Matrix Permeability Measurement Using Transient Pressure Decay
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Solution Overview
Problem
Measuring matrix permeability of subsurface formations is challenging due to the presence of induced fractures and microfractures, which can lead to inaccurate permeability measurements, especially in unconventional rocks with low permeability and heterogeneous textures.
Innovation Solution
A method and system for determining matrix permeability by positioning a subsurface formation sample in a measurement cell, flowing a fluid through it, and measuring pressure changes before the upstream and downstream pressures merge, using data arrays G(t) and f(t) to calculate permeability based on pressure data and volume ratios, while applying effective stress pressure and confining pressure to minimize the effect of induced fractures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional permeability measurement methods are used on rock samples retrieved to the earth surface, then the measurement process is simple, but the presence of induced fractures and microfractures causes inaccurate permeability measurements
Solution Approach 1:
The patent applies parameter changes by measuring permeability at different pressure conditions (in situ pressure vs. atmospheric pressure) and different rates (steady-state vs. transient flow). By changing these parameters, the measurement can distinguish between matrix permeability and fracture permeability, resolving the accuracy issue without requiring complex equipment - just modified measurement protocols.
Solution Approach 2:
The patent segments the permeability measurement into distinct components: matrix permeability measurement and fracture permeability measurement. By separating these two measurement objectives and using different measurement conditions for each, the system can accurately determine matrix permeability while accounting for the presence of fractures, improving precision without proportionally increasing device complexity.
2Measurement precision
If rock samples are retrieved to the earth surface for measurement, then the measurement can be performed in a laboratory setting, but induced fractures are generated that artificially increase permeability
Solution Approach 1:
The patent applies preliminary action by performing permeability measurements in the lab while the rock sample still retains its in situ pressure conditions or by systematically applying pressure conditions that replicate the subsurface environment. This preliminary measurement approach allows characterization of matrix permeability before the induced fractures can contaminate the results, improving both precision and reliability.
Solution Approach 2:
The patent converts the harmful effect of induced fractures into a beneficial measurement opportunity by using the fracture response to pressure changes as a diagnostic tool. By measuring permeability at different pressure conditions, the induced fractures provide a signal that can be separated from the matrix permeability signal, allowing accurate matrix permeability determination while utilizing the fracture information for additional characterization.
3Measurement precision
If steady-state flow measurement is used, then the measurement is straightforward, but it cannot distinguish between matrix permeability and fracture permeability
Solution Approach 1:
The patent applies periodic action by using transient flow measurements where pressure is changed over time (e.g., pressure pulse decay tests). This time-dependent approach creates distinct flow patterns that can be analyzed to separate matrix permeability from fracture permeability. The periodic pressure changes allow the system to observe how fluid moves through different pathways at different rates, improving precision without significantly reducing measurement efficiency.
Solution Approach 2:
The patent transitions from static steady-state measurement to dynamic transient measurement. By applying time-varying pressure conditions and analyzing the dynamic response of the rock sample, the system can distinguish between the rapid flow through fractures and the slower flow through the matrix. This dynamic approach improves measurement precision while maintaining reasonable productivity through efficient data collection protocols.
4Measurement precision
If pressure merge point is used to determine permeability, then the measurement captures total permeability, but it includes the effect of induced fractures that mask matrix permeability
Solution Approach 1:
The patent applies partial action by measuring permeability under specific pressure conditions that selectively highlight matrix flow rather than total flow. By using pressure conditions where the pressure gradient is sufficient to drive flow through the matrix but where fracture flow can be differentiated or excluded from the measurement interpretation, the system obtains accurate matrix permeability data without requiring excessively long measurement times to wait for complete pressure equilibrium.
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 provides quicker, higher sensitivity, and higher accuracy in measuring matrix permeability, reducing the impact of induced microcracks and heterogeneity, and allowing for the determination of both matrix and fracture permeability in the same measurement, improving the representation of rock permeability distributions.
Implementation Method 1
flowing a fluid through the sample from the upstream reservoir to the downstream reservoir, measuring changes of an upstream pressure associated with the upstream reservoir and a downstream pressure associated with the downstream reservoir
Implementation Method 2
measuring changes of an upstream pressure associated with the upstream reservoir and a downstream pressure associated with the downstream reservoir in a measurement time period
Data Source
AI summary
Systems, methods, and apparatus for determining permeability of subsurface formations are provided. In one aspect, a method includes: positioning a sample of the subsurface formation in a measurement cell, fluidly connecting an inlet and an outlet of the sample to an upstream reservoir and a downstream reservoir, respectively, flowing a fluid through the sample from the upstream reservoir to the downstream reservoir, measuring changes of an upstream pressure associated with the upstream reservoir and a downstream pressure associated with the downstream reservoir in a measurement time period, and determining a matrix permeability of the subsurface formation based on measurement data before the upstream pressure and the downstream pressure merge at a merging time point.