阅读说明：本技术 一种改进的基于矿物组成的页岩脆性指数确定方法 (Improved shale brittleness index determination method based on mineral composition ) 是由 马存飞 蒲秀刚 韩文中 杜争利 于 2019-09-11 设计创作，主要内容包括：本发明公开了一种改进的基于矿物质组成的页岩脆性指数确定方法,该方法包括通过干酪根镜鉴识别待测页岩中干酪根类型,通过有机碳分析确定页岩中总有机碳含量W<Sub>o</Sub>；计算有机质体积分数V<Sub>o</Sub>,进而求得有机质体积含量V<Sub>organic</Sub>；通过X衍射全岩矿物分析确定页岩中长英质矿物含量W<Sub>flesic</Sub>、碳酸盐矿物含量W<Sub>carbonate</Sub>、黏土矿物含量W<Sub>clay</Sub>和无机矿物含量总和V<Sub>im</Sub>,进行归一化处理求得碳酸盐矿物体积含量V<Sub>carbonate</Sub>、长英质矿物体积含量V<Sub>flesic</Sub>和黏土矿物体积含量V<Sub>carbonate</Sub>,得出计算改进的基于矿物组成的页岩脆性指数B<Sub>rit</Sub>,该方法既可以体现碳酸盐矿物质对页岩可压性的双重作用,又提高了页岩脆性指数的精准度。(The invention discloses an improved shale brittleness index determination method based on mineral composition, which comprises the steps of identifying the type of a dry kerogen in shale to be detected through kerogen microscopy, and determining the total organic carbon content W in the shale through organic carbon analysis o (ii) a Calculating the organic matter volume fraction V o Further, the volume content V of the organic matter is obtained organic (ii) a Determination of the content W of long-grained minerals in shale by X-ray diffraction Whole rock mineral analysis flesic Carbonate mineral content W carbonate Clay mineral content W clay And the sum of the inorganic mineral contents V im And carrying out normalization treatment to obtain the volume content V of carbonate minerals carbonate Long-grained and long-grained mineralsVolume content V flesic And clay mineral volume content V carbonate Obtaining shale brittleness index B based on mineral composition rit The method not only can reflect the dual functions of carbonate minerals on the compressibility of the shale, but also improves the precision of the brittleness index of the shale.)

1. An improved shale brittleness index determination method based on mineral composition, comprising:

s11, identifying the type of the cheese root in the shale to be detected through a kerogen scope; the kerogen types are I type, II type and III type;

s12 determination of total organic carbon content W in shale by organic carbon analysis_o；

S13, determining a conversion coefficient K according to the type of the kerogen and the evolution stage, and determining the total organic carbon content W according to the total organic carbon content_oThe conversion coefficient K and the organic matter density rho_oAnd rock density ρ_mCalculating the organic matter volume fraction V_oAnd converted into organic matter volume content V_organic；

S14 determination of content W of long-grained quartz minerals in shale by X-ray diffraction whole-rock mineral analysis_flesicCarbonate mineral content W_carbonateClay mineral content W_clayAnd the sum of the inorganic mineral contents V_im；

S15, according to the organic matter volume content V_organicThe sum of the mineral contents of the inorganic substances V_imSaid carbonate mineral content W_carbonateSaid long EnglishMass mineral content W_flesicAnd the clay mineral content W_clayCarrying out normalization treatment to obtain the volume content V of carbonate minerals_carbonateVolume content of long-grained and long-grained minerals V_flesicAnd clay mineral volume content V_clay；

S16, according to the organic matter volume content V_organicThe volume content V of carbonate mineral_carbonateThe volume content V of the long-grained quartz minerals_flesicAnd the clay mineral volume content V_clayObtaining shale brittleness index B based on mineral composition_rit。

2. The improved shale brittleness index determination method based on mineral composition as claimed in claim 1, wherein the step S12 includes:

removing inorganic carbon from the shale sample to be tested by using dilute hydrochloric acid, and converting the organic carbon into CO by combustion oxidation in high-temperature oxygen flow₂Detection of CO using a detector₂The total organic carbon content W is calculated_o。

3. The improved shale brittleness index determination method based on mineral composition as claimed in claim 1, wherein the step S13 includes:

volume fraction of organic matter V_oThe formula of (1) is:

V_o＝W_o×K×ρ_m/ρ_o；

(4)

wherein, V_oIs the organic matter volume fraction; w_oIs the total organic carbon content; k is an organic matter conversion coefficient; rho_mThe shale density is 2.5g/cm³；ρ_oThe organic matter density is 1.0g/cm³；

From V_organic＝V_o×V_mCalculating the volume content V of organic matter_organic。V_mFor the entire shale sample volume, consider 1。

4. The improved shale brittleness index determination method based on mineral composition according to claim 3, wherein the transformation coefficient K of different types of kerogen is different in value at different evolution stages;

the value of the type I kerogen in the diagenesis stage is 1.25, and the value of the type I kerogen in the final stage of the deep diagenesis stage is 1.2;

the value of the type II kerogen is 1.34 in the diagenesis stage and 1.19 in the final stage of the deep diagenesis stage;

the value of the type III kerogen in the diagenesis stage is 1.48, and the value of the type III kerogen in the late stage of the deep diagenesis stage is 1.18.

5. The improved shale brittleness index determination method based on mineral composition as claimed in claim 1, wherein the step S14 includes:

grinding the shale sample to be detected into 200-mesh powder, placing the powder in a sample chamber of an X-ray diffraction instrument for X-ray scanning and mineral analysis to respectively obtain the content W of carbonate minerals_carbonateLong-grained and long-grained minerals content W_flesicClay mineral content W_clayAnd the sum of the inorganic mineral contents V_im。

6. The improved shale brittleness index determination method based on mineral composition as claimed in claim 1, wherein the step S15 includes:

volume content of long-grained and British minerals V_flesic＝W_flesic/V_im×(V_m-V_organic)；

Volume content of carbonate mineral is V_carbonate＝W_carbonate/V_im×(V_m-V_organic)；

Clay mineral volume content of V_clay＝W_clay/V_im×(V_m-V_organic)。

7. The improved shale brittleness index determination method based on mineral composition as claimed in claim 5, wherein the step S16 includes:

the formula of the shale brittleness index is as follows:

B_rit＝(V_flesic+V_carbonate)/(V_clay+V_flesic+V_carbonate+V_organic)；

(5)

the value obtained in the S15 and the organic matter volume content V in the S13 are compared_organicSubstituting into a formula to obtain a shale brittleness index B_rit。

Technical Field

The invention relates to the technical field of geological exploration, in particular to an improved shale brittleness index determination method based on mineral composition.

Background

Rock mineral composition has a great influence on the reformation of shale, and the traditional shale brittleness index calculation method based on mineral composition has three types:

(1)B_rit＝V_quartz/(V_quartz+V_carbonate)*100，

(2)B_rit＝V_felsic/(V_felsic+V_carbonate)*100，

(3)B_rit＝(V_felsic+V_carbonate)/(V_felsic+V_carbonate+V_clay)*100。

carbonate minerals have dual effects on the compressibility of shale, namely, a certain amount of carbonate minerals can increase brittleness, and excessive carbonate minerals cause strength increase and fracture toughness increase, so that the improvement is not facilitated, which is consistent with the fact that carbonate rocks are used as fracturing barrier layers and natural fractures are stopped in carbonate rock layers in the actual fracturing process; the traditional shale brittleness index calculation method based on mineral composition cannot reflect the dual function of carbonate minerals on shale compressibility.

The plasticity of the organic matter has an influence on the brittleness of the shale, for example, when the diagenesis strength is weak, the content of the organic matter is increased, the static Young modulus and Poisson ratio of the shale are reduced, and the brittleness is weakened, so that the compressibility of the shale rich in the organic matter is determined to be poor.

Therefore, how to better embody the dual functions of carbonate minerals on the compressibility of shale and consider the influence of organic matters on the brittleness of shale, the improvement of the accuracy of the obtained brittleness index of shale becomes a problem to be solved urgently.

Disclosure of Invention

The invention aims to reflect the dual functions of carbonate minerals on the compressibility of the shale and improve the accuracy of the brittleness index of the shale; an improved shale brittleness index determination method based on mineral composition is provided; the method solves the problems that the dual functions of carbonate minerals on the compressibility of the shale cannot be reflected and the influence of organic matter plasticity on the brittleness of the shale is not considered.

In order to solve the technical problem, an embodiment of the present invention provides an improved shale brittleness index determination method based on mineral composition, including:

s11 identifying the type of the cheese in the shale to be detected through a kerogen scope; the kerogen types are I type, II type and III type;

s12 determination of total organic carbon content W in shale by organic carbon analysis_o；

S13, determining a conversion coefficient K according to the type of the kerogen and the evolution stage, and determining the total organic carbon content W according to the total organic carbon content_oThe conversion coefficient K and the organic matter density rho_oAnd rock density ρ_mCalculating the organic matter volume fraction V_oAnd converted into organic matter volume content V_organic；

S14 determination of content W of long-grained quartz minerals in shale by X-ray diffraction whole-rock mineral analysis_flesicCarbonate mineral content W_carbonateClay mineral content W_clayAnd the sum of the inorganic mineral contents V_im；

S15, according to the organic matter volume content V_organicThe sum of the mineral contents of the inorganic substances V_imSaid carbonate mineral content W_carbonateThe long-grained quartz mineral content W_flesicAnd the clay mineral content W_clayCarrying out normalization treatment to obtain the volume content V of carbonate minerals_carbonateVolume content of long-grained and long-grained minerals V_flesicAnd clay mineral volume content V_clay；

S16, according to the organic matter volume content V_organicThe volume content V of carbonate mineral_carbonateThe volume content V of the long-grained quartz minerals_flesicAnd said clay mineral objectVolume content V_clayObtaining shale brittleness index B based on mineral composition_rit。

In one embodiment, the step S12 includes: removing inorganic carbon from the shale sample to be tested by using dilute hydrochloric acid, and converting the organic carbon into CO by combustion oxidation in high-temperature oxygen flow₂Detection of CO using a detector₂The total organic carbon content W is calculated_o。

In one embodiment, the step S13 includes: volume fraction of organic matter V_oThe formula of (1) is:

V_o＝W_o×K×ρ_m/ρ_o； (4)

wherein, V_oIs the organic matter volume fraction; w_oIs the total organic carbon content; k is an organic matter conversion coefficient; rho_mThe shale density is 2.5g/cm³；ρ_oThe organic matter density is 1.0g/cm³；

From V_organic＝V_o×V_mCalculating the volume content V of organic matter_organic。V_mIs the entire shale sample volume, considered as 1.

In one embodiment, the transformation coefficients K for different types of kerogen differ in value at different evolution stages;

the value of the type I kerogen in the diagenesis stage is 1.25, and the value of the type I kerogen in the final stage of the deep diagenesis stage is 1.2;

the value of the type II kerogen is 1.34 in the diagenesis stage and 1.19 in the final stage of the deep diagenesis stage;

the value of the type III kerogen in the diagenesis stage is 1.48, and the value of the type III kerogen in the late stage of the deep diagenesis stage is 1.18.

In one embodiment, the step S14 includes: grinding the shale sample to be detected into 200-mesh powder, placing the powder in a sample chamber of an X-ray diffraction instrument for X-ray scanning and mineral analysis to respectively obtain the content W of carbonate minerals_carbonateLong-grained and long-grained minerals content W_flesicClay mineral content W_clayAnd the sum of the inorganic mineral contents V_im。

In one embodiment, the step S15 includes:

volume content of long-grained and British minerals V_flesic＝W_flesic/V_im×(V_m-V_organic)；

Volume content of carbonate mineral is V_carbonate＝W_carbonate/V_im×(V_m-V_organic)；

Clay mineral volume content of V_clay＝W_clay/V_im×(V_m-V_organic)。

In one embodiment, the step S16 includes: the formula of the shale brittleness index is as follows:

B_rit＝(V_flesic+V_carbonate)/(V_clay+V_flesic+V_carbonate+V_organic)； (5)

the value obtained in S15 and the organic matter volume content V in S13_organicSubstituting into a formula to obtain a shale brittleness index B_rit。

The method has the advantages that the method improves the calculation method of the shale brittleness index based on the mineral composition according to the mechanical property of the carbonate mineral and by considering the plastic influence of organic matters, can reflect the dual functions of the carbonate mineral on the shale compressibility, and improves the accuracy of the shale brittleness index by considering the influence of the matrix on the rock brittleness.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

The technical solution of the present invention is further described in detail by the accompanying drawings and embodiments.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:

FIG. 1 is a flow chart of an improved method for determining shale brittleness index based on mineral composition according to an embodiment of the present invention;

fig. 2 is a schematic diagram of an improved shale brittleness index determination method based on mineral composition and analysis of shale brittleness index correlation based on rock mechanical parameters according to an embodiment of the present invention.

Detailed Description

Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

The embodiment of the invention provides an improved shale brittleness index determination method based on mineral composition, which is shown in a reference figure 1 and comprises the following steps:

s11, identifying the type of the cheese root in the shale to be detected through a kerogen scope; the kerogen types are I type, II type and III type;

s12 determination of total organic carbon content W in shale by organic carbon analysis_o；

S13, determining a conversion coefficient K according to the type of kerogen and the evolution stage, and determining the conversion coefficient K according to the total organic carbon content W_oConversion coefficient K, organic matter density rho_oAnd rock density ρ_mCalculating the organic matter volume fraction V_oAnd converted into organic matter volume content V_organic(ii) a S14 determination of content W of long-grained quartz minerals in shale by X-ray diffraction whole-rock mineral analysis_flesicCarbonate mineral content W_carbonateClay mineral content W_clayAnd the sum of the inorganic mineral contents V_im；

S15 based on organic matterVolume content V_organicThe sum of mineral contents of inorganic substances V_imMineral content of carbonate W_carbonateLong-grained and long-grained minerals content W_flesicAnd clay mineral content W_clayCarrying out normalization treatment to obtain the volume content V of carbonate minerals_carbonateVolume content of long-grained and long-grained minerals V_flesicAnd clay mineral volume content V_clay；

S16, according to the organic matter volume content V_organicCarbonate mineral volume content V_carbonateVolume content of long-grained and long-grained minerals V_flesicAnd clay mineral volume content V_clayObtaining shale brittleness index B based on mineral composition_rit。

In the embodiment, the calculation method of the shale brittleness index based on mineral composition is improved according to the mechanical property of the carbonate mineral and by considering the organic matter plasticity influence, the dual effects of the carbonate mineral on the shale compressibility can be reflected, the influence of the matrix on the rock brittleness is considered, and the precision of the shale brittleness index is improved.

The above steps will be described in detail below.

In the step S11, before the kerogen identification, kerogen separation is performed, and then the separated kerogen is placed under an optical microscope for kerogen component identification, and the routine identification components are classified as: the components of coal quality, wood quality, herbage, algae and amorphous form, and the type of kerogen is judged by mirror identification of component classification.

In step S12, the sample is treated with dilute hydrochloric acid to remove inorganic carbon, so that organic carbon is converted into CO by combustion and oxidation in high-temperature oxygen flow₂Detection of CO using a detector₂The total organic carbon content W is calculated_o。

In step S13, first, determining a corresponding transformation coefficient K according to the type of kerogen and the evolution stage of kerogen identified in step S11; calculating the organic matter volume fraction V_oThe formula of (1) is:

V_o＝W_o×K×ρ_m/ρ_o； (4)

wherein the conversion coefficient K is the organic carbon content converted into the organic matter content, and the shale density rho_mThe value is 2.5g/cm3, and the density of organic matters is rho_oTaking the value as 1.0g/cm3, and adding the total organic carbon content W obtained in the step S12_oConversion coefficient K corresponding to kerogen type of shale to be measured and shale density rho_mAnd organic matter density ρ_oSubstituting into a formula to obtain the volume fraction Vo of the organic matter, and then adding the volume fraction V of the organic matter_oAnd the entire shale sample volume V_m(V_m1), the formula V is substituted into_organic＝V_o×V_mCalculating the volume content V of organic matter_organic。

In this embodiment, the conversion coefficients K of different types of kerogen at different evolution stages are different, and are between 1.1 and 1.5, which are determined according to the organic matter type in shale and the diagenetic evolution stage, and the corresponding relationship is as follows:

the value of the type I kerogen is 1.25 in the diagenesis stage and 1.2 in the final stage of the deep diagenesis stage;

the value of the type II kerogen is 1.35 in the diagenesis stage and 1.19 in the late stage of the deep diagenesis stage;

the value of the type III kerogen is 1.48 in the diagenesis stage and 1.18 in the late stage of the deep diagenesis stage.

As shown in table 1.

TABLE 1 organic matter conversion factor Ktable (according to Tissot and Welte,1978)

In the step S14, the shale sample to be tested is ground into 200 mesh powder, and the powder is placed in a sample chamber of an X-ray diffraction instrument for X-ray scanning and mineral analysis to obtain the carbonate mineral content W_carbonateLong-grained and long-grained minerals content W_flesicClay mineral content W_clayAnd the sum of the inorganic mineral contents V_im。

Among them, the principle of X-ray diffraction quantitative analysis: the task of quantitative analysis of phases is to determine the content of each phase in a heterogeneous material by accurately measuring the diffraction intensity of each phase in a mixture using X-ray diffraction techniques. The theoretical basis is that the volume or weight of a substance participating in diffraction is directly proportional to the intensity of the diffraction produced. Therefore, the volume fraction or the weight fraction of a phase in the mixture, which is related to diffraction, can be determined by the magnitude of the diffraction intensity, and the content of the phase in the mixture can be determined.

In step S15, the volume content V of the long and british minerals is obtained by normalization processing_flesic＝W_flesic/V_im×(V_m-V_organic) (ii) a Volume content of carbonate mineral is V_carbonate＝W_carbonate/V_im×(V_m-V_organic) (ii) a Clay mineral volume content of V_clay＝W_clay/V_im×(V_m-V_organic)。

In the above step S16, the organic matter volume content V is obtained in the steps S13 and S15_organicVolume content of long-grained and long-grained minerals V_flesicA carbonate mineral volume content of V_carbonateClay mineral volume content V_claySubstituting formula (5)

B_rit＝(V_flesic+V_carbonate)/(V_clay+V_flesic+V_carbonate+V_organic) (5)

And obtaining the shale brittleness index.

The technical scheme of the invention is explained in detail by the following specific embodiments, and the correctness of the scheme is verified:

taking second-stage shale of a Hongkong oilfield hole as an example, calculating according to the above steps to obtain 17 shale samples, which are respectively marked as A1-A17, and the specific calculation process is specifically illustrated by taking sample A1 as an example.

In the first step, the results of the observation by a kerogen mirror show that the A1 sample is type I kerogen, and the conversion coefficient K is determined according to the type of the kerogen.

Secondly, determining the total organic carbon content W in the shale through organic carbon analysis_oWill stand byThe sample is treated by removing inorganic carbon with dilute hydrochloric acid, burning and oxidizing in high-temperature oxygen flow, and converting organic carbon into CO₂Then detecting CO by a detector₂To calculate the total organic carbon content, the organic carbon determinator determines that the total organic carbon content of the sample A1 is W_o＝5.471％。

Thirdly, after the shale A1 is determined to be in the diagenetic stage, taking the conversion coefficient K as 1.25 by referring to the organic matter conversion coefficient table 1, and calculating the organic matter volume fraction V in A1 by using the organic matter volume fraction formula (4)_o＝W_o×K×ρ_m/ρ_oThe total shale sample volume was considered as V, 5.471% × 1.25 × 2.5/1.0 ═ 17.100%_m1, obtaining the organic matter volume content V_organic＝V_o×V_m＝17.100％×1＝17.100％。

And fourthly, determining the volume fraction of inorganic minerals in the shale through X-ray diffraction whole-rock mineral analysis. Grinding the sample to be detected into powder of 200 meshes, and placing the powder in a sample chamber of an X-ray diffraction instrument for X-ray diffraction scanning and mineral analysis. The X-ray diffraction whole rock mineral analysis result shows that the content W of long-quartz minerals in A1_flesic47, carbonate mineral content W_carbonate26, clay mineral content W_clay20, the sum of the contents of various inorganic minerals is V_im＝100；

Fifthly, after normalization, the volume content V of the long-grained and quartzitic minerals is obtained_flesic＝W_flesic/V_im×(V_m-V_organic) 38.963% in 47/100 × (1-17.100%), carbonate mineral content V_carbonate＝W_carbonate/V_im×(V_m-V_organic) 26/100 x (1-17.100%) -21.554%, clay mineral volume content V_clay＝W_clay/V_im×(V_m-V_organic)＝16.580％。

And sixthly, obtaining the shale brittleness index based on mineral composition according to the formula (5):

B_rit＝(V_flesic+V_carbonate)/(V_clay+V_flesic+V_carbonate+V_organic) = (38.963% + 21.554%)/(16.580% + 38.963% + 21.554% + 17.100%) -0.642; the improved mineral composition based shale friability index in each of the a2 to a17 samples can be calculated sequentially according to the above procedure.

Further, the correctness of the improved shale brittleness index determination method based on mineral composition provided by the embodiment of the invention can be verified:

the shale brittleness index based on rock mechanical parameters is the most accurate method for evaluating the shale brittleness at present, and the calculation method is to obtain the Young modulus and the Poisson ratio of the shale through a rock triaxial mechanical test, further normalize the Young modulus and the Poisson ratio, and carry out weighted summation according to a weight of 0.5.

The Young modulus and Poisson ratio of each shale sample are obtained through rock triaxial mechanical test and are respectively recorded as E₁To E₁₇And mu₁To mu₁₇Find the corresponding maximum value E_max＝MAX{E₁,E₂,…,E₁₇}、E_min＝MIN{E₁,E₂,…，E₁₇}、μ_max＝MAX{μ₁,μ₂,…,μ₁₇}、μ_min＝MIN{μ₁,μ₂,…，μ₁₇Thus obtaining each sample E_Rriti＝(E_i-E_min)/(E_max-E_min) X 100 and μ_Rriti＝(μ_max-μ_i)/(μ_max-μ_min) X 100, from the formula B_riti＝(E_Rriti+μ_Rriti) Obtaining a shale brittleness index, wherein i represents a sample marker, i ═ 1,2, …, 17;

e is the Young's modulus, E_RritiFor normalized Young's modulus, μ is Poisson's ratio, μ_RritiAs normalized Poisson's ratio, B_ritiIs a brittleness index.

The improved shale brittleness index based on the mineral composition and the shale brittleness index based on the rock mechanical parameters obtained through the steps are subjected to correlation analysis, the shale brittleness index based on the mineral composition and the shale brittleness index based on the rock mechanical parameters have a good linear positive correlation relationship as shown in figure 2, and therefore the correctness of the improved shale brittleness index determination method based on the mineral composition can be used for evaluating the shale brittleness.

The invention provides an improved shale brittleness index determination method based on mineral composition, which improves a calculation method of the shale brittleness index based on mineral composition according to the mechanical property of carbonate minerals and considering organic matter plasticity influence, can reflect the dual functions of the carbonate minerals on the shale compressibility, considers the influence of a matrix on the rock brittleness, and improves the accuracy of the shale brittleness index.

It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.