CN-122014182-A - Polymer flooding injection concentration determining method based on oil phase fluidity control

CN122014182ACN 122014182 ACN122014182 ACN 122014182ACN-122014182-A

Abstract

The invention relates to a polymer flooding injection concentration determination method based on oil phase fluidity control, which comprises the steps of determining the minimum effective viscosity of an underground polymer solution required by meeting the fluidity control requirement based on an oil phase fluidity control criterion, estimating the front edge concentration of a polymer slug when the polymer slug moves to the front edge in a stratum, verifying and compensating stratum shearing loss to the current ground injection concentration to obtain the zero shear viscosity of a well bottom, determining the ground zero shear viscosity of ground injection liquid, reversely solving the corresponding polymer concentration to obtain the ground minimum injection concentration, updating the ground injection concentration and a permeability coefficient, and carrying out iterative calculation until the difference between the ground minimum injection concentrations obtained by two adjacent iterations is smaller than a preset tolerance. The closed loop iteration coupling multi-loss mechanism ensures self-consistency of parameters, improves concentration design precision and provides more scientific engineering basis for polymer flooding in a high water content period.

Inventors

WANG FUYONG
ZHU WEIYAO

Assignees

北京科技大学

Dates

Publication Date: 20260512
Application Date: 20260127

Claims (10)

1. A polymer flooding injection concentration determination method based on oil phase fluidity control, the method comprising: Determining minimum effective viscosity of the underground polymer solution required to meet the mobility control requirement based on the oil phase mobility control criterion according to the permeability reduction coefficient and the basic oil reservoir parameter; estimating the front edge concentration of the polymer slug when the polymer slug moves to the front edge in the stratum according to the ground injection concentration, the basic oil reservoir parameter and the polymer system parameter; Verifying and compensating the stratum shear loss of the current ground injection concentration according to the minimum effective viscosity, the basic oil reservoir parameter, the polymer system parameter and the engineering operation parameter so as to determine the available zero shear viscosity of the bottom of the well; According to the zero shear viscosity of the bottom hole and the engineering operation parameters, determining the zero shear viscosity of the ground, which is required to be possessed by the ground injection liquid; reversely solving the corresponding polymer concentration according to the ground zero shear viscosity and the polymer system parameter to obtain the ground minimum injection concentration; Taking the ground minimum injection concentration obtained in the iteration as the ground injection concentration of the next iteration, updating the permeability coefficient according to the newly estimated front edge concentration, repeatedly executing the steps to perform the next iteration calculation until the difference between the ground minimum injection concentrations obtained in two adjacent iterations is smaller than a preset tolerance, and outputting the final minimum ground injection concentration.
2. The method for determining polymer flooding injection concentration based on oil phase fluidity control of claim 1, wherein the basic reservoir parameters include crude oil viscosity, current water saturation, and oil-water relative permeability curve; Determining a minimum effective viscosity of the subterranean polymer solution required to meet the mobility control requirements based on the oil phase mobility control criteria based on the permeability reduction coefficient and the base reservoir parameters, comprising: according to the oil-water relative permeability curve, calculating the oil phase relative permeability and the water phase relative permeability corresponding to the current water saturation; and determining the minimum effective viscosity based on an oil phase fluidity control criterion according to an initial preset or updated permeability reduction coefficient, the oil phase relative permeability, the water phase relative permeability and the crude oil viscosity.
3. The method for determining the injection concentration of the polymer flooding based on the oil phase fluidity control according to claim 2, wherein the calculation formula of the minimum effective viscosity is: , Wherein S w is the current water saturation of the target oil reservoir, k ro (S w ) and k rw (S w ) are the oil phase relative permeability and the water phase relative permeability corresponding to the current water saturation, mu o is the crude oil viscosity, and R k is the permeability reduction coefficient.
4. The method for determining polymer flooding injection concentration based on oil phase fluidity control of claim 1, wherein the basic reservoir parameters include rock density and porosity, and the polymer system parameters include maximum adsorption amount and adsorption equilibrium coefficient; Estimating a leading edge concentration of the polymer slug as it migrates to the leading edge in the formation based on the surface injection concentration, the base reservoir parameter, and the polymer system parameter, comprising: establishing a system of equations between the ground injection concentration, the front edge concentration and the amount of polymer loss caused by adsorption based on a mass balance principle according to an initial preset or updated ground injection concentration, the maximum adsorption amount, the adsorption balance coefficient, the rock density and the porosity; and solving the equation set to obtain the front edge concentration.
5. The method for determining polymer flooding injection concentration based on oil phase fluidity control of claim 4, wherein the system of equations is: , wherein C p,inj is the surface injection concentration, C p,front is the front concentration, ρ rock is the rock density, For the porosity, a is the maximum adsorption quantity, b is the adsorption equilibrium coefficient, PV is the pore volume, For the average amount of adsorption, the amount of adsorption, M rock is the rock mass, which is the average concentration of polymer.
6. The method of determining polymer flooding injection concentration based on oil phase mobility control of claim 1, wherein verifying and compensating for formation shear losses for current surface injection concentration based on the minimum effective viscosity, the base reservoir parameters, the polymer system parameters, and engineering operating parameters to determine available downhole zero shear viscosity comprises: Calculating stratum equivalent shear rate according to the basic oil reservoir parameters and the engineering operation parameters; according to the minimum effective viscosity, the stratum equivalent shear rate and the polymer system parameters, a shear thinning model is utilized to reversely push the zero shear viscosity required for meeting the minimum effective viscosity requirement, so that the required zero shear viscosity is obtained; Obtaining actual zero shear viscosity according to the current ground injection concentration and a zero shear viscosity function in the polymer system parameters; Judging whether the actual zero shear viscosity is higher than the required zero shear viscosity: if yes, taking the actual zero shear viscosity as the bottom hole zero shear viscosity; if not, the ground injection concentration is adjusted until the judging condition is met.
7. The method for determining polymer flooding injection concentration based on oil phase mobility control according to claim 6, wherein the basic reservoir parameters comprise absolute permeability, porosity, current oil saturation, and oil-water relative permeability curve, and the engineering operation parameters comprise oil phase darcy speed and formation geometry factor characterizing pore structure complexity; the calculation formula of the stratum equivalent shear rate is as follows: , Wherein beta is the stratum geometry factor representing the complexity of the pore structure, v o is the Darcy speed of the oil phase, K is the absolute permeability, In order to achieve this porosity, the porous body, For the current saturation level of oil content, The relative permeability of the oil phase corresponding to the current oil saturation.
8. The method for determining polymer flooding injection concentration based on oil phase fluidity control of claim 7, wherein the polymer system parameters include infinite shear viscosity, characteristic shear rate, and power law index; the calculation formula of the required zero shear viscosity is as follows: , Wherein mu eff,req is the minimum effective viscosity mu ∞ is the infinite shear viscosity, For the characteristic shear rate, p is the power law exponent.
9. The method for determining polymer flooding injection concentration based on oil phase fluidity control of claim 1, wherein the engineering operation parameters include borehole shear viscosity retention; the calculation formula of the ground zero shear viscosity is as follows: , Wherein μ 0 (C p,inj ) is the bottom hole zero shear viscosity, η perf is the borehole shear viscosity retention rate.
10. The method for determining the injection concentration of the polymer flooding based on the oil phase fluidity control according to claim 1, wherein the polymer system parameters comprise a viscosity-concentration standard curve or a fitting formula of a polymer solution, and the expression is as follows: , Wherein mu w is the viscosity of injected water, A 1 、A 2 、A 3 and s are fitting coefficients, and C sep is an electrolyte concentration correction factor; Reversely solving the corresponding polymer concentration according to the ground zero shear viscosity and the polymer system parameter to obtain the ground minimum injection concentration, and making the polymer in the formula And for the zero shear viscosity of the ground, the minimum polymer concentration C p which is obtained by solving the equation and meets the viscosity requirement is the minimum injection concentration of the ground.

Description

Polymer flooding injection concentration determining method based on oil phase fluidity control Technical Field The invention relates to the technical field of petroleum and natural gas exploitation, in particular to a polymer flooding injection concentration determination method based on oil phase fluidity control. Background In the middle and later stages of oil field development, the water content of the stratum is continuously increased, the effect of conventional water injection development is gradually deteriorated, and the improvement of the recovery ratio is faced with a bottleneck. Polymer flooding is used as a mature chemical flooding technology, and high molecular polymers (such as partially Hydrolyzed Polyacrylamide (HPAM)) are added into injected water to improve the viscosity of the displacement fluid and the water-oil fluidity ratio, so that the sweep range is enlarged, and the water burst and viscous propulsion phenomena are inhibited. The technology has become an important means for further improving the recovery ratio of the high-water-content oil field. In polymer flooding scheme design, determination of injection concentration directly affects technical effects and economic benefits. Too low a concentration can not effectively control fluidity, which easily results in unstable displacement process and fingering, and too high a concentration can significantly increase cost and may damage the formation or degrade the polymer due to too high injection pressure. Therefore, how to scientifically determine the minimum necessary polymer injection concentration on the premise of ensuring the displacement effect is the key for optimizing the design and implementation of the polymer flooding. Currently, the concentration determination commonly employed in polymer flooding design is based on the "total fluidity control criteria". This criterion requires that the fluidity of the polymer solution is not greater than the minimum of the total fluidity of the oil-water phases at its leading edge, expressed generally as: , Wherein, K is absolute permeability, K rw、kro is relative permeability of water phase and oil phase respectively, mu w、μo is viscosity of water and crude oil respectively, mu p is effective viscosity of polymer solution, and R k is permeability reduction coefficient caused by polymer adsorption. The criteria is intended to maintain stability of the macroscopic displacement front by controlling the overall migration velocity of the polymer slugs not to exceed the velocity of the forward oil-water mixing zone. The method is characterized in that the method comprises the steps of (1) taking the total fluidity of a polymer slug with the fluidity not larger than that of a front oil-water mixing belt of the polymer slug as a standard, wherein in a high water saturation area, the water phase fluidity is dominant in the total fluidity, the method can ensure that the polymer slug is not advanced in a macroscopic manner than the oil-water mixing belt, but the viscosity index of the residual crude oil on a microscopic scale cannot be restrained, so that the crude oil is bypassed and the displacement efficiency is reduced, and (2) the method is used for widening the limitation of the polymer due to the inclusion of the water phase fluidity, the minimum injection concentration designed according to the method possibly does not realize the optimal value for stable displacement, the high polymer consumption and the insufficient pertinence are easily caused, or otherwise, the viscosity of the polymer solution is caused due to the insufficient concentration, so that the technical and economic effects are affected, and (3) when key parameters such as shear are calculated, the actual degradation process of the polymer solution in the flowing environment of an oil phase is not fully considered, so that the accuracy of the prediction of loss is caused, and the accuracy of the ground injection parameters is affected from underground demand. In general, in areas of high water saturation, the overall oil-water flow is dominated by the water-phase flow, where the local flow in the oil-bearing pores may be much higher than the flow of the crude oil itself, even though the overall polymer flow satisfies the inequality described above. The polymer solution can cause viscous fingering to crude oil in microscopic pore canals, so that the crude oil is bypassed and cannot be effectively driven out, thereby reducing microscopic oil displacement efficiency and affecting final recovery ratio. That is, while the above criteria may constrain the advancement of the polymer as a whole, it is not possible to effectively limit the advancement rate of the polymer relative to the crude oil on the pore scale, and thus it is difficult to achieve truly protective displacement of the oil phase. Disclosure of Invention In order to solve the technical problem of insufficient micro fingering control of polymer flooding in the prior ar