Shale Gas Permeability Measurement via Transient Pulse Decay
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Solution Overview
Problem
Current methods for determining pressure-dependent shale gas permeability in shale formations are inefficient, requiring multiple laboratory tests and suffering from non-uniqueness in parameter estimation and lack of practical techniques for routine measurement.
Innovation Solution
A new analytical solution for one-dimensional gas flow is developed, allowing for direct measurement of shale gas permeability and porosity using a single test run without presuming the form of the parametric relationship between permeability and pressure, through a method involving a pressure vessel, gas transport parameter calculation, and porosity determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple pulse-decay permeability tests under different gas pressures are performed to determine pressure-dependent shale gas permeability, then measurement accuracy is improved, but time consumption increases significantly due to the need to equilibrate the test system from one test pressure to the next
Solution Approach 1:
The patent combines multiple pressure-dependent permeability measurements into a single continuous transient flow test. By applying a step change in gas pressure and monitoring the transient pressure response, the method simultaneously determines permeability at multiple pressure conditions without requiring separate equilibrium tests, thus eliminating the time-consuming pressure equilibration steps between tests.
Solution Approach 2:
The patent transitions from static equilibrium measurements to dynamic transient flow measurements. Instead of performing separate tests at each pressure condition, the method captures the dynamic pressure response during a single transient flow event, allowing permeability to be determined as a function of pressure throughout the transient process, thereby reducing total measurement time.
2Adaptability or versatility
If numerical modeling with parameter estimation is used to determine gas permeability as a function of pressure, then flexibility in incorporating pulse disturbance is improved, but non-uniqueness of parameter estimation problems arises
Solution Approach 1:
The patent employs a feedback approach where the measured transient pressure response is directly used to calculate permeability at each pressure condition through the analytical solution. This eliminates the iterative parameter estimation process in numerical modeling that leads to non-uniqueness, providing a direct and unique determination of pressure-dependent permeability from the measured data.
Solution Approach 2:
The patent replaces the complex numerical modeling and iterative parameter estimation mechanical process with an analytical solution based on fundamental flow equations. This substitution provides a direct calculation method that avoids the non-uniqueness issues inherent in numerical inverse modeling while maintaining the ability to account for pulse disturbance effects.
3Adaptability or versatility
If a formulation of gas permeability as a function of gas pressure is developed and parameters are estimated by numerically matching test results, then ability to handle larger pressure pulses is improved, but accuracy is limited by the quality of the permeability formulation
Solution Approach 1:
The patent inverts the conventional approach by not starting with a predefined permeability formulation and estimating its parameters. Instead, it directly calculates permeability as a function of pressure from the measured transient response using an analytical solution, allowing the data to speak for itself without being constrained by the quality or assumptions of a pre-established formulation.
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
This approach enables efficient estimation of permeability and porosity from a single test run, improving the accuracy and efficiency of pressure-dependent gas permeability measurement in shale formations.
Implementation Method 1
In these nano pores, a non-negligible portion of gas molecules collides more often with the pore wall than with other molecules, and thus so-called 'slip flow' and Knudsen diffusion occur.
Implementation Method 2
In these nano pores, a non-negligible portion of gas molecules collides more often with the pore wall than with other molecules, and thus so-called 'slip flow' and Knudsen diffusion occur.
Implementation Method 3
Initially, the system is in equilibrium with a given gas pressure. A small pressure pulse is then introduced into the upstream gas reservoir, such that the pulse does not have a significant disturbance to the gas pressure in the system. The pressures at the two gas reservoirs are monitored as a function of time.
Data Source
AI summary
Methods and systems for determining permeability, as a function of pore pressure, and porosity of a subsurface formation. The method includes positioning a sample in a sample assembly comprising of a gas and a pressure gauge, inside a pressure vessel comprising gas or liquid and a pressure gauge, measuring a first gas pressure, pi, of the sample inside the pressure vessel, applying a second gas pressure, po, to the pressure vessel, the second gas pressure being greater than the first gas pressure, measuring a third gas pressure, p, at time, t, at location, x, from the inlet of sample inside the pressure vessel, determining a total gas mass per unit volume of the subsurface formation, m, and determining the permeability, k, of the subsurface formation as a function of pore pressure based at least in part on the first gas pressure, the second pressure, the third gas pressure, and the gas density, with a single test run.