CN112647933A - Method for measuring resistivity of water-bearing stratum - Google Patents
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Abstract
The disclosure discloses a method for measuring resistivity of a water-bearing stratum, and belongs to the field of petroleum gas exploration. The measuring method comprises the following steps: drilling a reference core in a target water-bearing stratum; measuring to obtain the matrix porosity of the reference rock core; adjusting the water saturation of the reference core, and measuring to obtain the matrix resistivity corresponding to the reference core under different water saturation; determining a corresponding relation between the matrix porosity and the matrix resistivity of the reference core; drilling a sample core in a target water-bearing formation; taking a matrix block on a sample core; obtaining the matrix resistivity of the matrix block through the matrix porosity conversion of the matrix block; measuring to obtain the karst cave resistivity of the sample rock core; and determining the resistivity of the target water-bearing stratum according to the karst cave resistivity of the sample core and the matrix resistivity of the sample core. And calculating to obtain the resistivity of the target water-bearing stratum. The method can quickly and simply measure the resistivity of the water-bearing stratum under different cavern porosities.
Description
Technical Field
The disclosure belongs to the field of petroleum gas exploration, and particularly relates to a method for measuring resistivity of a water-bearing stratum.
Background
The resistivity of the water-bearing stratum is closely related to the lithology, and the difference of the resistivity among the water-bearing stratum can be researched by analyzing and comparing the lithology in each water-bearing stratum, particularly analyzing and comparing the physical properties of the pores of each water-bearing stratum.
In recent years, with the rapid development of digital core technology, the resistivity is calculated through the characteristic parameters of the pore structure of rock, which is a widely advocated mode in the core physics community. In the related technology, a random network model is constructed by extracting the pore structure characteristics of rocks, then the voltage field distribution is solved by adopting super-relaxation iteration through a Kirchoff current law, and then the resistivity value of the reservoir is calculated.
However, the above method is complicated to implement because it requires complicated programming and calculation, resulting in a large workload.
Disclosure of Invention
The embodiment of the disclosure provides a method for measuring the resistivity of a water-bearing stratum, which can quickly and simply measure the resistivity of the water-bearing stratum under different cavern porosities. The technical scheme is as follows:
the embodiment of the disclosure provides a measuring method of water-bearing formation resistivity, which comprises the following steps:
drilling a reference core in a target water-containing stratum, wherein the reference core does not contain a karst cave;
determining a corresponding relation between the matrix porosity of the reference core and the matrix resistivity of the reference core according to the matrix porosity of the reference core and the matrix resistivity of the reference core corresponding to different water saturations;
drilling a sample core in the target water-bearing formation;
taking a matrix block on the sample core, wherein the matrix block does not contain a karst cave;
determining the matrix resistivity of the matrix block according to the matrix porosity of the matrix block based on the corresponding relation, and determining the matrix resistivity of the matrix block as the matrix resistivity of the sample core;
and determining the resistivity of the target water-bearing stratum according to the karst cave resistivity of the sample core and the matrix resistivity of the sample core.
Optionally, the determining, according to the matrix porosity of the reference core and the matrix resistivity of the reference core corresponding to different water saturations, a corresponding relationship between the matrix porosity of the reference core and the matrix resistivity of the reference core includes:
measuring to obtain the matrix porosity of the reference core;
adjusting the water saturation of the reference core, and measuring to obtain the corresponding matrix resistivity of the reference core under different water saturation;
determining the matrix resistivity of the reference core under 100% water saturation and the matrix resistivity of the reference core under different matrix porosities according to the matrix porosity of the reference core and the matrix resistivity of the reference core under different water saturations;
and determining the matrix resistivity corresponding to the reference core under the condition of 100% water saturation and different matrix porosities as the corresponding relation between the matrix porosity of the reference core and the matrix resistivity of the reference core.
Optionally, the determining the resistivity of the target water-bearing formation according to the cavern resistivity of the sample core and the matrix resistivity of the sample core includes:
establishing a grid system composed of a plurality of grid cells such that a volume of the grid system is equal to a volume of the sample core;
assigning the resistivity of each of the grid cells to a matrix resistivity of the matrix block;
measuring to obtain the karst cave resistivity of the sample rock core;
determining the cavern porosity of the sample core, and reassigning the resistivities of the grid units to be the cavern resistivity of the sample core according to the cavern porosity;
and determining the resistivity of the target water-bearing stratum according to the assigned grid system.
Optionally, the establishing a grid system composed of a plurality of grid cells such that a volume of the grid system is equal to a volume of the sample core includes:
determining a unit karst cave in the sample core, wherein the unit karst cave is the karst cave with the smallest volume in the sample core;
determining the grid cells, wherein the volume of the grid cells is equal to that of the cell caverns;
establishing a plurality of the grid cells into the grid system, the grid system including n rows and n columns of the grid cells, such that a volume of the grid system is equal to a volume of the sample core.
Optionally, the determining unit caverns in the sample core comprises:
obtaining a pore size distribution curve of the sample core;
and selecting the smallest karst cave in the sample core as a unit karst cave in the sample core according to the pore size distribution curve of the sample core.
Optionally, the determining the cavern porosity of the sample core comprises:
assigning a total porosity of the sample core;
and obtaining the cavern porosity of the sample core according to the difference between the total porosity of the sample core and the matrix porosity of the matrix block.
Optionally, the reassigning the resistivities of the grid cells to the cavern resistivity of the sample core according to the cavern porosity includes:
obtaining the number of grid units needing to be reassigned in resistivity by the product of the total number of the grid units and the porosity of the karst cave in the sample rock core:
selecting grid cells from the grid system for which resistivity needs to be reassigned;
and assigning the selected grid unit as the karst cave resistivity of the sample rock core.
Optionally, the selecting the grid cell of which resistivity needs to be reassigned from the grid system includes:
randomly selecting grid cells in the grid system that require resistivity reassignment.
Optionally, the determining the resistivity of the target water-bearing formation according to the assigned grid system includes:
and calculating the resistivity of the target water-bearing stratum by the following formula:
wherein R isijIs the resistivity, R, of the grid cell in row i and column josAnd (3) taking the resistivity of the target water-bearing stratum, wherein i is the row sequence number of the grid unit, j is the column sequence number of the grid unit, i is 1, 2, 3, … … and n, j is 1, 2, 3, … … and n, and n is a positive integer.
Optionally, said determining a matrix resistivity of said matrix block from a matrix porosity of said matrix block based on said correspondence comprises:
determining the corresponding matrix resistivity of the matrix block under different matrix porosities based on the corresponding relation;
and converting the matrix resistivity of the matrix block according to the matrix resistivity corresponding to the matrix block under different matrix porosities and the following formula:
wherein l is more than or equal to 2 and less than or equal to n, phiαIs the matrix porosity, phi, of the matrix mass0Is the matrix porosity, R, of the reference corem(Swl) As the water saturation is SwlMatrix resistivity, R, of the reference corem(Swl-1) As the water saturation is Swl-1The matrix resistivity, R, of the reference coremIs the matrix resistivity of the matrix mass.
The technical scheme provided by the embodiment of the disclosure has the following beneficial effects:
when the resistivity of the water-bearing stratum is measured by the measuring method provided by the embodiment of the disclosure, the reference core is drilled in the target water-bearing stratum, and the reference core does not contain a karst cave, namely, the reference core is completely a matrix, so that the porosity and the resistivity of the matrix of the reference core can be conveniently measured in the subsequent steps. And measuring to obtain the matrix porosity of the reference core, adjusting the water saturation of the reference core, and measuring to obtain the matrix resistivity corresponding to the reference core under different water saturations, so that the relationship between the matrix porosity and the matrix resistivity of the reference core can be conveniently obtained through conversion in the subsequent steps. Since the reference core has only matrix porosity, it is believed that the water in the reference core is substantially in the matrix porosity, and the matrix resistivity of the reference core is correlated to the matrix porosity of the reference core. That is, the higher the porosity of the matrix of the reference core, the higher its water saturation, and the lower the corresponding resistivity of the matrix.
Through the relation, the matrix resistivity corresponding to different matrix porosities can be obtained through conversion according to the matrix porosity of the reference core and the matrix resistivity corresponding to the reference core under different water saturations. And then, performing linear calculation on the matrix resistivity of the matrix block in the sample core by referring to the corresponding relation between the matrix porosity and the matrix resistivity of the core. And finally, determining the resistivity of the target water-bearing stratum according to the karst cave resistivity of the sample core and the matrix resistivity of the sample core. That is, the present disclosure establishes a correspondence between the matrix porosity and the matrix resistivity by referring to the core, and then calculates the matrix resistivity of the matrix block in the sample core through the correspondence, so that the resistivity of the target aquifer can be found by combining the measured karst cave resistivity. The method can quickly and simply measure the resistivity of the water-bearing stratum under different cavern porosities.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present disclosure, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.
FIG. 1 is a flow chart of a method of measuring resistivity of a aquifer provided by an embodiment of the disclosure;
FIG. 2 is a flow chart of a method of another method of measuring resistivity of a water-bearing formation provided by an embodiment of the present disclosure;
FIG. 3 is a schematic illustration of a particle size distribution of a cavern in a sample core provided by an embodiment of the disclosure;
FIG. 4 is a schematic structural diagram of a grid system provided by an embodiment of the present disclosure;
fig. 5 is a graph of a corresponding relationship between a ratio of different matrix porosities and cavern porosity of a core sample No. 1 provided in an embodiment of the present disclosure and resistivity of a study object.
Detailed Description
To make the objects, technical solutions and advantages of the present disclosure more apparent, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.
Fig. 1 is a flowchart of a method for measuring resistivity of a water-bearing formation according to an embodiment of the present disclosure, where the method for measuring resistivity of a water-bearing formation includes:
s101: and drilling a reference core in the target water-containing stratum, wherein the reference core does not contain a karst cave.
S102: and determining the corresponding relation between the matrix porosity of the reference core and the matrix resistivity of the reference core according to the matrix porosity of the reference core and the matrix resistivity of the reference core corresponding to different water saturations.
S103: a sample core is drilled in a target water-bearing formation.
S104: and taking a matrix block on the sample rock core, wherein the matrix block does not contain the karst cave.
S105: and determining the matrix resistivity of the matrix block according to the matrix porosity of the matrix block based on the corresponding relation, and determining the matrix resistivity of the matrix block as the matrix resistivity of the sample core.
S106: and determining the resistivity of the target water-bearing stratum according to the karst cave resistivity of the sample core and the matrix resistivity of the sample core.
When the resistivity of the water-bearing stratum is measured by the measuring method provided by the embodiment of the disclosure, the reference core is drilled in the target water-bearing stratum, and the reference core does not contain a karst cave, namely, the reference core is completely a matrix, so that the porosity and the resistivity of the matrix of the reference core can be conveniently measured in the subsequent steps. And measuring to obtain the matrix porosity of the reference core, adjusting the water saturation of the reference core, and measuring to obtain the matrix resistivity corresponding to the reference core under different water saturations, so that the relationship between the matrix porosity and the matrix resistivity of the reference core can be conveniently obtained through conversion in the subsequent steps. Since the reference core has only matrix porosity, it is believed that the water in the reference core is substantially in the matrix porosity, and the matrix resistivity of the reference core is correlated to the matrix porosity of the reference core. That is, the higher the porosity of the matrix of the reference core, the higher its water saturation, and the lower the corresponding resistivity of the matrix.
Through the relation, the matrix resistivity corresponding to different matrix porosities can be obtained through conversion according to the matrix porosity of the reference core and the matrix resistivity corresponding to the reference core under different water saturations. And then, performing linear calculation on the matrix resistivity of the matrix block in the sample core by referring to the corresponding relation between the matrix porosity and the matrix resistivity of the core. And finally, determining the resistivity of the target water-bearing stratum according to the karst cave resistivity of the sample core and the matrix resistivity of the sample core. That is, the present disclosure establishes a correspondence between the matrix porosity and the matrix resistivity by referring to the core, and then calculates the matrix resistivity of the matrix block in the sample core through the correspondence, so that the resistivity of the target aquifer can be found by combining the measured karst cave resistivity. The method can quickly and simply measure the resistivity of the water-bearing stratum under different cavern porosities.
Fig. 2 is a flowchart of another method for measuring resistivity of a water-bearing formation according to an embodiment of the present disclosure, and as shown in fig. 2, the measuring method includes:
s201: and drilling a reference core in the target water-containing stratum, wherein the reference core does not contain a karst cave.
It is readily understood that the matrix resistivity in the target water-bearing formation is substantially uniform, and the reference core without caverns is chosen to facilitate indirect investigation of the matrix resistivity of the sample core by studying the reference core.
S202: the matrix porosity of the reference core was measured.
Illustratively, the matrix porosity of the reference core is measured by injecting a medium into the reference core, that is, by measuring the volume of the medium injected into the reference core and the volume of the reference core, the ratio of the volume of the medium in the volume of the reference core is determined, and this ratio is the matrix porosity of the reference core.
S203: and adjusting the water saturation of the reference core, and measuring to obtain the matrix resistivity corresponding to the reference core under different water saturations.
Illustratively, the resistivity value of the reference core was measured as Ro when the water saturation was adjusted to 100%. As the water saturation Sw of the reference core changes, the value of the core resistivity rm (Sw) at that time is recorded. Namely: when the water saturation is Sw1At this time, the reference core resistivity value is Rm (Sw)1) (ii) a When the water saturation is Sw2At this time, the reference core resistivity value is Rm (Sw)2) (ii) a By analogy, when the water saturation is SwnAt this time, the reference core resistivity value is Rm (Sw)n)。
The reference core resistivity is obtained by detection according to the SY/T5385-2007 rock resistivity parameter laboratory measurement and calculation method in the industry standard.
The method for adjusting the water saturation of the reference core comprises the following steps:
a. the reference core was evacuated.
b. And (4) injecting water into the reference core to ensure that the water saturation of the reference core reaches 100%.
c. And injecting gas into the reference core to ensure that the water saturation of the reference core is the same as the adjustment value.
S204: and determining the matrix resistivity of the reference core at 100% water saturation and different matrix porosities according to the matrix porosity of the reference core and the matrix resistivity of the reference core at different water saturations.
S205: and determining the matrix resistivity corresponding to the reference core under the condition of 100% water saturation and different matrix porosities as the corresponding relation between the matrix porosity of the reference core and the matrix resistivity of the reference core.
It should be noted that the non-aqueous part of the reference core is regarded as an insulator, and the porosity of the corresponding reference core is phioThe reference core resistivity with 100% water saturation is Ro. Porosity of corresponding reference core is phi o Sw1At 100% water saturation, the reference core resistivity is Rm (Sw)1). And analogizing in turn, wherein the porosity of the corresponding reference core is phi o SwnAt 100% water saturation, the reference core resistivity is Rm (Sw)n)。
That is, the matrix porosity of the reference core and the matrix resistivity of the reference core corresponding to different water saturations can be converted to obtain the matrix resistivity corresponding to different matrix porosities at 100% water saturations. Preparing a conversion table between the matrix porosity and the matrix resistivity of the reference core, wherein the conversion table of the reference core can show the corresponding relation between the matrix porosity and the matrix resistivity, and the specific relation is shown in the following table 1:
table 1 reference the correspondence between matrix porosity and matrix resistivity in the core
S206: a sample core is drilled in a target water-bearing formation.
In the above embodiments, drilling the sample core in the target water-bearing formation may ensure that the matrix resistivities of the sample core and the reference core are substantially consistent.
S207: and taking a matrix block on the sample rock core, wherein the matrix block does not contain the karst cave.
In the above embodiment, the resistivity of the water-bearing formation of the sample core at different cavern porosities is studied by changing the matrix porosity of the matrix block, thereby changing the matrix porosity of the sample core.
S208: and determining the matrix resistivity of the matrix block according to the matrix porosity of the matrix block based on the corresponding relation, and determining the matrix resistivity of the matrix block as the matrix resistivity of the sample core.
Step S208 includes:
i: and determining the corresponding matrix resistivity of the matrix block under different matrix porosities based on the corresponding relation.
ii: the matrix resistivity of the matrix block is obtained through conversion according to the matrix resistivity corresponding to the matrix block under different matrix porosities and the following formula:
Wherein l is more than or equal to 2 and less than or equal to n, phiαIs the porosity of the matrix mass, phi0Porosity of matrix for reference core，Rm(Swl) As the water saturation is SwlMatrix resistivity, R, of reference corem(Swl-1) As the water saturation is Swl-1Matrix resistivity, R, of time reference coremIs the matrix resistivity of the matrix mass.
The substrate resistivity of the substrate block was calculated by performing linear calculation using the formula in S208.
S209: and determining a unit karst cave in the sample core, wherein the unit karst cave is the karst cave with the smallest volume in the sample core.
Step S209 further includes:
i. and acquiring a pore size distribution curve of the sample core.
Illustratively, the pore size distribution curve of the sample core is obtained by measuring the capillary pressure curve by CT scan, nuclear magnetic resonance, or mercury intrusion method.
ii. And selecting the smallest karst cave in the sample core as a unit karst cave in the sample core according to the pore size distribution curve of the sample core.
Fig. 3 is a schematic diagram of a particle size distribution of a cavern in a sample core provided by an embodiment of the disclosure, and a volume of a minimum cavern is determined by the particle size distribution of the cavern in the sample core as shown in fig. 3.
S210: and determining grid cells, wherein the volume of each grid cell is equal to that of the cell cavern.
It is easy to understand that the volume of the grid cell is equal to the volume of the cell cavern, i.e. the volume of the grid system is equal to the volume of a certain number of cell caverns.
S211: the plurality of grid cells is built into a grid system comprising n rows and n columns of grid cells such that the volume of the grid system is equal to the volume of the sample core (see fig. 4).
It is easily understood that since the location and number of the karst caves affect the resistivity of the sample core, n is established2The grid units are convenient for simulating the karst cave positions and the karst cave numbers of the sample rock core under different conditions, and then the resistivity of the sample rock core corresponding to different matrix porosities and different karst cave porosities is measured.
S212: the resistivity of each grid cell is assigned to the matrix resistivity of the matrix block.
S213: and measuring to obtain the karst cave resistivity of the sample core.
Step S213 includes:
i: and taking a karst cave block on the sample core, wherein the karst cave block contains the karst cave.
ii: and measuring the resistivity of the karst cave in the karst cave block.
S214: the total porosity of the sample core was assigned a value.
S215: and obtaining the cavern porosity of the sample core according to the difference between the total porosity of the sample core and the matrix porosity of the matrix block.
Specifically, the method comprises the following steps:
φc＝φ-φa；
in the above formula, phicIs the cavern porosity of the sample core, phi is the total porosity of the sample core, phiaIs the matrix porosity of the matrix mass.
S216: and obtaining the number of the grid units needing to be reassigned in resistivity by multiplying the total number of the grid units by the porosity of the karst cave in the sample rock core.
In the above embodiment, the number of the caverns in the sample core is determined by the product of the total number of the grid cells and the porosity of the caverns in the sample core.
S217: grid cells that require resistivity reassignment are randomly selected in the grid system.
It should be noted that the number of grid cells for which resistivity needs to be reassigned is the number of grid cells corresponding to the karst cave in the sample core. And the random assignment is to determine the position of the grid unit corresponding to the karst cave in the grid of the system, so that the position arrangement of the karst cave in the sample core is simulated through the grid system.
S218: and assigning the selected grid unit as the karst cave resistivity of the sample core.
S219: and calculating the resistivity of the target water-bearing stratum through a formula.
Specifically, the method comprises the following steps:
in the above formula, RijIs the resistivity of the grid cell, RosAnd i is the row sequence number of the grid unit, j is the column sequence number of the grid unit, i is 1, 2, 3, … … and n, j is 1, 2, 3, … … and n, and n is a positive integer.
It is easy to understand that the formula in step S219 means n in the sequential pair2And carrying out twice arithmetic mean on the grid resistivities of n rows and n columns in each grid unit, thereby approximately calculating the resistivity of the target aquifer.
When the resistivity of the water-bearing stratum is measured by the measuring method provided by the embodiment of the disclosure, the reference core is drilled in the target water-bearing stratum, and the reference core does not contain a karst cave, namely, the reference core is completely a matrix, so that the porosity and the resistivity of the matrix of the reference core can be conveniently measured in the subsequent steps. And measuring to obtain the matrix porosity of the reference core, adjusting the water saturation of the reference core, and measuring to obtain the matrix resistivity corresponding to the reference core under different water saturations, so that the relationship between the matrix porosity and the matrix resistivity of the reference core can be conveniently obtained through conversion in the subsequent steps. Since the reference core has only matrix porosity, it is believed that the water in the reference core is substantially in the matrix porosity, and the matrix resistivity of the reference core is correlated to the matrix porosity of the reference core. That is, the higher the porosity of the matrix of the reference core, the higher its water saturation, and the lower the corresponding resistivity of the matrix.
Through the relation, the matrix resistivity corresponding to different matrix porosities under 100% water saturation can be obtained through conversion according to the matrix porosity of the reference core and the matrix resistivity corresponding to the reference core under different water saturations, and a conversion table between the matrix porosity and the matrix resistivity is prepared. And then, carrying out linear calculation on the matrix resistivity of the matrix block in the sample core by referring to a conversion table between the matrix porosity and the matrix resistivity of the core, and assigning the calculated matrix resistivity and the calculated karst cave resistivity of the matrix block to the grid unit. And finally, calculating the resistivity of the target water-bearing stratum through a grid system. That is, the present disclosure may calculate the resistivity of the target aquifer by establishing a conversion table between the matrix porosity and the matrix resistivity with reference to the core, and then calculating the matrix resistivity of the matrix block in the sample core through the conversion table, thereby calculating the resistivity of the entire grid system in combination with the measured karst cave resistivity. The method can quickly and simply measure the resistivity of the water-bearing stratum under different cavern porosities.
The above steps are explained below with reference to actual data:
and taking a No. 1 sample core, and testing the resistivity of the water-bearing stratum under different cavern porosities by testing the curve of the rock pore size distribution characteristic and selecting a 30-by-30 grid system.
Selecting a No. 111 reference core of the core interval of the No. 1 sample, wherein the reference core does not contain a karst cave, testing the matrix porosity of the reference core to be 1.82%, and obtaining the matrix water saturation-resistivity relation shown in the table 2 through experiments.
Table 2111 reference core water saturation and matrix resistivity relation table
| Serial number | Water saturation% | Resistivity of matrix/omega.m | Porosity of |
| 1 | 100 | 76.198 | 1.82 |
| 2 | 90.3 | 96.471 | 1.64 |
| 3 | 75.4 | 123.459 | 1.37 |
| 4 | 51.7 | 196.402 | 0.94 |
| 5 | 35.6 | 375.269 | 0.65 |
Note that the non-aqueous portion of the core was considered as an insulator.
Illustratively, the resistivity of reference core # 111 at 90.3% water saturation was 96.471 Ω. m. Then, for cores with no caverns where the core matrix porosity reaches 1.64% (═ 0.0182 × 0.903)%, the core resistivity for 100% saturated water should likewise be 96.471 Ω · m. The resistivity of reference core No. 111 at 75.4% water saturation was 123.459 Ω. m. Then, for cores with no caverns where the core matrix porosity reaches 1.37% (═ 0.0182 × 0.754)% the core resistivity for 100% saturated water should likewise be 96.471 Ω · m, and so on.
It is to be noted that 100% saturation resistivity R in the core cavern of the No. 1 sample is obtained through testingw0.1206 Ω. m of formation water.
Since the porosity of the matrix of the reference core No. 111 is consistent with the porosity of the matrix of the sample No. 1, for different porosities of the matrix of the sample No. 1, the data of the porosity of the cavern, the number of the matrix meshes and the number of the cavern meshes are shown in tables 3, 4 and 5, and for different porosities of the matrix, the resistivity of the matrix is obtained according to the method shown in FIG. 1.
Assuming that the total porosity phi of the core sample No. 1 is 3%, the data of different matrix porosities, karst cave porosities, matrix grid numbers and karst cave grid numbers for different matrix blocks are shown in Table 3, and the matrix resistivity for different matrix blocks at different matrix porosities is obtained by the method shown in FIG. 1.
Table 3 table of relevant parameters for different matrix blocks different matrix porosities and cavern porosities (3%)
Assuming that the total porosity phi of the core sample No. 1 is 5%, the data of different matrix porosities, karst cave porosities, matrix grid numbers and karst cave grid numbers for different matrix blocks are shown in Table 4, and the matrix resistivity for different matrix blocks at different matrix porosities is obtained by the method shown in FIG. 1.
Table 4 table of relevant parameter values for different matrix blocks for different matrix porosities and cavern porosities (5%)
Assuming that the total porosity Φ of the core sample No. 1 is 7%, the data for different matrix porosities, cavern porosities, matrix lattice numbers, and cavern lattice numbers are shown in table 5, and the matrix resistivity for different matrix porosities is obtained as shown in fig. 1.
TABLE 5 correlation parameter value table (7%) for different matrix pieces, different matrix porosity and cavern porosity
As can be seen from tables 3, 4 and 5, the system resistivity corresponding to different matrix porosities and cavern porosities increases with the decrease of the matrix porosity under different total porosities of the core sample No. 1, i.e., the smaller the ratio of the matrix porosity to the cavern porosity (void ratio), the larger the system resistivity, i.e., the larger the resistivity of the target aquifer (see fig. 5).
As can be seen from fig. 5, under the same total porosity, the denser the matrix, the higher the resistivity of the study subject, the lower the porosity of the matrix, and the higher the resistivity of the study subject, thus indicating that the above test results are consistent with the prior knowledge.
The above description is only exemplary of the present disclosure and is not intended to limit the present disclosure, so that any modification, equivalent replacement, or improvement made within the spirit and principle of the present disclosure should be included in the scope of the present disclosure.
Claims (10)
1. A method of measuring resistivity of a water-bearing formation, the method comprising:
drilling a reference core in a target water-containing stratum, wherein the reference core does not contain a karst cave;
determining a corresponding relation between the matrix porosity of the reference core and the matrix resistivity of the reference core according to the matrix porosity of the reference core and the matrix resistivity of the reference core corresponding to different water saturations;
drilling a sample core in the target water-bearing formation;
taking a matrix block on the sample core, wherein the matrix block does not contain a karst cave;
determining the matrix resistivity of the matrix block according to the matrix porosity of the matrix block based on the corresponding relation, and determining the matrix resistivity of the matrix block as the matrix resistivity of the sample core;
and determining the resistivity of the target water-bearing stratum according to the karst cave resistivity of the sample core and the matrix resistivity of the sample core.
2. The measurement method according to claim 1, wherein the determining the correspondence between the matrix porosity of the reference core and the matrix resistivity of the reference core according to the matrix porosity of the reference core and the matrix resistivity of the reference core corresponding to different water saturations comprises:
measuring to obtain the matrix porosity of the reference core;
adjusting the water saturation of the reference core, and measuring to obtain the corresponding matrix resistivity of the reference core under different water saturation;
determining the matrix resistivity of the reference core under 100% water saturation and the matrix resistivity of the reference core under different matrix porosities according to the matrix porosity of the reference core and the matrix resistivity of the reference core under different water saturations;
and determining the matrix resistivity corresponding to the reference core under the condition of 100% water saturation and different matrix porosities as the corresponding relation between the matrix porosity of the reference core and the matrix resistivity of the reference core.
3. The measurement method according to claim 1, wherein determining the resistivity of the target water-bearing formation from the cavern resistivity of the sample core and the matrix resistivity of the sample core comprises:
establishing a grid system composed of a plurality of grid cells such that a volume of the grid system is equal to a volume of the sample core;
assigning the resistivity of each of the grid cells to a matrix resistivity of the matrix block;
measuring to obtain the karst cave resistivity of the sample rock core;
determining the cavern porosity of the sample core, and reassigning the resistivities of the grid units to be the cavern resistivity of the sample core according to the cavern porosity;
and determining the resistivity of the target water-bearing stratum according to the assigned grid system.
4. The measurement method according to claim 3, wherein the establishing a grid system of a plurality of grid cells such that a volume of the grid system is equal to a volume of the sample core comprises:
determining a unit karst cave in the sample core, wherein the unit karst cave is the karst cave with the smallest volume in the sample core;
determining the grid cells, wherein the volume of the grid cells is equal to that of the cell caverns;
establishing a plurality of the grid cells into the grid system, the grid system including n rows and n columns of the grid cells, such that a volume of the grid system is equal to a volume of the sample core.
5. The measurement method of claim 4, wherein the determining unit caverns in the sample core comprises:
obtaining a pore size distribution curve of the sample core;
and selecting the smallest karst cave in the sample core as a unit karst cave in the sample core according to the pore size distribution curve of the sample core.
6. The measurement method according to claim 3, wherein the determining the cavern porosity of the sample core comprises:
assigning a total porosity of the sample core;
and obtaining the cavern porosity of the sample core according to the difference between the total porosity of the sample core and the matrix porosity of the matrix block.
7. The measurement method according to claim 3, wherein the reassigning the resistivities of the grid cells to the cavern resistivity of the sample core according to the cavern porosity comprises:
obtaining the number of the grid units of which the resistivity needs to be reassigned by the product of the total number of the grid units and the porosity of the karst cave in the sample rock core;
selecting the grid cells from the grid system that require resistivity reassignment;
and assigning the selected grid unit as the karst cave resistivity of the sample rock core.
8. The method of measurement according to claim 7, wherein said selecting the grid cells from the grid system for which resistivity needs to be reassigned comprises:
randomly selecting the grid cells in the grid system that require resistivity reassignment.
9. The surveying method according to claim 3, wherein the determining the resistivity of the target aquifer from the assigned grid system comprises:
and calculating the resistivity of the target water-bearing stratum by the following formula:
wherein R isijIs the resistivity, R, of the grid cell in row i and column josAnd taking the resistivity of the target aquifer, wherein i is the row sequence number of the grid unit, j is the column sequence number of the grid unit, and i is 1, 2, 3, … …, n, j is 1, 2, 3, … …, nAnd n is a positive integer.
10. The method of measurement according to any one of claims 1-9, wherein the determining the matrix resistivity of the matrix block from the matrix porosity of the matrix block based on the correspondence comprises:
determining the corresponding matrix resistivity of the matrix block under different matrix porosities based on the corresponding relation;
and converting the matrix resistivity of the matrix block according to the matrix resistivity corresponding to the matrix block under different matrix porosities and the following formula:
Wherein l is more than or equal to 2 and less than or equal to n, phiαIs the matrix porosity, phi, of the matrix mass0Is the matrix porosity, R, of the reference corem(Swl) As the water saturation is SwlMatrix resistivity, R, of the reference corem(Swl-1) As the water saturation is Swl-1The matrix resistivity, R, of the reference coremIs the matrix resistivity of the matrix mass.
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Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN101649738A (en) * | 2008-08-13 | 2010-02-17 | 中国石油天然气集团公司 | Method for determining stratum water saturation |
| CN102434152A (en) * | 2011-12-05 | 2012-05-02 | 中国石油天然气股份有限公司 | Method for calculating oil saturation of reservoir |
| CN103422853A (en) * | 2012-05-24 | 2013-12-04 | 中国石油天然气集团公司 | Method and device for determining water saturation of stratum |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101649738A (en) * | 2008-08-13 | 2010-02-17 | 中国石油天然气集团公司 | Method for determining stratum water saturation |
| CN102434152A (en) * | 2011-12-05 | 2012-05-02 | 中国石油天然气股份有限公司 | Method for calculating oil saturation of reservoir |
| CN103422853A (en) * | 2012-05-24 | 2013-12-04 | 中国石油天然气集团公司 | Method and device for determining water saturation of stratum |
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