A method for calculating critical injection pressure of fluid in a nanopore throat

Abstract

The invention discloses a method for calculating critical injection pressure of fluid in a nanopore throat. The method comprises the following steps: 1) constructing a nanopore throat structure; 2) constructing a fluid and a push plate; 3) adjusting the size of the model, setting a vacuum area, and finishing model construction; 4) distributing force field and charge parameters; and 5) carrying outmolecular mechanics optimization, balanced molecular dynamics simulation and tensile molecular dynamics simulation, counting and analyzing the stress change process of the oil phase in the nanopore throat filling process, and obtaining the critical injection pressure of the oil phase in the nanopore throat filling process through a formula P = F / S. According to the invention, a computer simulation technology is utilized to obtain the calculation method of the critical injection pressure of the fluid in the nanopore throat; the result deviation caused by ignoring the intermolecular interactionin the mathematical calculation method is avoided, the method can realize the regulation and control of the simulation conditions such as the nanopore throat size and the fluid components, and a convenient and effective way is provided for the research of the critical physical properties of the unconventional oil and gas reservoir.

Description

technical field [0001] The invention belongs to the technical field of molecular simulation, in particular to a method for calculating the critical injection pressure of a fluid in a nanopore throat. Background technique [0002] Unconventional oil and gas reservoirs are characterized by tight lithology, low porosity, low permeability and low natural productivity. Studies in recent years have found that the matrix of unconventional oil and gas reservoirs is dominated by nanoscale pore-throat network systems, and the pore-throat diameters are distributed in the range of several nanometers to hundreds of nanometers. figure 1 . At the nanometer scale, the influence of fine pore throats is enhanced, the specific surface area increases, and there is a strong interface effect between the fluid and the rock, and the introduction of the interface effect leads to the generation of injection pressure. Reservoir theoretical analysis and exploration practice show that unconventional o...

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Problems solved by technology

[0003] The study of critical injection pressure is a delicate and arduous task. Various methods currently used have their own advantages and disadvantages, for example: (1) Mathematical calculation method, some scholars calculate injection pressure according to the physical parameters of fluid and rock, while critical injection pressure Pressure is the result of the interaction between fluid and rock, and the mathematical model used to calculate injection pressure regards fluid and solid as continuous phases, thus ignoring the intermolecular interaction; therefore, the calculation results of mathematical methods are often inconsistent with reality, and are not practical. powerful

(2) Numerical simulation method. Numerical simulation of oil and gas reservoirs is a numerical calculation method that uses computers to study fluid seepage laws in oil and gas reservoirs. This method is simple, convenient and has a short cycle. However, the critical injection can only be calculated if the pore-throat distribution curve and actual production data are accurately obtained. pressure; therefore, this method has certain limitations

(3) Experimental method. Many scholars have studied the critical injection pressure of tight rocks. At present, the physical simulation of crude oil filling is widely used, that is, the pressure difference-flow method. This experimental method is simple and intuitive, and it is widely used, but still There are disadvantages such as difficult core preparation, long test period and difficult capture of injection pressure

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