Method for measuring shale porosity by using rock density and fluid mass difference

Abstract

The invention relates to the field of geological exploration, and discloses a method for measuring shale porosity by using rock density and fluid mass difference, which comprises the following steps: firstly, measuring the mass and apparent volume of a blocky rock sample, calculating the apparent density of the blocky rock sample, then crushing, extracting and drying the rock sample, metering the fluid mass loss, and measuring the skeleton density of the dry powder sample. And finally, estimating the volume difference corresponding to the unit mass rock by using the reciprocal difference of the rock apparent density and the skeleton density, and calculating the total porosity of the rock sample through fluid loss mass correction. The porosity is calculated according to the density and fluid mass difference of the rock samples with different particle sizes, the method is not restricted by the sizes of the rock samples and fluid contained in the rock samples, the closed pores in the rock can be measured, correction is carried out by utilizing the fluid loss mass in the crushing, oil washing / extraction and drying treatment processes, and the more accurate shale total porosity can be obtained.

Description

Technical Field

[0001] The invention relates to the field of geological exploration, and in particular to a method for measuring shale porosity by utilizing differences in rock density and fluid quality. Background Art

[0002] Rock pores are the storage spaces for hydrocarbon-containing fluids, which can be divided into open pores and closed pores. There are many methods for measuring rock pore volume at present, and the commonly used ones are mercury injection method, helium porosimetry, gas adsorption method, nuclear magnetic resonance method, small-angle neutron scattering method, small-angle X-ray scattering method, etc. Among them, the porosity measurement method using fluids such as mercury, helium and nitrogen to inject into rocks can only measure the open pore volume in the rock sample, while the ray detection method using nuclear magnetic pulse, neutron beam or X-ray cannot obtain the vacancy signal of the fluid that has escaped from the rock during the drilling sampling process. In addition, the porosity measurement method that combines fluid injection with ray detection, such as saturated fluid small-angle scattering method and saturated fluid nuclear magnetic resonance method, is also difficult to fully inject fluid into dense shale samples, especially nanoscale open pores and closed pores.

[0003] Unlike conventional sandstone, organic-rich shales mainly develop nano-scale pores, extremely complex pore structures, and a large number of closed pores. The determination of these closed pores is a prerequisite for accurately obtaining the total porosity of shale. The shale porosity GRI test method developed by the Gas Research Institute is to crush the rock sample to a minimum of 200 mesh to open the closed pores in the shale to the greatest extent. It is worth noting that the apparent volume of the crushed sample in the GRI method cannot be directly measured, but is first calculated by assuming that the density of the rock plunger and the powder sample is consistent, and then using the mass ratio of the plunger to the powder sample. However, in the process of rock crushing, its closed pores will be gradually opened, and the density of the corresponding rock sample will gradually increase, which will lead to a serious deviation in the total volume calculation result of the powder sample by the GIR method. Summary of the invention

[0004] The purpose of the present invention is to propose a method for measuring shale porosity by using the difference between rock density and fluid mass, so as to solve the technical problem that the existing method for measuring shale porosity by using the difference between rock density and fluid mass is not accurate.

[0005] Specifically, the present invention provides a method for measuring shale porosity by using the difference between rock density and fluid mass, comprising the following steps:

[0006] S1. Obtain the mass m of the block rock sample to be tested i ;

[0007] S2. Measure the apparent volume v of the rock sample i ;

[0008] S3. Calculate the apparent density ρ based on the mass and apparent volume of the rock sample i ;

[0009] S4, performing drying pretreatment on the rock sample to obtain a pretreated rock sample;

[0010] S5. Measure the mass m of the pre-treated rock sample d1 ;

[0011] S6. Calculate the fluid loss per unit mass of the block rock m based on the mass of the rock sample and the mass of the pre-treated rock sample. f1 ;

[0012] S7. After the pre-treated rock sample is crushed to a preset mesh size, the crushed mass is taken as m d2 The extraction experiment was carried out, and the rock samples were further dried after extraction to obtain the rock samples after crushing and extraction. Then, according to the mass m of the rock samples after crushing, d2 , the mass of the rock sample after crushing and extraction m d3 , calculate the fluid loss per unit mass of powdered rock m f2 ;

[0013] S8. Weigh a certain mass of the dry powder sample in step S7 and measure its helium density ρ d ;

[0014] S9, according to the helium density ρ d , apparent density ρ i , fluid loss per unit mass of massive rock m f1 , fluid loss per unit mass of powdered rock m f2 Calculate the total porosity of the rock sample.

[0015] The beneficial effects provided by the present invention are: the porosity is calculated by the difference in density and fluid mass of rock samples with different particle sizes, which is not restricted by the size of the rock sample and the fluid it contains, and can measure the closed pores in the rock. At the same time, the fluid loss mass in the process of crushing, oil washing / extraction and drying is used for correction, so that a more accurate total shale porosity can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic flow chart of the method of the present invention;

[0017] Figure 2 This is a schematic diagram comparing the measured porosity and the logged porosity of Well XY10. DETAILED DESCRIPTION

[0018] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0019] Before formally describing the present invention, the scheme of the present invention is first generally described for easy understanding.

[0020] Please refer to Figure 1 The present invention provides a method for measuring shale porosity by using rock density and fluid mass difference, comprising the following steps:

[0021] S1. Obtain the mass m of the block rock sample to be tested i ;

[0022] S2. Measure the apparent volume v of the rock sample i ;

[0023] It should be noted that the method for measuring the apparent volume of the rock sample in step S2 includes: a contact measurement method and a non-contact measurement method.

[0024] The contact measurement method in the present invention can adopt the particle tapping method, mercury injection method, drainage quality difference method, etc., and the non-contact measurement method can adopt the direct measurement method, laser three-dimensional volume scanning method, etc. In addition, if the contact apparent volume measurement method is adopted, in order to avoid the error caused by the contact measurement, another parallel sample with a mass similar to that of the rock sample can be taken for measurement.

[0025] S3. Calculate the apparent density ρ based on the mass and apparent volume of the rock sample i ;

[0026] It is easy to understand that the apparent density ρ in the present invention is i The calculation formula is as follows:

[0027] S4, performing drying pretreatment on the rock sample to obtain a pretreated rock sample;

[0028] It should be noted that before the drying pretreatment in step S4, oil washing treatment is also performed according to the maturity of the rock sample. If it is a high-maturity rock sample, oil washing treatment is not performed, otherwise oil washing treatment is required; wherein the high-maturity rock sample specifically refers to: the corresponding maturity index exceeds the equivalent vitrinite reflectance 1.3%Ro.

[0029] It should be noted that there are many methods for measuring the maturity of shale, such as rock pyrolysis analysis, vitrinite reflectance, and other geochemical indicators. Any of these methods can be used for measurement and judgment in the present invention.

[0030] As an embodiment, taking the vitrinite reflectance as an example, the principle is that the reflectance of vitrinite (organic matter formed by plant remains) increases with the increase of temperature, which directly reflects the degree of thermal evolution.

[0031] The judgment method is mainly as follows: Ro<0.5% immature biogas stage; 0.5%≤Ro≤1.3% medium maturity oil window stage; Ro>1.3%: high maturity gas stage. Of course, other indicators can also be used to judge the maturity, and the present invention is not limited to this.

[0032] In addition, the temperature of the drying pretreatment in step S4 of the present invention is not less than 110° C., and the drying time is based on the time when the mass of the rock sample is reduced to a constant value.

[0033] S5. Measure the mass m of the pre-treated rock sample d1 ;

[0034] It should be noted that the weighing process needs to prevent the sample from being exposed to air for a long time, because after contact with air, the sample will absorb water and cause quality deviation.

[0035] S6. Calculate the fluid loss per unit mass of the block rock m based on the mass of the rock sample and the mass of the pre-treated rock sample. f1 ;

[0036] In step S6 of the present invention, the fluid loss per unit mass of the block rock m f1 The calculation formula is as follows:

[0037] S7. After the pre-treated rock sample is crushed to a preset mesh size, the crushed mass is taken as m d2 The extraction experiment was carried out, and the rock samples were further dried after extraction to obtain the rock samples after crushing and extraction. Then, according to the mass m of the rock samples after crushing, d2 , the mass of the rock sample after crushing and extraction m d3 , calculate the fluid loss per unit mass of powdered rock m f2 ;

[0038] It should be noted that in the present invention, the rock sample is crushed to a particle size of less than 200 mesh, and then a Soxhlet extraction experiment is carried out on it. The extraction solvent is recommended to use a ternary solvent of chloroform-methanol-acetone. After the extraction experiment, the solvent needs to be fully evaporated by a relatively high drying temperature and time.

[0039] It is easy to understand that the fluid loss per unit mass of the powdered rock in step S7 of the present invention is m f2 The calculation formula is as follows:

[0040] It should be noted that the step S7 and the step S4 can also be combined to obtain the total fluid loss m of the rock sample. f (i.e. m fl and m f2The sum of the above), that is, the rock sample is weighed once after the rock sample is subjected to oil washing, drying pretreatment, crushing, Soxhlet extraction and drying treatment in sequence.

[0041] S8, weigh a certain mass of the dry powder sample in step S7, and measure its helium density ρ d ;

[0042] It should be noted that considering the possible influence of air adsorption by the powder during the drying process in the oven, it is recommended to discard the initial test data of helium density. This step also needs to ensure a certain saturation pressure and equilibrium time to allow the helium molecules to be fully filled, and to carry out leakage pressure correction for the corresponding equilibrium time.

[0043] S9, according to the helium density ρ d , apparent density ρ i , fluid loss per unit mass of massive rock m f1 , fluid loss per unit mass of powdered rock m f2 Find the total porosity of the rock sample.

[0044] The calculation formula of the total porosity of the rock sample in step S9 of the present invention is as follows:

[0045] The present invention is explained by taking measured data as an example.

[0046] First, determine the mass of the block rock sample to be tested at a depth of 2554m in Well XY10 (m i =8.7316g), and at the same time, a parallel sample (m i` =8.1929 g). Measure the apparent volume (v) of the parallel samples. i` =3.0566cm 3 ), calculate the apparent density of the parallel block sample equivalent to the original rock sample Then the original block rock sample was pre-treated by oil washing and drying, and the mass of the pre-treated rock sample (m d1 =8.6943g), calculate the fluid mass loss per unit mass of rock during the pretreatment process The pre-treated rock samples were further crushed into powder with a particle size of 200-400 mesh and subjected to extraction and drying treatment. The fluid loss per unit rock mass (m f2 =0.0002 g / g), weigh a certain mass of dry powder sample and measure its helium density (ρ d =2.7239g / cm 3 ), and finally use the formula The total porosity of the shale sample at a depth of 2554m in Well XY10 can be obtained.

[0047] By comparing the changing trends of the measured porosity and the well logging porosity in the Lianggaoshan Formation and Dongyuemiao Section of Well XY10, it can be seen that the two have good consistency ( Figure 2 ).

[0048] The beneficial effects of the present invention are as follows: porosity is calculated by the difference in density and fluid mass of rock samples with different particle sizes, which is not restricted by the size of the rock sample and the fluid it contains, and can measure the closed pores in the rock. At the same time, the fluid loss mass in the process of crushing, oil washing / extraction and drying is used for correction, so that a more accurate total shale porosity can be obtained.

[0049] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for measuring shale porosity using the difference between rock density and fluid mass, characterized in that: The following steps are involved: S1. Obtain the mass m of the block rock sample to be tested i ; S2. Measure the apparent volume v of the rock sample i ; S3. Calculate the apparent density ρ based on the mass and apparent volume of the rock sample i ; S4, performing drying pretreatment on the rock sample to obtain a pretreated rock sample; S5. Measure the mass m of the pre-treated rock sample d1 ; S6. Calculate the fluid loss per unit mass of the block rock m based on the mass of the rock sample and the mass of the pre-treated rock sample. f1 ; S7. After the pre-treated rock sample is crushed to a preset mesh size, the crushed mass is taken as m d2 The extraction experiment was carried out, and the rock samples were further dried after extraction to obtain the rock samples after crushing and extraction. Then, according to the mass m of the rock samples after crushing, d2 , the mass of the rock sample after crushing and extraction m d3 , calculate the fluid loss per unit mass of powdered rock m f2 ; S8. Weigh a certain mass of the dry powder sample in step S7 and measure its helium density ρ d ; S9, according to the helium density ρ d , apparent density ρ i , fluid loss per unit mass of massive rock m f1 , fluid loss per unit mass of powdered rock m f2 Find the total porosity of the rock sample.

2. A method for measuring shale porosity using rock density and fluid mass differences as claimed in claim 1, characterized in that: The method for measuring the apparent volume of the rock sample in step S2 includes: a contact measurement method and a non-contact measurement method.

3. A method for measuring shale porosity using rock density and fluid mass differences as claimed in claim 2, characterized in that: When the contact measurement method is used to measure the apparent volume, a parallel sample with a mass similar to that of the rock sample must be taken for measurement.

4. The method for measuring shale porosity by using the difference between rock density and fluid mass as claimed in claim 1, characterized in that: Before the drying pretreatment in step S4, oil washing treatment is also performed according to the maturity of the rock sample. If the rock sample has a high maturity, oil washing treatment is not performed, otherwise oil washing treatment is required; wherein the high maturity rock sample specifically refers to: the corresponding maturity index exceeds the equivalent vitrinite reflectance 1.3%Ro.

5. The method for measuring shale porosity by using the difference between rock density and fluid mass as claimed in claim 1, characterized in that: The temperature of the drying pretreatment in step S4 is not less than 110° C., and the drying time is based on the time when the mass of the rock sample is reduced to a constant value.

6. The method for measuring shale porosity by using the difference between rock density and fluid mass as claimed in claim 1, characterized in that: In step S6, the fluid loss per unit mass of the block rock m f1 The calculation formula is as follows:

7. The method for measuring shale porosity by using the difference between rock density and fluid mass as claimed in claim 1, characterized in that: The fluid loss per unit mass of powdered rock in step S7 is m f2 The calculation formula is as follows:

8. The method for measuring shale porosity by using the difference between rock density and fluid mass as claimed in claim 1, characterized in that: The calculation formula for the total porosity of the rock sample in step S9 is as follows:

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