CN109425567A - A kind of characterizing method of the permeability based on carbonate reservoir - Google Patents

Abstract

A characterization method based on the permeability of carbonate reservoirs. By determining the pore size boundary of the pore throat radius that can be characterized by adsorption method and high-pressure mercury intrusion method, the pore structure and pore structure below the pore size boundary measured by adsorption method are determined. The pore structure above the pore size boundary measured by the high-pressure mercury intrusion method is spliced to obtain the pore structure characteristics of carbonate reservoirs, the mercury injection saturation per unit pressure and the permeability of different samples, and the relationship between the maximum unit pressure mercury injection saturation and the permeability of different samples is established. High-precision functional relationship between permeability. The invention can characterize the pore structure characteristics of the full aperture section, so that the later test results are more accurate. The maximum unit pressure of mercury injection saturation is used to accurately calculate the permeability of carbonate reservoirs, avoiding the need to carry out a large number of other core experiments. While ensuring the accuracy of the quantitative evaluation results of carbonate reservoir permeability, it provides a The invention is a simple and practical new method, which can effectively save costs and has strong economical practicability.

Description

A characterization method based on the permeability of carbonate reservoirs

technical field

The invention relates to a quantitative characterization method of reservoir permeability, in particular to a characterization method based on the permeability of carbonate rock reservoirs.

Background technique

In carbonate reservoirs, the complexity of the rock pore structure results in strong heterogeneity of the reservoir, so that there is no high-precision functional relationship between porosity and permeability. The micro-nano pore structure parameters of shale reservoirs are usually measured by adsorption method and high-pressure mercury intrusion method, but the main problems in the measurement are: the measurement range of different methods is different, and it is impossible for adsorption method and high-pressure mercury intrusion method to comprehensively measure. Characterization of pore structure characteristics of micro-nanopores in shale reservoirs. Therefore, it is not feasible to use the permeability calculation formula based on porosity to calculate the permeability of complex carbonate reservoirs. In addition, since both the empirical constants in the free-fluid model and the empirical constants in the average model are difficult to accurately determine, it is also difficult to accurately calculate the permeability of complex carbonate reservoirs. In order to accurately determine the permeability of carbonate reservoirs, it is necessary to establish a high-precision functional relationship between this parameter and permeability, so as to accurately determine the permeability of complex carbonate reservoirs.

SUMMARY OF THE INVENTION

Aiming at the above problems and deficiencies in the prior art, the present invention provides a method for characterizing the permeability of carbonate rock reservoirs, which can accurately determine the permeability of carbonate rock reservoirs.

To achieve the above object, the present invention adopts the following technical solutions: a method for characterizing the permeability of carbonate reservoirs, comprising the following steps:

1) By determining the pore size boundary of the pore throat radius that can be characterized by adsorption method and high pressure mercury porosimetry, the pore structure below the pore size boundary measured by adsorption method and the pore structure above the pore size boundary measured by high pressure mercury porosimetry are spliced. , to obtain the pore structure characteristics of carbonate reservoirs;

2) Perform mercury intrusion experiments on rock reservoir samples with different void structures to obtain the mercury saturation per unit pressure and the permeability of different samples;

3) By comparing the maximum unit pressure mercury saturation of each sample, a high-precision functional relationship between the maximum unit pressure mercury saturation and permeability is established;

4) Based on the high-precision functional relationship, a formula for calculating the permeability of carbonate reservoirs with the maximum unit pressure mercury saturation as the parameter is established.

The beneficial effect of the method for characterizing the permeability of carbonate rock reservoirs implemented by the present invention is: by determining the pore size boundary of the pore throat radius that can be characterized by both the adsorption method and the high-pressure mercury intrusion method, the pore size boundary of the pore throat radius that can be characterized by the adsorption method will be measured by the adsorption method. The pore structure below the pore size boundary and the pore structure above the pore size boundary measured by the high-pressure mercury intrusion method can be used to characterize the pore structure characteristics of the full pore size section, and the characterization results are more accurate. have a positive effect.

Detailed ways

The steps of the present invention are further described in detail below.

A characterization method based on the permeability of a carbonate reservoir, comprising the following steps:

1) By determining the pore size boundary of the pore throat radius that can be characterized by adsorption method and high pressure mercury porosimetry, the pore structure below the pore size boundary measured by adsorption method and the pore structure above the pore size boundary measured by high pressure mercury porosimetry are spliced. , to obtain the pore structure characteristics of carbonate reservoirs.

In the high-pressure mercury intrusion test in this step, the mercury is injected into the columnar sample of shale by means of four-sided mercury injection. Mathematical relationship between wet contact angle and injection pressure, the Washburn equation. For sandstone and carbonate reservoirs, the yield strength of rock is generally higher, and its yield is generally above 180Mpa, while the test pressure of conventional mercury intrusion tests is generally below 200Mpa, so it is generally impossible to produce When the pressure is higher than the yield strength of the rock pore wall, there is no "throat expansion" effect when mercury enters the pore throat. For organic-rich shale reservoirs, due to their low yield strength, generally below 100Mpa, and the yield strength of organic pores in shale reservoirs is lower, under low pressure, mercury is injected into large pore sizes Pores, because the pore wall strength in shale is greater than the injection pressure, it is impossible to produce "throat expansion". However, when the injection pressure increases, the injection pressure is greater than the yield strength of the shale pore wall, which may produce a "throat expansion" effect. If the yield strength of shale is 60Mpa, the corresponding pore throat radius is about 20nm, that is, for this For samples, when the injection pressure is greater than 60Mpa, the pore throats below 20nm will be "expanded", and mercury molecules will enter them.

Pore size analysis was performed on the same sample by adsorption method and high pressure mercury intrusion method. In the overlapping section of pore size (below 80 nm) tested by high pressure mercury porosimetry and adsorption method, it is obvious that the pore size tested by high pressure mercury porosimetry is larger than that measured by adsorption method, and the "throat expansion" effect of high pressure mercury porosimetry is obvious.

2) Perform mercury intrusion experiments on rock reservoir samples with different void structures to obtain the mercury saturation per unit pressure and the permeability of different samples.

In this step, samples at different depths are selected, and mercury injection experiments are performed on each sample respectively to obtain the permeability K of core samples at different depths; The unit pressure mercury injection saturation SHg/Pc under pressure, where SHg is the mercury injection saturation, and Pc is the mercury injection pressure.

3) By comparing the maximum unit pressure mercury saturation of each sample, a high-precision functional relationship between the maximum unit pressure mercury saturation and permeability is established.

The high-precision functional relationship between the maximum unit pressure mercury saturation (SHg/Pc)max and the permeability K is as follows:

K=f((SHg/Pc)max) (1)

4) Based on the high-precision functional relationship, a formula for calculating the permeability of carbonate reservoirs with the maximum unit pressure mercury saturation (SHg/Pc)max as the parameter is established.

The main expressions of the calculation formula are:

K=b(SHg/Pc)maxd (2)

In the formula, b and d are both constants.

The beneficial effect of the method for characterizing the permeability of carbonate rock reservoirs implemented by the present invention is: by determining the pore size boundary of the pore throat radius that can be characterized by both the adsorption method and the high-pressure mercury intrusion method, the pore size boundary of the pore throat radius that can be characterized by the adsorption method will be measured by the adsorption method. The pore structure below the pore size boundary and the pore structure above the pore size boundary measured by the high-pressure mercury intrusion method can be used to characterize the pore structure characteristics of the full pore size section, and the characterization results are more accurate. have a positive effect.

Claims (4)

1. A characterization method based on the permeability of a carbonate reservoir, which is special in that it comprises the following steps: 1) By determining the pore size boundary of the pore throat radius that can be characterized by adsorption method and high pressure mercury porosimetry, the pore structure below the pore size boundary measured by adsorption method and the pore structure above the pore boundary measured by high pressure mercury porosimetry are spliced. , to obtain the pore structure characteristics of carbonate reservoirs; 2) Perform mercury intrusion experiments on rock reservoir samples with different void structures to obtain the mercury saturation per unit pressure and the permeability of different samples; 3) By comparing the maximum unit pressure mercury saturation of each sample, a high-precision functional relationship between the maximum unit pressure mercury saturation and permeability is established; 4) Based on the high-precision functional relationship, a formula for calculating the permeability of carbonate reservoirs with the maximum unit pressure mercury saturation as the parameter is established. 2. The method for characterizing the permeability of carbonate reservoirs according to claim 1, characterized in that: said step 1) the method for determining the pore size boundary comprises the following steps: The high-pressure mercury injection test was performed on the shale sample to obtain the relationship between the first capillary pressure and the first pore throat radius; the adsorption method was performed on the shale sample to obtain the relationship between the second capillary pressure and the second pore throat radius And the first pore throat radius corresponding when the first capillary pressure in the described high pressure mercury injection test is increased sharply is determined as R1; The second pore throat radius corresponding when the second capillary pressure in the described adsorption method test is increased sharply is determined is R2; R1=R2=the aperture boundary. 3. the characterization method based on the permeability of carbonate rock reservoir according to claim 1, it is characterized in that: the functional relationship of high precision between maximum unit pressure mercury saturation and permeability in described step 3) for: K=f((SHg/Pc)max) In the formula, K is the permeability, SHg is the mercury injection saturation, Pc is the mercury injection pressure, (SHg/Pc)max is the maximum unit pressure mercury injection saturation, and f represents the functional relationship. 4. the characterization method based on the permeability of carbonate rock reservoir according to claim 1, is characterized in that: in step 4) in the complex carbonate rock reservoir permeability with maximum unit pressure mercury injection saturation as parameter The formula for calculating the rate is: K=b(SHg/Pc)maxd In the formula, K is the permeability, (SHg/Pc)max is the maximum unit pressure mercury saturation, and b and d are both constants.