阅读说明：本技术 一种确定特高含水油藏可动油饱和度的方法 (Method for determining mobile oil saturation of ultrahigh water-cut oil reservoir ) 是由 王明 许寻 熊运斌 莫冰 张蕴曼 杨瑞敏 谢爱华 席伟安 于 2019-10-22 设计创作，主要内容包括：本发明属于油气田开发技术领域,具体涉及一种确定特高含水油藏可动油饱和度的方法。本发明的确定特高含水油藏可动油饱和度的方法主要包括以下步骤：根据高倍数水驱后的目标储层岩心样品的油相相对渗透率曲线以及水相相对渗透率曲线确定高倍数水驱后的残余油饱和度,然后根据高倍数水驱前的残余油饱和度以及高倍数水驱后的残余油饱和度确定可动油饱和度。本发明的方法精度高,可以反映特高含水期的渗流特征,并且可以应用于油田现场,为注水开发油藏方案的调整提供依据。(The invention belongs to the technical field of oil and gas field development, and particularly relates to a method for determining the mobile oil saturation of an ultrahigh water-cut oil reservoir. The method for determining the mobile oil saturation of the ultrahigh water-cut oil reservoir mainly comprises the following steps: and determining the residual oil saturation after the high-multiple water flooding according to the oil phase relative permeability curve and the water phase relative permeability curve of the target reservoir core sample after the high-multiple water flooding, and then determining the mobile oil saturation according to the residual oil saturation before the high-multiple water flooding and the residual oil saturation after the high-multiple water flooding. The method has high precision, can reflect the seepage characteristics of an ultrahigh water cut period, can be applied to an oil field, and provides a basis for adjusting a water injection oil reservoir development scheme.)

1. A method for determining the mobile oil saturation of an ultrahigh water-cut oil reservoir is characterized by comprising the following steps:

(1) washing oil from a core sample of a target reservoir, drying, then saturating water, and then preparing bound water from the saturated oil to obtain a core sample with certain water saturation; performing high-multiple water flooding on the core sample after the bound water is manufactured, and determining the relative permeability of an oil phase, the relative permeability of a water phase and the water saturation of the core sample after the high-multiple water flooding; the displacement multiple of the high multiple water flooding is at least 1000 pv;

(2) and (2) repeating the step (1) to determine the oil phase relative permeability, the water phase relative permeability data and the water saturation of the core sample after water flooding under different water saturations, then fitting the formula (I), determining coefficients a, b and c, and obtaining a relative permeability curve of the core sample:

ln(K_ro/K_rw)＝aS_w ²+bS_w+c (Ⅰ)

in formula (I): k_roRelative permeability of the oil phase, K_rwIs the relative permeability of the aqueous phase, S_wWater saturation, a, b and c are unitless coefficients;

(3) correcting the relative permeability of the oil phase and the relative permeability of the water phase under different water saturation degrees according to the fitted formula (I), and determining the residual oil saturation degree S after the water flooding of the ultrahigh water-cut oil reservoir_orh＝1-S_w；

(4) Residual oil saturation S after high multiple water flooding_orhAnd residual oil saturation S before high-multiple water flooding of ultra-high water-cut oil reservoir_orqDetermination of mobile oil saturation S for very high water cut reservoirs_d：S_d＝S_orq-S_orh。

2. The method for determining the mobile oil saturation of ultrahigh water content reservoir according to claim 1, wherein the residual oil saturation S before high power water flooding of ultrahigh water content reservoir in the step (4)_orqDetermined by the following method:

1) acquiring physical property parameters and fluid characteristic parameters of a target reservoir; the physical property parameters include permeability and porosity; the fluid characteristic parameters comprise formation crude oil viscosity and formation water viscosity;

2) determining the relative oil phase permeability and the relative water phase permeability of the target reservoir core sample under different water saturation degrees by using the physical property parameters and the fluid characteristic parameters;

3) determining a relative permeability curve according to the relative permeability of the oil phase and the relative permeability of the water phase obtained in the step 2), and then determining the residual oil saturation S before high-multiple water flooding of the ultrahigh water-cut oil reservoir by using the relative permeability curve_orq。

3. The method for determining the mobile oil saturation of the ultrahigh water content reservoir according to claim 1 or 2, wherein the displacement multiple of the high power water flooding in the step (1) is 1000 pv.

4. The method for determining the mobile oil saturation of the ultrahigh water content reservoir according to claim 2, wherein the water flooding factor when the relative permeability of the oil phase and the relative permeability of the water phase at different water saturation are determined in the step 2) is 20-50 pv.

5. The method for determining the mobile oil saturation of the ultrahigh water content reservoir according to claim 1, 2 or 4, wherein the porosity of the core sample is 0.2-0.3.

6. The method for determining mobile oil saturation of very high water cut reservoir according to claim 1, 2 or 4, characterized in that the relative permeability K of oil phase at different water saturation_roCalculated according to the following formula:wherein f is_o(S_w) The content of the oil is shown as the oil content,i is a value of relative injectability, I is a value of no such cumulative oil production.

7. The method for determining mobile oil saturation of very high water reservoir according to claim 6, wherein said oil cut f_o(S_w) Calculated according to the following formula:whereinIn order to have no value for the accumulated oil production,the value of dimensionless cumulative oil production.

8. The method for determining mobile oil saturation of an ultra high water reservoir according to claim 6, wherein the value of the relative injectivity, I, is calculated according to the following formula:wherein Q (t) is the value of the flow of the produced liquid at the outlet end face of the rock sample at the time t, Q_oIs the value of the flow of the produced liquid on the end face of the outlet of the rock core sample at the initial moment, delta p_oThe value of the initial driving pressure difference is Δ p (t), and the value of the driving pressure difference at the moment t is Δ p (t).

9. Method for determining mobile oil saturation of very high water cut reservoirs according to any of claims 1 or 2, characterized in that the relative permeability K of the aqueous phase at different water saturations_rwCalculated according to the following formula:f_o(S_w) Oil content, mu_wIs the formation water viscosity, mu_oIs the formation crude oil viscosity, K_roRelative permeability of the oil phase.

10. The method for determining mobile oil saturation of very high water reservoir according to claim 1, wherein the fitting of formula (i) is: ln (K)_ro/K_rw)＝-131.692S_w ²+164.615S_w-53.747, wherein K_roRelative permeability of the oil phase, K_rwIs the relative permeability of the aqueous phase, S_wThe water saturation.

Technical Field

The invention belongs to the technical field of oil and gas field development, and particularly relates to a method for determining the mobile oil saturation of an ultrahigh water-cut oil reservoir.

Background

After the oil field is developed by long-term water injection, the existing oil field enters into a development period with extremely high water content, the distribution rule of underground residual oil is searched, and corresponding potential excavation measures are made. The residual oil includes residual oil and mobile oil, wherein the residual oil refers to crude oil which can not be produced after water flooding and remains in the pores of an oil reservoir, and the mobile oil refers to oil which can flow in the reservoir under certain oil production process conditions and is partially produced from the oil reservoir. Although the movable oil after water flooding can not be completely produced from the reservoir, the main purpose of the residual oil after water flooding is to reduce the movable oil saturation after water flooding, so the movable oil saturation is an object for further adjusting the oil flooding of the reservoir and is also an important parameter in reservoir evaluation.

At present, the research on the movable oil saturation after water flooding mainly adopts an indoor core, and only the residual movable oil percentage of the core can be obtained by combining a nuclear magnetic resonance technology, a conventional mercury injection technology, an oil flooding water and a water flooding experiment. Zhang Tree Bao et al in research methods on residual oil saturation distribution (oil and gas field, 03 st 2000, pages 19-22) disclose a method for determining mobile oil saturation, comprising the following steps: making a relation curve of the oil-water relative permeability ratio and the water saturation on a semilogarithmic coordinate, and performing linear regression to obtain K_ro/K_rw＝ae^-bSw(ii) a Obtaining the water content f according to the oil-water diversion theory_w(ii) a Calculating water saturation S according to water content_w(ii) a Solving the saturation of the residual oil of the water drive according to the saturation of the water; obtaining water according to the saturation of the residual oilDisplacing oil saturation. In the calculation process of the method, the defects of mutual iterative calculation exist, and in addition, the precision is low. And the method can not be directly applied to the oil field site, and is inconvenient for the compilation and implementation of the oil reservoir engineering scheme.

Disclosure of Invention

The invention aims to provide a method for determining the mobile oil saturation of an ultrahigh water-cut oil reservoir, which can improve the accuracy of the obtained mobile oil saturation.

In order to achieve the purpose, the method for determining the mobile oil saturation of the ultrahigh water-cut oil reservoir adopts the technical scheme that:

a method for determining the mobile oil saturation of an ultrahigh water-cut oil reservoir comprises the following steps:

(1) washing oil from a core sample of a target reservoir, drying, then saturating water, and then preparing bound water from the saturated oil to obtain a core sample with certain water saturation; performing high-multiple water flooding on the core sample after the bound water is manufactured, and determining the relative permeability of an oil phase, the relative permeability of a water phase and the water saturation of the core sample after the high-multiple water flooding; the displacement multiple of the high multiple water flooding is at least 1000 pv;

(2) and (2) repeating the step (1) to determine the oil phase relative permeability, the water phase relative permeability data and the water saturation of the core sample after water flooding under different water saturations, then fitting the formula (I), determining coefficients a, b and c, and obtaining a relative permeability curve of the core sample:

ln(K_ro/K_rw)＝aS_w ²+bS_w+c (Ⅰ)

in formula (I): k_roRelative permeability of the oil phase, K_rwIs the relative permeability of the aqueous phase, S_wWater saturation, a, b and c are unitless coefficients;

(3) correcting the relative permeability of the oil phase and the relative permeability of the water phase under different water saturation degrees according to the fitted formula (I), and determining the residual oil saturation degree S after the water flooding of the ultrahigh water-cut oil reservoir_orh＝1-S_w；

(4) Residual oil saturation S after high multiple water flooding_orhAnd residual oil saturation S before high-multiple water flooding of ultra-high water-cut oil reservoir_orqDetermination of mobile oil saturation S for very high water cut reservoirs_d：S_d＝S_orq-S_orh。

The seepage rule and the characteristic of the ultrahigh water cut period are different from those of the medium-high water cut period, and the relative permeability ratio curve of the ultrahigh water cut period is obviously nonlinear, so that the water flooding characteristic curve of the ultrahigh water cut period is warped, and when the water flooding characteristic curve is warped, the traditional method for oil reservoir engineering is not applicable any more. The method quantitatively represents the residual oil saturation before and after the high-multiple water flooding by using the relative permeability data of the target reservoir before and after the high-multiple water flooding, thereby determining the mobile oil saturation of the ultrahigh water-cut oil reservoir. The method for determining the movable oil saturation degree has high precision, is suitable for the ultra-high water-containing oil reservoir, can be directly applied to the oil field, and is convenient for the establishment and implementation of the oil reservoir engineering scheme.

Residual oil saturation S before high-multiple water flooding of ultrahigh water-cut oil reservoir in step (4)_orqDetermined by the following method:

1) acquiring physical property parameters and fluid characteristic parameters of a target reservoir; the physical property parameters include permeability and porosity; the fluid characteristic parameters comprise formation crude oil viscosity and formation water viscosity;

2) measuring oil phase relative permeability data and water phase relative permeability data of the target reservoir core sample under different water saturation degrees by using the physical property parameters and the fluid characteristic parameters;

3) determining a relative permeability curve according to the relative permeability of the oil phase and the relative permeability of the water phase obtained in the step 2), and then determining the residual oil saturation S before high-multiple water flooding of the ultrahigh water-cut oil reservoir by using the relative permeability curve_orq。

Preferably, the displacement multiple of the high-multiple water flooding in the step (1) is 1000 pv.

Preferably, the water flooding factor when the relative permeability of the oil phase and the relative permeability of the water phase under different water saturation degrees are determined in the step 2) is 20-50 pv.

Preferably, the porosity of the core sample is 0.2-0.3.

Drawings

FIG. 1 is a graph of normalized oil-water relative permeability before high-power water flooding in an embodiment of the present disclosure;

FIG. 2 is a graph of normalized oil-water relative permeability after high-power water flooding in an embodiment of the present disclosure;

in fig. 1 and 2, curve i is the oil phase relative permeability curve and curve ii is the water phase relative permeability curve.

Detailed Description

The technical solution of the present invention is further illustrated by the following specific examples.

Example 1

Using the pu-cheng oil field sandw reservoir as an example, the following method was used to determine the mobile oil saturation of the reservoir:

firstly, determining the residual oil saturation before high-multiple water flooding

(1) Using a core sample from a pu-cheng oil field sand-two lower reservoir (permeability k 115mD), porosity was determined to be 0.214, length was 5cm, and radius was 2.5 cm;

(2) oil-water sample of Pucheng oil field sand reservoir is used for measuring viscosity mu of crude oil in stratum_o6.9 mPas, formation water viscosity μ_w1.34 mPas;

(3) placing the core sample subjected to oil absorption and drying into a core holder to saturate water, then adopting simulated oil with the same viscosity as the crude oil of the formation to drive water to prepare bound water, and measuring the relative permeability of the oil phase in the bound water state. And then performing water flooding (the water flooding multiple is 20-50 pv), and recording the water breakthrough time, the accumulated oil yield during water breakthrough, the accumulated liquid yield and the displacement differential pressure in the water flooding process.

(4) The relative permeability of the oil phase and the relative permeability of the water phase of the core sample at different saturation degrees can be obtained by the following formulas:

wherein: f. of_o(S_w) -values of oil content, expressed in decimal numbers;

-a value for dimensionless cumulative oil recovery, expressed as pore volume (V,r is the radius of the core sample, L is the length of the core sample,porosity of the core sample. ) Is expressed in multiples of (a);

-the value of the dimensionless cumulative fluid production expressed as a multiple of the pore volume;

K_ro-the numerical value of the relative permeability of the oil phase, expressed in decimal numbers;

K_rw-the value of the relative permeability of the aqueous phase, expressed in decimal units;

i-the value of relative injection capacity, also called flow capacity ratio;

rock sample outlet end face at time Q (t) -tThe flow rate of the produced liquid is expressed in cubic centimeters per second (cm)³/s)；

Q_o-value of the flow of the produced liquid at the end face of the rock sample outlet at the initial moment in cubic centimeters per second (cm)³/s)；

Δp_o-the value of the initial driving pressure difference in megapascals (MPa);

the value of the driving pressure difference at time Δ p (t) -t in megapascals (MPa);

S_we-a value of the water saturation at the outlet end face of the rock sample, expressed in decimal;

S_ws-number of irreducible water saturations, expressed in decimal.

The relative permeability of oil phase and the relative permeability of water phase of the core sample under different water saturation degrees are tested through a phase permeability experiment on the core sample in the reservoir, and the test results are shown in table 1.

TABLE 1 high-multiple water flooding prophase permeation experimental results

(5) Relative permeability curves were obtained from the relative permeability data in table 1 (as shown in figure 1). As can be seen from Table 1 and FIG. 1, the water saturation before high-power water flooding S_w10.7288, the residual oil saturation S before high multiple water flooding_orq＝1-S_w1＝0.2712。

Secondly, determining the residual oil saturation after high-multiple water flooding

(1) And washing the core sample with oil, drying, then saturating with water, and then preparing the bound water from the saturated oil.

(2) And (3) performing high-multiple water flooding on the core sample after the bound water is manufactured, wherein the displacement multiple is 1000pv, recording the water breakthrough time, the accumulated oil yield during the water breakthrough, the accumulated liquid yield and the displacement pressure difference in the water flooding process, and then obtaining the relative permeability of the oil phase and the relative permeability of the water phase under different water saturation degrees according to the formulas in the step (4) of determining the residual oil saturation degree before the high-multiple water flooding, wherein the relative permeability of the oil phase and the relative permeability of the water phase are shown in the table 2.

TABLE 2 high-multiple water flooding phase-permeation test results

Displacement multiple/pv	Water saturation/%	Relative permeability of oil phase (K)ro)	Relative permeability of aqueous phase (K)rw)
				0.34	0.385	1.0000	0.0000
1.25	0.436	0.4980	0.001
				2.84	0.569	0.1613	0.012
5.66	0.664	0.0100	0.022
				8.04	0.677	0.0072	0.025
11.22	0.698	0.0038	0.028
				24.92	0.719	0.0021	0.032
30.68	0.732	0.0014	0.034
				107.56	0.74	0.0011	0.035
353.79	0.755	0.0007	0.038
				588.10	0.762	0.0005	0.039
822.41	0.767	0.0005	0.04
				1001.92	0.778	0.0001	0.042

(3) And (3) fitting the data in the table (2) according to the formula (I) to obtain a phase permeation formula (II) reflecting the permeation characteristics in the ultra-high water-cut period.

ln(K_ro/K_rw)＝aS_w ²+bS_w+c (Ⅰ)

ln(K_ro/K_rw)＝-131.692S_w ²+164.615S_w-53.747 (Ⅱ)

(4) The relative permeability curve data of the corrected ultra-high water cut period obtained according to the formula (II) in the step (3) is shown in Table 3, and the phase permeability curve of the corrected ultra-high water cut period is shown in FIG. 2.

TABLE 3 corrected relative permeability data

Water saturation/%	Relative permeability of oil phase (K)ro)	Relative permeability of aqueous phase (K)rw)
			0.385	1	0
0.436	0.348	0.001
			0.569	0.122	0.012
0.664	0.01	0.022
			0.677	0.007	0.025
0.698	0.004	0.028
			0.719	0.0025	0.032
0.732	0.002	0.034
			0.74	0.0015	0.035
0.755	0.0009	0.038
			0.762	0.0008	0.039
0.767	0.0006	0.04
			0.778	0.0002	0.042
0.823	0.0001	0.042

As can be seen from FIG. 2, the water saturation S after high-multiple water flooding_w20.823, residual oil saturation after high power water flooding S_orh＝1-S_w2＝0.177。

Thirdly, determining the saturation of the movable oil

From the residual oil saturation before and after the high power water flooding, the mobile oil saturation S is known_d＝S_orq-S_orh0.2712-0.177-0.0942, i.e. the oil that can flow in a water-driving manner and is produced from the oil reservoir has a saturation of 0.0942.