CN-122016903-A - Calculation method of ultralow permeability reservoir water drive displacement limit

CN122016903ACN 122016903 ACN122016903 ACN 122016903ACN-122016903-A

Abstract

The invention relates to a calculation method of a water drive displacement limit of an ultralow permeability reservoir, which comprises the steps of S1, obtaining permeability K of a plurality of cores, S2, establishing a conversion model of nuclear magnetic resonance relaxation time and pore throat radius r of the cores, S3, calculating average pore throat radius of the cores according to the pore throat radius r and accumulated distribution frequency thereof And S4, acquiring displacement limits of a plurality of cores, S5, establishing a core displacement limit mathematical model, and calculating the displacement limit of the ultra-low permeability reservoir water injection development through the model. Aiming at the characteristics of the ultralow permeability reservoir, the invention establishes a displacement limit model by combining macroscopic physical parameters and microscopic pore throat characteristic parameters, can effectively predict the displacement limit of the water flooding development of the ultralow permeability reservoir, effectively guide the selection of the development mode of the ultralow permeability reservoir and support the scale benefit development of the ultralow permeability reservoir.

Inventors

CHEN LIN
WANG CHONG
SUN DONG
WANG DI
CHEN XIAODONG
LIU JIAN
XIE QICHAO
SHI JIANCHAO
ZHANG BAOJUAN
XU QIANWEN
SONG PENG
WANG JIN

Assignees

中国石油天然气股份有限公司

Dates

Publication Date: 20260512
Application Date: 20241112

Claims (10)

1. The method for calculating the ultra-low permeability reservoir water drive displacement limit is characterized by comprising the following steps of: s1, obtaining core samples of a plurality of wells of a target reservoir, and measuring the permeability K of each core after removing residual oil or slurry of the core samples; S2, according to a nuclear magnetic resonance T 2 spectrum curve in a core saturated water state, combining the core target reservoir high-pressure mercury injection curve to obtain a core nuclear magnetic resonance T 2 spectrum relaxation time and pore throat radius r conversion model; s3, converting a T 2 spectrum curve of the core into a high-pressure mercury curve according to a conversion model of nuclear magnetic resonance T 2 spectrum relaxation time and pore throat radius r of the core, and calculating the average pore throat radius of the core through the high-pressure mercury curve Coefficient of variation D r ; S4, respectively setting a plurality of different experimental flow rates for each rock core, carrying out a water flooding displacement test in a mode from low flow rate to high flow rate, and recording the recovery ratio eta when the pressure is stabilized at different flow rates, wherein when the recovery ratio of the rock core is not increased after the flow rate is increased, the recovery ratio is the displacement limit of the rock core; S5, constructing displacement characteristic indexes according to the permeability K obtained in the S1 and the variation coefficient D r obtained in the S3, fitting the displacement characteristic indexes of a plurality of cores with the displacement limit obtained in the S4, and carrying out regression to obtain a core displacement limit mathematical model, so that the displacement limit of the ultra-low permeability reservoir water injection development can be calculated through the model.
2. The method of computing an ultra-low permeability reservoir water flooding displacement limit of claim 1, further comprising: S6, according to a core displacement limit mathematical model and in combination with limit recovery efficiency eta kc in field production of an oil field, solving a displacement characteristic index T kc of the field, establishing an ultralow permeability reservoir water drive displacement limit plate according to combinations of different permeability, average pore throat radius and variation coefficients, and selecting a development mode according to the limit plate.
3. The method for calculating the water drive displacement limit of the ultralow permeability reservoir according to claim 1, wherein in S2, the nuclear magnetic resonance T 2 spectrum curve of the core in the saturated water state is obtained by preparing a core saturated CaCl 2 solution, and then placing the core saturated CaCl 2 solution into a nuclear magnetic resonance instrument for measurement.
4. The method for calculating the water drive displacement limit of the ultralow permeability reservoir according to claim 1, wherein the step S2 is a method for obtaining a conversion model of nuclear magnetic resonance relaxation time and pore throat radius r of the core by combining a high-pressure mercury curve of the core according to a nuclear magnetic resonance T 2 spectrum curve of the core in a saturated water state, and comprises the following steps: s201, drawing a cumulative distribution frequency curve of nuclear magnetic resonance T 2 according to a nuclear magnetic resonance T 2 spectrum curve of the core in a saturated water state, and drawing a cumulative distribution frequency curve of pore throat radius r according to a high-pressure mercury curve of the core; S202, interpolating an accumulated distribution frequency curve of the pore throat radius r according to the accumulated distribution frequency curve in an effective saturation interval, namely S pcd <S i <S Hgmax , by taking S=S i to obtain a pore throat radius r i when the accumulated distribution frequency is S i , and simultaneously obtaining values of T 2i and r i under the same accumulated distribution frequency S i ; Wherein S i is the cumulative distribution frequency corresponding to the radius r i of any pore throat, S Hgmax is the cumulative distribution frequency corresponding to the maximum mercury saturation, and S pcd is the cumulative distribution frequency corresponding to the displacement pressure; S203, the conversion relation between the nuclear magnetic resonance relaxation time of the core and the pore throat radius r is as follows: (I) Wherein ρ 2 is the transverse surface relaxation rate, μm·ms -1 ; Fs is the pore form factor; t 2 is the nuclear magnetic resonance relaxation time of the core; C is a conversion coefficient; n is a power exponent; S204, fitting regression is carried out on T 2 and r under different cumulative distribution frequencies S of the core to obtain C, n values, and C, n average values are obtained according to fitting regression of a plurality of cores, so that a conversion model of nuclear magnetic resonance T 2 spectrogram relaxation time and pore throat radius r of the target reservoir can be obtained.
5. The method for calculating a water drive displacement limit of an ultra-low permeability reservoir according to claim 1 or 4, wherein in step S203, the method for obtaining the conversion relationship between the core nmr relaxation time and the pore throat radius r is as follows: a. The relaxation time T 2 of the fluid in the pores of the porous medium in an ideal uniform magnetic field can be expressed as: (II) Wherein S is the surface area of a single pore, mum 2 ; V is the volume of a single pore, μm 3 ; b. the relation between the specific surface and the pore diameter is as follows: (III) wherein Fs is a pore shape factor, r is pore throat radius, mum; c. substituting the relation formula III of the specific surface and the aperture into formula II to obtain formula IV (IV) D. Due to the complexity of the pore throat structure in the actual reservoir, the experimental results are summarized to find that the nuclear core nuclear magnetic resonance relaxation time and the pore throat radius are not in a linear relation, but in a power function relation, so that the conversion relation between the nuclear core nuclear magnetic resonance T 2 spectrogram relaxation time and the pore throat radius r is obtained as follows: (I)。
6. The method for calculating a water drive displacement limit of an ultra-low permeability reservoir according to claim 1, wherein in S3, the average pore throat radius of the core is The coefficient of variation Dr is calculated as follows: (V) (VI) wherein: is the average pore throat radius, μm; r i 、r i+1 is the radius of any hole throat; S Hgi is the cumulative distribution frequency corresponding to the pore throat radius r i ,%; S Hgi+1 is the cumulative distribution frequency corresponding to the pore throat radius r i+1 ,%; Δs Hgi corresponds to r i and the average pore throat radius Cumulative distribution frequency difference in intervals,%; r is the pore throat radius; D r is the coefficient of variation.
7. The method for calculating a water drive displacement limit of an ultra-low permeability reservoir according to claim 1, wherein in S5, the formula for calculating the displacement characteristic index is: (VII) Wherein T is a displacement characteristic index; K is permeability; Is the average pore throat radius; D r is the coefficient of variation.
8. The method for calculating a water drive displacement limit of an ultra-low permeability reservoir according to claim 1, wherein in S5, the method for establishing the mathematical model of the core displacement limit is as follows: And fitting regression is carried out by adopting a production function mode by taking the displacement characteristic index as an abscissa and the displacement limit as an ordinate, so that the core displacement limit mathematical model can be obtained.
9. The method of computing an ultra-low permeability reservoir water flooding displacement limit according to claim 1 or 7, wherein the core displacement limit mathematical model is: (VIII) Wherein eta is a displacement limit; T is a displacement characteristic index; e is a natural constant, 2.71; a. b, c represent fitting parameters.
10. The method for calculating the displacement limit of the ultra-low permeability reservoir water drive according to claim 2, wherein in S6, the specific method for establishing the displacement limit plate of the ultra-low permeability reservoir water drive and selecting the development mode according to the limit plate comprises the steps of combining the ultimate recovery efficiency eta kc in the on-site production of oil reservoirs to obtain the on-site displacement characteristic index T kc , and according to the permeability K and the average pore throat radius of different oil reservoirs Calculating a characteristic index T by a combination of the variation coefficients D r , when the characteristic index T of any combination is larger than or equal to T kc , the combination is suitable for water flooding development of the oil reservoir, when the characteristic index T of any combination is smaller than T kc , the combination is unsuitable for water flooding development of the oil reservoir, and meanwhile, collecting calculation results of the characteristic indexes to manufacture a water flooding displacement limit plate.

Description

Calculation method of ultralow permeability reservoir water drive displacement limit Technical Field The invention belongs to the field of oil and gas field development, and particularly relates to a calculation method of an ultralow permeability reservoir water drive displacement limit. Background Along with the gradual transition of a long-term-day oilfield development object from an ultralow permeability I type to an ultralow permeability II and III type with denser reservoir conditions (the permeability/average permeability of the ultralow permeability I type reservoir is more than or equal to 0.5 multiplied by 10 -3μm2, the permeability of the ultralow permeability II type reservoir is 0.3-0.5 multiplied by 10 -3μm2, the permeability of the ultralow permeability III type reservoir is less than or equal to 0.3 multiplied by 10 -3μm2), part of the ultralow permeability reservoir shows the problems of larger development difficulty, no effect of water injection displacement, quick yield decrement and the like, a larger gap exists between the development effect and the evaluation expectation, and the conventional displacement limit evaluation method adopting the pore permeability parameter as an index cannot meet the actual requirements of the development of the current ultralow permeability II and III type reservoirs. Therefore, researching a comprehensive displacement limit characterization method of a reservoir, and optimizing a proper technical policy has very important significance for the development of an ultra-low permeability reservoir. The displacement limit calculation method commonly used at present generally adopts a water flooding characteristic curve method, namely, the water flooding development effect evaluation and the displacement limit prediction are carried out through an oil-water relation curve in the oil reservoir production process of water flooding development. The water flooding characteristic curve method divides an oil reservoir production curve into four water flooding types of A, B, C and T according to the oil-water relationship, different production characteristics of the oil reservoir are reflected, a water flooding characteristic fitting chart is drawn through the relationship between the water saturation and the recovery ratio under the water flooding curve, and further a displacement limit is predicted, but because the method is adopted to predict the displacement limit of the oil reservoir, a longer production time is required for fitting the water flooding characteristic chart, and if the oil reservoir production time is shorter, the fitting precision is lower. For the new area production of the ultralow permeability oil reservoir, because the oil reservoir lacks long-time production data in the initial development stage, the displacement limit error of the oil reservoir is predicted by adopting a water-flooding characteristic curve method to be larger, and the current requirement of the development of the ultralow permeability oil reservoir cannot be met. Disclosure of Invention In order to overcome the defects in the prior art, the invention aims to combine physical properties of an ultralow permeability reservoir with pore-throat characteristic parameters, provide a calculation method of an ultralow permeability reservoir water-flooding displacement limit, and further guide formulation of an ultralow permeability reservoir development technical policy. In order to achieve the above purpose, the technical scheme adopted by the invention is as follows: a calculation method of an ultralow permeability reservoir water drive displacement limit comprises the following steps: s1, obtaining core samples of a plurality of wells of a target reservoir, and measuring the permeability K of each core after removing residual oil or slurry of the core samples; S2, according to a nuclear magnetic resonance T 2 spectrum curve in a core saturated water state, combining the core target reservoir high-pressure mercury injection curve to obtain a core nuclear magnetic resonance T 2 spectrum relaxation time and pore throat radius r conversion model; s3, converting a T 2 spectrum curve of the core into a high-pressure mercury curve according to a conversion model of nuclear magnetic resonance T 2 spectrum relaxation time and pore throat radius r of the core, and calculating the average pore throat radius of the core through the high-pressure mercury curve Coefficient of variation D r; S4, respectively setting a plurality of different experimental flow rates for each rock core, carrying out a water flooding displacement test in a mode from low flow rate to high flow rate, and recording the recovery ratio eta when the pressure is stabilized at different flow rates, wherein when the recovery ratio of the rock core is not increased after the flow rate is increased, the recovery ratio is the displacement limit of the rock core; S5, constructing displacement characteristic indexes according to t