Rock Permeability Measurement With Sequential Pore Pressure Tests
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Solution Overview
Problem
Existing methods for measuring rock permeability in subsurface reservoirs, particularly at low gas pressures, are inadequate in accounting for the competing effects of compaction and diffusion processes, leading to inaccurate permeability measurements due to the negligible collisions between gas molecules and pore walls.
Innovation Solution
A system and method involving a core sample assembly enclosed in a pressurized container, with large pressure differentials and sequential high and low pore pressure tests, measures permeability by minimizing diffusion effects and capturing compaction impacts, using fluid sensors and pumps to determine permeability based on measured pressures and confining pressures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional steady-state methods with small pressure differentials are used, then measurement precision is improved, but test time increases significantly
Solution Approach 1:
The patent applies parameter changes by using large pressure differentials (e.g., 1000 psi or more) instead of traditional small pressure differentials. This fundamental change in the pressure gradient parameter allows the system to achieve steady-state flow conditions much faster, reducing test time while maintaining measurement precision through the use of multiple test operations at different pressure levels.
2Measurement precision
If low pore pressure tests are performed to capture diffusion effects, then measurement precision is improved, but the complexity of the testing procedure increases
Solution Approach 1:
The patent segments the permeability measurement process into multiple distinct test operations: a low pore pressure test operation to capture diffusion effects, and multiple high pore pressure test operations to capture compaction effects. Each test operation is independently controlled and analyzed, allowing the complex behavior to be broken down into manageable segments that can be processed separately and then integrated.
Solution Approach 2:
The patent employs periodic action by systematically varying the pressure conditions between test operations. The sequence includes a low pore pressure test followed by multiple high pore pressure tests, creating a periodic pattern of stress application and relaxation. This periodic variation allows the system to capture different physical mechanisms (diffusion and compaction) in a structured, repeatable manner.
3Productivity
If large pressure differentials are used, then productivity is improved, but measurement precision may be compromised due to non-linear flow effects
Solution Approach 1:
The patent implements feedback by measuring and monitoring pressure differential values across the core sample during each test operation. The system uses this feedback information to determine when steady-state flow conditions are achieved and to identify optimal test conditions. By continuously monitoring and adjusting based on the measured pressure differentials, the system maintains measurement precision even while using large pressure gradients to improve productivity.
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 test time and provides accurate permeability measurements by accounting for both compaction and diffusion processes, enhancing the prediction of hydrocarbon production by capturing stress-dependent permeability changes.
Implementation Method 1
flowing a pressurized fluid into the pressurized container from the pressurized fluid reservoir
Implementation Method 2
flowing a test fluid into the flow inlet, flowing the test fluid out of the flow outlet
Implementation Method 3
the molecules in the gas flow become subject to diffusion as the collisions among the gas molecules become negligible when the size of the rock pores are close to the same size as the length of the mean free path of the gas molecules
Data Source
AI summary
Systems and methods for measuring rock permeability include positioning a core sample in a core sample assembly that is enclosed in a pressurized container with a flow inlet, a flow outlet, and a pressurized fluid inlet fluidly coupled to a pressurized fluid reservoir that includes a pressurized fluid pump; performing a low pore pressure test operation on the core sample; sequentially performing at least three high pore pressure test operations on the core sample measuring an inlet pressure at the flow inlet, measuring an outlet pressure at the flow outlet, and measuring a confining pressure within the pressurized container; and determining a permeability of the core sample based at least in part on at least one of the measured inlet pressures, at least one of the measured outlet pressures, and at least one of the measured confining pressures.