CN111239372B - Carbonate rock pore structure classification method based on overburden seepage experiment - Google Patents
Carbonate rock pore structure classification method based on overburden seepage experiment Download PDFInfo
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
- G01N15/08—Investigating permeability, pore-volume, or surface area of porous materials
- G01N15/082—Investigating permeability by forcing a fluid through a sample
- G01N15/0826—Investigating permeability by forcing a fluid through a sample and measuring fluid flow rate, i.e. permeation rate or pressure change
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
- G01N15/08—Investigating permeability, pore-volume, or surface area of porous materials
- G01N15/088—Investigating volume, surface area, size or distribution of pores; Porosimetry
Abstract
The invention relates to the field of reservoir rock pore structure classification in the oil and gas field development process, in particular to a carbonate rock pore structure classification method based on an overburden pressure seepage experiment, which comprises the following steps: preparing a rock sample, and measuring the gas permeability of the rock sample; after the rock sample is saturated with the simulated oil, performing a permeability-confining pressure relation determination experiment to obtain a permeability-confining pressure curve; performing sectional fitting on the permeability-confining pressure curve to obtain a permeability-confining pressure fitting curve, and analyzing the parameter change rate of the sectional fitting; observing the rock core, and primarily judging the pore structure type according to the rock core observation result; according to the difference of the fitting parameter change rates of different sections and by combining the core observation result and the theoretical analysis of the permeability-confining pressure fitting curve characteristics, the pore structure types of the core are divided, and the pore structure classification result of the classification method provided by the invention is closer to the actual situation of the carbonate reservoir.
Description
Technical Field
The invention relates to the field of reservoir rock pore structure classification in the oil and gas field development process, in particular to a carbonate rock pore structure classification method based on an overburden vadose experiment.
Background
The characterization and classification methods of the rock pore structure are many, for example, mercury intrusion, cast body slices, nuclear magnetic resonance and other means can be used for rock pore structure research and classification, but the classification of the rock pore structure by adopting the methods is only a static analysis and evaluation result, and does not reflect the pore structure and the dynamic change characteristics thereof under the actual formation conditions, particularly carbonate reservoir, crack development and high pressure generally, in the development process, the oil layer pressure is attenuated quickly, the rock pore structure is changed continuously, and the pore structure type is divided by adopting a dynamic evaluation means.
Disclosure of Invention
The embodiment of the invention provides a carbonate rock pore structure classification method based on an overburden seepage experiment, which can solve the problems in the prior art.
The invention provides a carbonate rock pore structure classification method based on an overburden seepage experiment, which comprises the following steps:
preparing a rock sample, and measuring the gas permeability of the rock sample;
after the rock sample is saturated with the simulated oil, performing a permeability-confining pressure relation determination experiment to obtain a permeability-confining pressure curve;
performing sectional fitting on the permeability-confining pressure curve to obtain a permeability-confining pressure fitting curve, and analyzing the parameter change rate of the sectional fitting;
observing the rock core, and primarily judging the pore structure type according to the rock core observation result;
and dividing the pore structure type of the rock core according to the difference of the fitting parameter change rates of different sections and by combining the rock core observation result and the theoretical analysis of the permeability-confining pressure fitting curve characteristics.
Preferably, the piecewise fitting method of the permeability-confining pressure curve comprises the following steps:
dividing a permeability-confining pressure curve into a high-pressure section and a low-pressure section, and respectively fitting data of the high-pressure section and the low-pressure section by adopting the following formula (1):
K＝aP-b (1)
in the formula, K is the oil phase permeability under a certain confining pressure, P is the confining pressure, and a and b are fitting parameters.
Preferably, the method of fitting the parameter change rate analysis is:
calculating the change rate delta a and delta b of the fitting parameters from the low-pressure section to the high-pressure section by adopting the formula (2) and the formula (3):
in the formula, Δ a and Δ b are the rates of change of the fitting parameters from the low-pressure stage to the high-pressure stage, respectively, and a1, a2, b1 and b2 are the fitting parameters for the low-pressure stage and the high-pressure stage, respectively.
Preferably, the core observation method comprises the following steps:
observing the appearance of the rock core, slicing the rock core, observing the size of pores, mineral composition and micro-crack distribution of the sliced rock core under an electron microscope, and then primarily judging the type of the pore structure.
Preferably, the result of the division of the pore structure type is:
according to core observation, the core pore structure types are divided into a crack type and a matrix pore type, and the crack type pore structure is divided into a crack micropore and a crack dissolving pore;
when the delta a is more than 50 percent, the pore structure is in a crack type, and when the delta a is less than 50 percent, the pore structure is in a matrix pore type; when the delta b is more than 50% and less than 70%, the pore structure is a crack-soluble pore type; when the delta b is more than 70 percent, the pore structure is of a crack micropore type.
Compared with the prior art, the invention has the advantages that:
according to the method, under the condition of simulating an actual stratum, the seepage characteristics of the carbonate rock core under different confining pressure conditions are tested to obtain a permeability-confining pressure curve, the permeability-confining pressure curve is subjected to sectional fitting to obtain fitting parameters, the variation rate difference of the fitting parameters is analyzed, and the type of the rock pore structure is divided by combining related theoretical analysis and rock core observation, so that the obtained pore structure classification result is closer to the real condition of the carbonate rock reservoir.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a flow chart of a method of classification of a pore structure of rock according to the invention;
FIG. 2 is a schematic structural view of an experimental apparatus for measuring a relationship between permeability and confining pressure according to the present invention
FIG. 3 is a graph of a piecewise fit of permeability versus confining pressure for different cores of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1, the invention provides a carbonate rock pore structure classification method based on an overburden seepage experiment, which comprises the following steps:
preparation of experimental materials and equipment:
firstly, experimental materials comprise a rock sample and a fluid, wherein the experimental rock sample is taken from an actual carbonate rock stratum, the natural rock sample is taken out, sealed by paraffin and sent to a laboratory, the rock sample is numbered after drilling and cutting, then the rock sample is washed by a mixture of ethanol and benzene, the rock sample can be cleaned after 5-7 days generally, then the rock sample is taken out and put into a drying box for drying, the moisture in the rock sample is removed, the temperature is set to be 80 ℃, about 10 hours generally is needed, and then the gas permeability of the rock sample is measured by a soap foam flow meter method. The experimental fluid adopts kerosene and simulated oil, the kerosene is mainly used for a constant flow pump and an intermediate container, and the density of the kerosene is 0.785g/cm3The viscosity was 1.558 mPa.s. The simulated oil is mainly used as a core seepage medium and prepared by blending crude oil, normal sunflower alkane and kerosene, and has the viscosity and the density of 0.9402mPa.s and 0.741g/cm respectively3。
The experimental equipment mainly comprises a constant temperature box, a piston type intermediate container, a pressure gauge, a high-pressure constant flow pump, a high-temperature high-pressure core holder, an annular pressure tracking pump, a flowmeter, an electronic balance and a vacuum pump, wherein the pressure range of the high-pressure constant flow pump is 0-65MPa, and the flow range is 0.00001-50 mL/min. The temperature resistance of the high-temperature and high-pressure rock core holder is 100 ℃ at most, the pressure resistance of the high-temperature and high-pressure rock core holder is 100MPa at most, and the highest temperature of the constant temperature box can reach 120 ℃. The equipment connection mode is as shown in figure 2, the high-pressure constant-flow pump outlet is connected with the inlet of the piston type intermediate container, the outlet of the piston type intermediate container is connected with the pressure gauge, the pressure gauge is simultaneously connected with the inlet of the core holder, the ring pressure tracking pump is further connected to the holder, the outlet of the holder is a flowmeter, and the instruments and the equipment are all arranged in the thermostat.
Determination of permeability-confining pressure relation curve:
firstly, weighing the mass of a rock core by using an electronic balance, recording as m1, then extracting air in a rock core hole by using a vacuum pump until the inside of the rock core hole reaches a vacuum state, filling simulation oil into the rock core hole to ensure that the hole is completely saturated with the simulation oil, then soaking the rock core into a beaker filled with the simulation oil, then placing the beaker into a constant temperature box, setting the temperature of the constant temperature box to be the formation temperature of the depth of the rock core, and aging the rock core in the simulation oil for about 15 days.
Taking out the core from the beaker, weighing the core on an electronic balance, and recording the mass as m2, wherein the pore volume Vp is: (m2-m1)/0.741, from which the porosity of the core can be calculated, the porosity φ being: Vp/VL, wherein VL is the apparent volume of the core. Opening a piston type middle container, pressing a piston into the bottom, filling simulated oil into the piston type middle container, connecting an experimental pipeline according to the connection mode shown in figure 2, loading a rock core into a rock core holder, opening a ring pressure tracking pump, adding confining pressure to the rock core, opening a high-pressure constant flow pump, setting a proper displacement pressure, ensuring that the confining pressure is 2.5-3MPa higher than the displacement pressure, and displacing the rock core by adopting the simulated oil by at least more than 5PV (pore volume).
Measuring and recording outlet flow of the holder by adopting a flowmeter under the displacement pressure condition, keeping the displacement pressure unchanged, adjusting a ring pressure tracking pump to slowly raise confining pressure, namely slowly increasing effective stress, wherein the pressurization interval is generally 3-5MPa, keeping the pressure at each set confining pressure point for more than 30min, measuring and recording the flow, and the confining pressure is increased to 30MPa at most (can be adjusted according to the actual stratum covering pressure condition). And after the test is finished, immediately stopping the high-pressure constant flow pump, emptying the fluid in the experiment pipeline, reducing the pressure of the ring pressure tracking pump, namely the confining pressure, to 0, opening the core holder, taking out the core, putting the core into a beaker filled with simulated oil, turning off the pump, and finishing the experiment.
Fitting of experimental data:
firstly, calculating the oil phase permeability of the rock core under different confining pressure conditions according to the flow and the displacement pressure obtained by the experiment and by combining the size of the rock core and the viscosity data of the simulated oil according to the Darcy's law, and drawing a permeability-confining pressure curve in a coordinate system by taking the permeability as a vertical coordinate and the confining pressure as a horizontal coordinate.
Dividing a permeability-confining pressure curve into two parts, wherein one part is a high-pressure section (confining pressure is more than 10MPa) and the permeability of the high-pressure section changes slowly along with the confining pressure, the other part is a low-pressure section (confining pressure is less than 10MPa) and the permeability of the low-pressure section changes rapidly along with the confining pressure, the two sections are fitted by using exponential functions, and the data of the high-pressure section and the low-pressure section are respectively fitted by adopting the following fitting equation:
K＝aP-b (1)
in the formula, K is the oil phase permeability under a certain confining pressure, P is the confining pressure, and a and b are fitting parameters. And analyzing and comparing the difference of the fitting parameters of the low-pressure section and the high-pressure section.
Thirdly, further processing the fitting parameters of the high-pressure section and the low-pressure section, and calculating the change rate delta a and delta b of the fitting parameters from the low-pressure section to the high-pressure section by adopting the following formula:
in the formula, a1 and a2 are fitting parameters of a low pressure section and a high pressure section, respectively, and b1 and b2 are fitting parameters of a low pressure section and a high pressure section, respectively.
And (3) core observation:
when the core is observed, firstly, the appearance of the core is preliminarily observed, including crack development, lithology and the like, then, the appearance characteristics of the core are observed in detail under a microscope, finally, the section is cut under a scanning electron microscope to determine the pore size, mineral composition, micro crack distribution and the like of the core, the initial judgment on the pore structure type is carried out by combining the core observation, the pore structure type of the core can be divided into two types, namely a crack type and a matrix pore type, and the crack type pore structure is divided into two types, namely a crack micropore and a crack dissolution hole.
Example 1
As shown in fig. 3, a series of permeability-confining pressure curves are obtained by testing the oil phase permeability of a carbonate rock core in a certain area of a firewood basin under different confining pressure conditions, the permeability-confining pressure curves are plotted and divided into a high pressure section and a low pressure section, then the data of the high pressure section and the low pressure section are respectively fitted, the obtained fitting parameters are shown in table 1, and the fitting parameter change rates Δ a and Δ b of the low pressure section and the high pressure section are calculated according to the formula (2) and the formula (3).
TABLE 1
TABLE 2
As shown in table 1, the cores Δ a and Δ b of different pore structure types have large differences, and the pore structure types of the cores can be classified according to the different ranges of Δ a and Δ b.
Core observation shows that, in the major category, the carbonate rock core has two major pore structure types of cracks and matrix pores, and for the crack type pore structure, the carbonate rock core also has two types of crack micropores and crack dissolving pores. Theoretical analysis shows that fitting parameters of the fracture micropore type low-pressure section and the fracture micropore type high-pressure section are different greatly, fitting parameters of the pore matrix type low-pressure section and the fracture matrix type high-pressure section are different slightly, and the difference is centered for fracture pore-dissolving type. Firstly, the pore structure types of the rock core can be divided into two types according to the size of delta a, namely, a matrix pore type and a fracture type, the delta a & gt 50% is the fracture type, and the delta a & lt 50% is the matrix pore type. And further subdividing the crack type pore structure types according to the size of delta b, wherein the crack type pore structure types are crack solution pore types when delta b is less than 50% and less than 70%, and the crack type pore structure types are crack micro-pore types when delta b is more than 70%, and the final pore structure type division results are shown in table 2.
In conclusion, the testing method provided by the invention has the advantages that the seepage characteristics of the carbonate rock core under different confining pressure conditions are tested under the condition of simulating an actual stratum, the permeability-confining pressure relation data are obtained, the data are subjected to segmented fitting to obtain fitting parameters, the variation rate difference of the fitting parameters is analyzed, and the rock pore structure type is divided by combining related theoretical analysis and rock core observation, so that the obtained pore structure classification result is closer to the actual condition of the carbonate rock reservoir, the testing efficiency is high, the experimental method is simple, the operation is easy, and the popularization is worthy.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention.
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.
Claims (2)
1. A carbonate rock pore structure classification method based on an overburden seepage experiment is characterized by comprising the following steps:
preparing a rock sample, and measuring the gas permeability of the rock sample;
after the rock sample is saturated with the simulated oil, performing a permeability-confining pressure relation determination experiment to obtain a permeability-confining pressure curve;
performing sectional fitting on the permeability-confining pressure curve to obtain a permeability-confining pressure fitting curve, and analyzing the parameter change rate of the sectional fitting;
observing the rock core, and primarily judging the pore structure type according to the rock core observation result;
dividing the pore structure type of the rock core according to the difference of the fitting parameter change rates of different sections and by combining the rock core observation result and the theoretical analysis of the permeability-confining pressure fitting curve characteristic;
the sectional fitting method of the permeability-confining pressure curve comprises the following steps:
dividing a permeability-confining pressure curve into a high-pressure section and a low-pressure section, and respectively fitting data of the high-pressure section and the low-pressure section by adopting the following formula (1):
K＝aP-b (1)
in the formula, K is the oil phase permeability under a certain confining pressure, P is the confining pressure, and a and b are fitting parameters;
the method for analyzing the change rate of the fitting parameters comprises the following steps:
calculating the change rate delta a and delta b of the fitting parameters from the low-pressure section to the high-pressure section by adopting the formula (2) and the formula (3):
in the formula, delta a and delta b are respectively the change rate of the fitting parameters from the low-pressure section to the high-pressure section, and a1, a2, b1 and b2 are respectively the fitting parameters of the low-pressure section and the high-pressure section;
the conditions for dividing the pore structure types are as follows:
according to core observation, the core pore structure types are divided into a crack type and a matrix pore type, and the crack type pore structure is divided into a crack micropore and a crack dissolving pore;
when the delta a is more than 50 percent, the pore structure is in a crack type, and when the delta a is less than 50 percent, the pore structure is in a matrix pore type; when the delta b is more than 50% and less than 70%, the pore structure is a crack-soluble pore type; when the delta b is more than 70 percent, the pore structure is of a crack micropore type.
2. The method for carbonate rock pore structure classification based on the overburden seepage test as recited in claim 1, wherein the method for preliminarily judging the core pore structure type comprises the following steps:
observing the appearance of the rock core, slicing the rock core, observing the size of pores, mineral composition and micro-crack distribution of the sliced rock core under an electron microscope, and then primarily judging the type of the pore structure.
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