an ultra-low permeability tester. and permeability k, see Table 1, and use formula (1) to calculate the reservoir capacity index I of the rock sample R , quantitatively evaluate the reservoir geological sweet spot. The calculation results are shown in Table 1 and Appendix Figure 1 .

[0062] (3) Shale mineral content test: The mineral composition of the rock sample in step S2 was tested using an X-ray diffractometer. The test results are shown in Table 2.

[0063] Table 2 Mineral composition of shale samples

[0064]

[0065] (4) Calculation of rock fracture complexity potential index: The rock fracture complexity potential index is calculated using the test results of the mineral content of shale samples to evaluate the reservoir volume fracturing capacity to form a fracture network, and then evaluate the engineering sweet spots of the shale reservoir, which specifically includes the following:

[0066] ① According to the test results of different mineral components of the core of the shale target section, the formula Calculate the percentage content of different mineral masses and divide the shale mineral composition table in Table 2 into percentages of mineral types, as shown in Table 3.

[0067] Table 3 Mineral composition of shale samples

[0068]

[0069]

[0070] ② Calculate the uniformity coefficient according to the percentage of different mineral masses and the number of mineral types in the shale sample, using the formula Here n is equal to 6, so G = 16.67%.

[0071] ③ According to the percentage content and uniformity coefficient of different mineral masses in shale samples, calculate the unevenness D using the formula The calculation results are shown in Table 4.

[0072] Table 4 Calculation results of rock sample unevenness

[0073]

[0074] ④Use the formula Calculation of the maximum value Dmax of different mineral heterogeneity and formula Calculate the minimum value D min , we get D max =1.67, D min =0.27.

[0075] ⑤Use the formula The calculation results of the crack complexity potential index B, with B=-0.6D+1.16, are shown in Table 5.

[0076] Table 5 Results of fracture complexity potential index of shale samples

[0077]

[0078]

[0079] (5) Calculation of shale sweet spot index: Combined with the rock storage capacity index I R and rock fracture complexity potential index B, and calculate the sweet spot index.

[0080] ① Rock storage capacity index I R The maximum and minimum values ​​of and At present, the target rock samples are all shale, so (I R ) max =0.0005, (I R ) min =0.

[0081] ② Combine the physical properties of the rock and the fracture complexity potential index to quantitatively evaluate the sweet spot of the formation. The calculation formula is as follows: Substitute the data and get Z = 2000I R B, the data are shown in Table 6, and the intuitive expression is as follows Figure 1, Figure 2 and Figure 3 shown.

[0082] Table 6 Calculation diagram of sweet spot index of shale samples

[0083]

[0084] The present invention provides a comprehensive evaluation method for shale reservoir sweet spots. The method first divides the target evaluation section of the shale reservoir into several units, conducts continuous coring work on each unit, and tests the physical parameters and mineral composition of the rock samples. Secondly, the rock storage capacity index is calculated according to the physical parameters of the tested rock samples to quantitatively evaluate the geological sweet spots of the reservoir. On this basis, the rock fracture complexity potential index is calculated according to the rock mineral composition to quantitatively evaluate the engineering sweet spots of the reservoir. Finally, the rock storage capacity index and the fracture complexity potential index are coupled to calculate the sweet spot index. The larger the value, the better the reservoir geology and engineering sweet spots, and the greater the potential for obtaining high production capacity after volume fracturing, thereby achieving the purpose of comprehensive evaluation of the shale reservoir sweet spots.

[0085] The above implementation modes are only used to illustrate the present invention, but not to limit the present invention. Ordinary technicians in the relevant technical field can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions also belong to the scope of the present invention. The patent protection scope of the present invention should be defined by the claims.

Claims

1. A comprehensive evaluation method for shale reservoir sweet spots, characterized in that: include: Step S1, dividing the target evaluation section of the shale reservoir into several units, carrying out continuous coring work on each unit, and performing pretreatment, and testing the physical property parameters and mineral composition of the pretreated rock samples; Step S2, calculating the rock storage capacity index according to the physical property parameters of the tested rock sample, and quantitatively evaluating the geological sweet spot of the reservoir; Step S3, calculating the rock fracture complexity potential index according to the mineral composition of the tested rock sample, and quantitatively evaluating the engineering sweet spot of the reservoir; Step S4, coupling the rock storage capacity index with the fracture complexity potential index to calculate the sweet spot index; Evaluation is performed based on the sweet spot index: the larger the value of the sweet spot index is, the better the reservoir geology and engineering sweet spots are, and the greater the potential for obtaining high production capacity after volume fracturing, thereby achieving the purpose of comprehensive evaluation of the shale reservoir sweet spots.

2. The comprehensive evaluation method for shale reservoir sweet spots according to claim 1, characterized in that: The pretreatment in step S1 includes: placing in a 100° C. oven for drying to constant weight.

3. The comprehensive evaluation method for shale reservoir sweet spots according to claim 2, characterized in that: The step S2 comprises: using a helium porosity automatic tester and an ultra-low permeability tester to test the porosity of the dried rock sample respectively. and permeability k, and the relationship between porosity and permeability is used to calculate the reservoir capacity index I of the rock sample R , quantitatively evaluate reservoir geological sweet spots.

4. The comprehensive evaluation method for shale reservoir sweet spots according to claim 2, characterized in that: The step S3 includes testing the mineral composition of the dried rock sample using an X-ray diffractometer.

5. The comprehensive evaluation method for shale reservoir sweet spots according to claim 3, characterized in that: Calculate the storage capacity index I of the rock sample R The formulas include: Where: I R is the rock sample storage capacity index, μm 2 ; k is the permeability of the rock sample, μm 2 ; is the porosity of the rock sample, %.

6. The comprehensive evaluation method for shale reservoir sweet spots according to claim 3, characterized in that: Step S3 specifically includes: The mineral content test results of shale samples are used to calculate the fracture complexity potential index, classify the micro-fracture levels, evaluate the reservoir's ability to form a fracture network, and classify shale reservoirs: Step S31: Calculate the percentage of different mineral masses according to the test results of different mineral components of shale samples in the target shale section. The calculation formula is as follows: Where: i is the number of different minerals in shale samples, dimensionless; Q is the mass percentage of different minerals in shale samples, %; M is the mass of different minerals in shale samples, g; Step S32: Calculate the uniformity coefficient according to the percentage of different mineral masses and the number of mineral types in the shale sample. The calculation formula is as follows: Where: G is the uniformity coefficient, %; n is the number of mineral species in the shale sample, species; Step S33: Calculate the heterogeneity D according to the mass percentages and uniformity coefficients of different minerals in the shale sample. Its physical meaning is the sum of the absolute values ​​of the differences between the percentages of each mineral and the uniformity coefficient G. The calculation formula is as follows: Where: i is the number of different minerals in the shale sample, dimensionless; D is the heterogeneity of different minerals, dimensionless; Q is the percentage of different minerals, %; Step S34: Calculate the maximum value D of the heterogeneity of different minerals max With the minimum value D min When there is only one mineral in the rock sample, its inhomogeneity reaches the maximum; when the mineral components in the rock sample are evenly distributed, its inhomogeneity is the minimum. The calculation expression is as follows: Step S35: Calculate the crack complexity potential index B, set the value range of the crack complexity potential index between 0 and 1, and the calculation formula of the crack complexity potential index B is as follows: Where: B is the fracture complexity potential index; D is the mineral heterogeneity.

7. The comprehensive evaluation method for shale reservoir sweet spots according to claim 1, characterized in that: The step S4 comprises: Step S41: Storage capacity index I for rock R The maximum and minimum values ​​are calculated, and the calculation formula is as follows for the limit analysis of the tested rock sample: Where: k max is the maximum permeability under the rock properties, μm 2 ;k min is the minimum permeability under the rock properties, μm 2 ; is the maximum porosity under the rock properties, %; is the minimum porosity under the rock properties, %; Step S42: quantitatively evaluate the sweet spot of the formation by combining the physical properties of the rock and the fracture complexity potential index. The calculation formula is as follows: Where: Z is the shale sweet spot index, dimensionless; (I R ) max with(I R ) min Theoretical maximum and minimum rock sample storage capacity index for this type of rock, μm 2 .

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