CN106285654B - Method for judging capillary retention type oil reservoir - Google Patents

Abstract

The invention relates to a method for judging a capillary retention type oil reservoir. The method comprises the following steps of firstly, obtaining a lower limit value r of the pore throat radius of an oil field reservoir_minPore throat radius r of reservoir_thBuoyancy of the oil column in the reservoir F_bAnd capillary force F_cMinimum starting pressure gradient G of the reservoir_piAnd the buoyancy gradient G of the oil column_pbStep two, in r_th＞r_minWhen it is, F is judged_cAnd F_bAnd a size of G, and a judgment of G_piAnd G_pbStep three: at F_c＞F_bAnd G_pi＞G_pbAnd when the reservoir is a capillary retention type reservoir. According to the method, the type of the oil reservoir can be accurately judged, and the construction personnel can conveniently select the optimal exploitation mode. In addition, the basic parameters required by the method can be conveniently obtained, and the method is convenient for industrial popularization and application.

Description

Method for judging capillary retention type oil reservoir

Technical Field

The invention relates to the field of oil and gas field exploration and development, in particular to a method for identifying a capillary retention type oil reservoir.

Background

Before the development of the oil field, the type of the oil reservoir is determined to select the best exploitation mode. As can be seen from the conventional petroleum geology theory, rocks with poor physical properties, such as mudstone and other rocks with poor physical properties, seal an oil layer with good physical properties, i.e., a conventional oil reservoir. In a traditional oil reservoir, oil is distributed at the upper part and water is distributed at the bottom under the action of gravity differentiation.

However, as research progresses, a new reservoir type, namely a capillary retention reservoir, is discovered. In a capillary retention type oil reservoir, the conventional common sense of 'oil feeding and water discharging' is overturned, and the specific expression is that a water layer with better physical properties seals an oil layer with poorer physical properties, namely, the 'oil-in-water' condition of 'oil feeding and water discharging' occurs. The capillary retention type oil reservoir is widely distributed in China, and the discovery widens the new field of oil exploration and development.

Because the oil-water distribution mode in the capillary retention type oil reservoir is different from that of the traditional oil reservoir, the exploitation mode is greatly different. Therefore, before oil field development, the type of oil reservoir needs to be judged first to select the best exploitation mode.

Disclosure of Invention

Aiming at the problems, the invention provides a method for judging a capillary retention type oil reservoir. According to the method, the type of the oil reservoir can be accurately judged, and the construction personnel can conveniently select the optimal exploitation mode. In addition, the basic parameters required by the method can be conveniently obtained, and the method is convenient for industrial popularization and application.

The method of the invention comprises the following steps: step one, obtaining the pore throat radius r of an oil field reservoir_thLower limit value r of pore throat radius_minBuoyancy of oil column in reservoir F_bAnd capillary force F_cMinimum starting pressure gradient G of the reservoir_piAnd buoyancy gradient G of oil column_pbStep two, in r_th＞r_minWhen it is, F is judged_cAnd F_bAnd a size of G, and a judgment of G_piAnd G_pbStep three: at F_c＞F_bAnd G_pi＞G_pbAnd the reservoir is a capillary retention type reservoir.

According to the method, when judging whether the reservoir is a capillary retention type reservoir or not, r is judged firstly_thAnd r_minThe magnitude relationship of (1). This is because, from the aspect of oil preservation in the reservoir, the smaller the pore throat radius is, the larger the capillary pressure is, and the more favorable the formation of a capillary retention type reservoir by retarding oil migration. However, from the viewpoint of oil production, in order to enable oil production in the pores, the pore throat radius cannot be too small, and it is required to form a continuous oil phase and have a certain flow capacity in the pores, so that the pore throat radius r of the reservoir is large_thMust be larger than the lower limit value r of the pore throat radius_min. In addition, not only the capillary force F as a resistance is taken into account_cAnd oil column buoyancy F as power_bThe minimum starting pressure gradient G of the reservoir_piAnd buoyancy gradient G of oil column_pbAs an important parameter. The applicant has found that due to the oil column buoyancy F_bThe direction of action of (2) is towards the upward inclination of the inclined stratum, only using the buoyancy F of the oil column_bForce F with the capillary_cThe comparison can only judge whether the oil column moves along the upward inclined direction of the stratum, but cannot judge whether the oil column moves in other directions, so that only the buoyancy F of the oil column is used_bForce F with the capillary_cIt is not accurate to compare to determine whether the reservoir is a capillary retention reservoir. In the actual construction process, it was also confirmed that only the oil column buoyancy F was used_bAnd capillary force F_cWhen the type of the oil reservoir is judged, errors often occur. However, according to the method of the present invention, a minimum starting pressure gradient G of the reservoir is further introduced_piAnd buoyancy gradient G of oil column_pbAs a judgment condition, the accuracy of judgment is greatly improved.

In one embodiment, the buoyancy gradient G_pbThe oil-water density difference and the included angle between the seepage direction and the vertical direction are related. Buoyancy gradient G_pbIs represented by the following formula

In the formula, ρ_oIs the density of the oil, p_wIs the density of the water and is,

is the angle between the seepage direction and the vertical direction, rho_o，ρ_wAnd

can be obtained by logging data. In one embodiment, the minimum activation pressure gradient G_piObtained by core experiments. And the buoyancy gradient G_pbIt is indicative of the buoyancy experienced by the column of oil in various directions, not just in the direction of inclination of the inclined formation. Thus by judging G_piAnd G_pbThe size of the oil column can accurately judge whether the oil column does not generate seepage in all directions, so that whether the reservoir is a capillary retention type oil reservoir can be judged more accurately.

In one embodiment, the oil column buoyancy F_bRelated to oil-water density difference, formation dip angle and length of oil column. Specifically, the oil column buoyancy F_bIs represented by the following formula

F_b＝(ρ_w-ρ_o)×g×L×sinφ

In the formula, ρ_oIs the density of the oil, p_wIs the density of water, L is the length of the oil column in the direction of the formation inclination, phi is the formation inclination angle, rho_o，ρ_wBoth L and φ can be obtained from well log data.

In one embodiment, the capillary force F_cIs represented by the following formula

Wherein σ is the oil-water interfacial tension; theta is the surface wetting angle of water to the rock of the reservoir, and both sigma and theta can be obtained by core experiments.

Compared with the prior art, the invention has the advantages that: (1) will r is_thAnd r_minThe size relationship of (A) is used as a primary condition for judging the capillary retention type oil reservoir, so that the capillary half can be removedThe diameter is too small, and the reservoir with continuous oil phase can not be formed in the reservoir, thereby greatly simplifying the implementation of the method. (2) Buoyancy F of oil column in reservoir_bAnd capillary force F_cAnd minimum starting pressure gradient G of reservoir_piAnd buoyancy gradient G of oil column_pbAs the condition for judging the capillary retention type oil reservoir, the accuracy of judgment is greatly improved.

Drawings

The invention will be described in more detail hereinafter on the basis of embodiments and with reference to the accompanying drawings. Wherein:

FIG. 1 is a schematic representation of the steps for carrying out the method according to the invention, and

FIG. 2 is a plot of tubular retention reservoir distribution area versus log response determined in an embodiment of the present invention.

In the drawings, like parts are provided with like reference numerals.

Detailed Description

The present invention will be further explained with reference to the following examples and drawings.

Figure 1 schematically shows the steps for carrying out the method according to the invention. As shown in fig. 1, the method of the present invention comprises the following steps.

Step 11: obtaining the lower limit value r of the pore throat radius of the oil field_minPore throat radius r of reservoir_thBuoyancy of oil column in reservoir F_bAnd capillary force F_cMinimum starting pressure gradient G of the reservoir_piAnd buoyancy gradient G of oil column_pb。

Step 12: at r_th＞r_minWhen it is, F is judged_cAnd F_bAnd a size of G, and a judgment of G_piAnd G_pbThe size of (2).

Step 13: at F_c＞F_bAnd G_pi＞G_pbAnd the reservoir is a capillary retention type reservoir.

In step 11, the lower limit of the pore throat radius r is determined for different oil fields_minDifferent but determined for a determined field and can be measured by prior art methods, for exampleFor example, it can be obtained by mercury injection data and oil test data analysis. Pore throat radius r of reservoir_thThis can be done by taking a core sample from the reservoir and then testing it in the laboratory. Minimum starting pressure gradient G of reservoir_piFor example, by subjecting a core sample to darcy percolation experiments. Buoyancy of oil column F_bAnd capillary force F_cAnd a buoyancy gradient G_pbMay be calculated from the logging parameters as will be described in more detail below. The various methods described above are well known to those skilled in the art and will not be described in detail herein.

In one embodiment, the buoyancy gradient G_pbIs represented by the following formula

In the formula, ρ_oIs the density of the oil, p_wIs the density of the water and is,

is the angle between the seepage direction and the vertical direction, rho_o，ρ_wAnd phi can be obtained from well log data. Buoyancy gradient G_pbShowing the buoyancy effect experienced in different directions of the oil and not just in the direction of inclination of the inclined formation.

Buoyancy of oil column F_bIs represented by the following formula

F_b＝(ρ_w-ρ_o)×g×L×sinφ

In the formula, ρ_oIs the density of the oil, p_wIs the density of water, L is the length of the oil column in the direction of the formation inclination, phi is the formation inclination angle, rho_o，ρ_wBoth L and φ can be obtained from well log data. Capillary force F_cIs represented by the following formula

Wherein σ is the oil-water interfacial tension; theta is the surface wetting angle of water to the rock of the reservoir, and both sigma and theta can be obtained by core experiments.

Buoyancy of oil column F_bAnd capillary force F_cThe calculation of (c) is well known to those skilled in the art and the process of obtaining it is not discussed here.

Applicants have found that the storage state of oil within a reservoir can be divided into three categories. First, for a region with good physical properties, the radius of the capillary is large, the capillary force (i.e., resistance to oil movement) is small, and the free oil is more buoyant than the capillary force and can easily migrate upwards, thereby forming a traditional reservoir type. Secondly, for the poor region of rerum natura, the fine capillary develops, and the capillary force is great and is greater than the buoyancy that oil received, and oil gas can be detained in the poor reservoir of rerum natura to form capillary retention type oil reservoir. Thirdly, in the region of very poor physical properties, the radius of the capillary is too small, the resistance of the capillary is very large and the oil is prevented from flowing in the capillary, and the oil is difficult to flow out of the capillary to form a dry layer.

Based on the above classification, in step 12, first, r is determined_thAnd r_minThe size relationship of (2) to eliminate the dry layer, thereby greatly simplifying the step of judging whether the reservoir is a capillary retention type reservoir. It should be understood that the throat radius is a characteristic that characterizes the size of the capillary. At r_th＞r_minIn case of this, F is judged again_cAnd F_bAnd a size of G, and a judgment of G_piAnd G_pbThe size of (2).

In step 13, at F_c＞F_bAnd G_pi＞G_pbAnd the reservoir is a capillary retention type reservoir. Since step 13 is performed after step 12, the precondition r is implicitly included in step 13_th＞r_min。

From the above analysis, the oil column buoyancy F_bOnly the seepage driving force of the oil column in the direction of the inclination of the inclined stratum is shown. However, the seepage driving force of the oil column is also affected by other directions such as the vertical direction. Thus using the capillary force F_cAnd oil column buoyancy F_bMinimum starting pressure gradient G of reservoir_piAnd buoyancy gradient G of oil column_pbThe seepage capability of the oil column can be more accurately judged, and the type of the oil reservoir can be accurately judged。

Example 1:

at the T1 well zone, at zone 21 between reservoir depths 2270m to 2285m, pore throat radius r_thBetween 0.16 μm and 0.3 μm. Determining the pore throat radius lower limit value r of the reservoir according to the capillary pressure and the oil test data_minAnd was 0.16 μm. The length L of the oil column is between 100 and 300 m. The physical parameters of the reservoir are shown in table 1.

TABLE 1

From the above parameters, it can be seen that the capillary force F is in the region between the reservoir depths 2270m to 2285m of the T1 well_cBetween 0.0837 and 0.1599N, oil column buoyancy F_b0.0227-0.068N.

Thus, it can be seen that r_th＞r_minAnd F is_c＞F_b。

And the minimum starting pressure gradient G of the reservoir is measured by tests_piHas a minimum value of 0.05 MPa/m. And a gradient G of buoyancy in the vertical direction_pbAbout 0.0024MPa/m, much less than G_pi. In other directions, the buoyancy gradient G_pbSmaller and much smaller than G_pi. Thus, the reservoir has a buoyancy gradient G in all directions_pbLess than G_piI.e. G_pi＞G_pb。

That is, the region 21 between reservoir depths 2270m to 2285m of the T1 well complies with the rules: r is_th＞r_minAnd F is_c＞F_b，G_pi＞G_pb. Therefore, it is theoretically determined that the region 21 should be a capillary-retention reservoir.

FIG. 2 shows the actual log response. As is clear to those skilled in the art from figure 2, there is a region of sudden drop in resistivity between reservoir depths 2270m and 2285m without a corresponding significant change in the porosity curve 24. This means that the area 25 is a water area and the area 23 below the water area 25 is an oil area. That is, there is a capillary-retention reservoir of "top-bottom oil" between reservoir depths 2270m to 2285m, consistent with theoretical judgments in accordance with the method of the present invention.

While the invention has been described with reference to a preferred embodiment, various modifications may be made thereto without departing from the scope of the invention. It is intended that the invention not be limited to the particular embodiments disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims (5)

1. A method for judging a capillary retention type oil reservoir comprises the following steps,

step one, obtaining the pore throat radius r of an oil field reservoir_thLower limit value r of pore throat radius_minBuoyancy of the oil column in the reservoir F_bAnd capillary force F_cMinimum starting pressure gradient G of the reservoir_piAnd the buoyancy gradient G of the oil column_pb，

Step two, at r_th＞r_minWhen it is, F is judged_cAnd F_bAnd a size of G, and a judgment of G_piAnd G_pbThe size of (a) is (b),

step three: at F_c＞F_bAnd G_pi＞G_pbWhen the reservoir is a capillary retention type reservoir;

the buoyancy gradient G_pbIs represented by the following formula

In the formula, ρ_oIs the density of the underground oil, p_wWhich is the density of the groundwater,

is the angle between the seepage direction and the vertical direction, rho_o，ρ_wAnd

can be obtained by logging data.

2. The method of claim 1, wherein the minimum startup pressure gradient G_piObtained by core experiments.

3. The method of any one of claims 1 or 2, wherein the oil column buoyancy F_bRelated to oil-water density difference, formation dip angle and length of the oil column.

4. The method of claim 3, wherein the oil column buoyancy F_bIs represented by the following formula

F_b＝(ρ_w-ρ_o)×g×L×sinφ

In the formula, ρ_oIs the density of the oil, p_wIs the density of water, L is the length of the oil column in the direction of the formation inclination, phi is the formation inclination angle, rho_o，ρ_wBoth L and φ can be obtained from well log data.

5. The method of claim 1, wherein the capillary force F_cIs represented by the following formula

Wherein σ is the oil-water interfacial tension; theta is the surface wetting angle of water to the rock of the reservoir, and both sigma and theta can be obtained by core experiments.

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