Tight-Reservoir Oil–Gas Relative Permeability Testing With 1D Simulation
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Solution Overview
Problem
Existing methods for determining oil and gas relative permeability in low-permeability or tight reservoirs face challenges such as difficulty in simultaneous two-phase fluid injection, long test cycles, and inaccuracies due to high pressure gradients and neglect of gas compressibility and mass transfer, leading to significant deviations from actual permeability values.
Innovation Solution
A method using a relative permeability testing device with a piston container, pressure gauges, and a one-dimensional numerical simulation grid model to simulate reservoir performance, adjusting permeability curves to minimize pressure differences and improve accuracy, incorporating a confining pressure pump, oil and gas separator, and balance to measure and simulate permeability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the steady-state method is used for low-permeability or tight reservoirs, then the measurement can be performed, but it is difficult to inject two-phase fluid simultaneously and the test cycle is long
Solution Approach 1:
The patent replaces the traditional mechanical steady-state injection system with a numerical simulation system. Instead of physically injecting two-phase fluids through complex mechanical control, the invention uses numerical models to simulate fluid flow and calculate relative permeability, thereby eliminating the long test cycle and injection difficulty while maintaining measurement accuracy.
Solution Approach 2:
The patent creates a numerical copy of the reservoir system through a one-dimensional numerical simulation grid model. This virtual model replicates the physical reservoir's behavior under various conditions, allowing relative permeability to be determined through simulation rather than lengthy physical experimentation, thus resolving the contradiction between measurement feasibility and test duration.
2Productivity
If the unsteady-state method is used, then the test time is reduced, but the pressure gradient is significantly higher than actual reservoir conditions leading to large differences in measured permeability
Solution Approach 1:
The patent changes the key parameter of pressure gradient from high (unsteady-state) or variable (steady-state) to a controlled range that matches actual reservoir conditions. The numerical simulation allows the pressure gradient to be set within 0.001-0.1 MPa/m, replicating real reservoir conditions and eliminating the accuracy error caused by excessive pressure gradients while maintaining the speed advantage of unsteady-state methods.
Solution Approach 2:
The patent introduces a numerical simulation model as an intermediary between the physical experiment and the actual reservoir. This model acts as a bridge that translates rapid unsteady-state test data into accurate relative permeability values by applying reservoir-matching pressure gradients, thus resolving the contradiction between fast testing and accurate measurement.
3Productivity
If the JBN method is used to calculate relative permeability, then the calculation can be performed quickly, but it does not consider gas compressibility, mass transfer, and fluid property changes leading to significant deviation from actual values
Solution Approach 1:
The patent transitions from the static JBN calculation method to a dynamic numerical simulation approach. The simulation dynamically accounts for gas compressibility, mass transfer between phases, and fluid property changes throughout the test process. This dynamic modeling maintains computational efficiency while dramatically improving accuracy by capturing the evolving physical conditions that the static JBN method overlooks.
Solution Approach 2:
The patent performs preliminary setup of the numerical simulation model with all relevant physical parameters (gas compressibility, mass transfer coefficients, fluid properties) before running the test. This preliminary configuration ensures that all critical factors are built into the calculation framework from the start, allowing rapid computation that includes complex physical effects without sacrificing speed, unlike the oversimplified JBN method.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method reduces measurement time and cost while enhancing the accuracy of oil and gas relative permeability determination in tight reservoirs by aligning simulation results with experimental data, addressing the limitations of prior art.
Implementation Method 1
The confining pressure pump is configured to provide a confining pressure for the core holder
Implementation Method 2
The relative permeability testing device further includes a confining pressure pump, an oil and gas separator, a gas flowmeter and a balance
Data Source
AI summary
The present disclosure relates to a method for determining oil and gas relative permeabilities of a reservoir. The method includes: drilling a cylindrical core from a to-be-tested reservoir; injecting an oil and gas mixture into the cylindrical core through the piston container at a set flow rate by using the relative permeability testing device, and reducing pressures at a control end of the back pressure valve in sequence to obtain experimental values acquired under each pressure at the control end of the back pressure valve; equivalently simulating developing performance of a producing well of the to-be-tested reservoir using a one-dimensional numerical simulation grid model based on current oil and gas phase relative permeability curves, so as to obtain simulation values at different times; constructing an objective function according to the experimental and simulation values; determining whether a value of the objective function reaches a preset target value.