Permeability Calculation Using NMR Relaxation and Heavy Water Displacement
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Solution Overview
Problem
Current methods for determining permeability in hydrocarbon reservoirs using Nuclear Magnetic Resonance (NMR) face challenges in accurately assessing pore connectivity, especially in carbonate rocks where the correlation between pore body and throat sizes is weak, leading to inaccurate permeability calculations.
Innovation Solution
A method involving the measurement of NMR relaxation times for rock samples saturated with regular water and heavy water, followed by calculation of a pore connectivity factor based on volume displacements, which is then used to determine permeability using a modified permeability model that incorporates the connectivity factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional NMR methods are used to determine permeability, then the measurement process is simple, but the accuracy of permeability calculation is poor due to weak correlation between pore body and throat sizes in carbonate rocks
Solution Approach 1:
The patent changes the physical state of water from regular water to heavy water (deuterium oxide) to alter the NMR relaxation characteristics. This parameter change enables differentiation between pore body and pore throat contributions, allowing accurate permeability calculation in carbonate rocks where conventional methods fail due to weak pore body-throat correlation
Solution Approach 2:
Heavy water acts as an intermediary substance that mediates between the NMR measurement process and the pore structure characterization. By using heavy water instead of regular water, the patent creates a measurable signal difference that serves as an intermediary to extract accurate pore connectivity and permeability information
2Measurement precision
If NMR relaxation times are measured for both regular water and heavy water saturated samples, then pore connectivity can be accurately assessed, but the measurement time and procedure complexity increase
Solution Approach 1:
The patent performs preliminary saturation of the rock sample with heavy water before conducting the NMR measurements. This preliminary action ensures that the heavy water is uniformly distributed in the pore structure, enabling accurate pore connectivity assessment while streamlining the subsequent measurement process
Solution Approach 2:
By changing the water type parameter from regular water to heavy water, the patent creates distinct NMR relaxation time signatures that enable accurate pore connectivity assessment. The parameter change provides sufficient signal differentiation to achieve accurate measurements without requiring excessively long measurement durations
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 more accurate permeability assessments, improving the accuracy of reservoir estimation and hydrocarbon production forecasting, and is applicable to both homogeneous and inhomogeneous pore systems.
Implementation Method 1
measuring a first set of Nuclear Magnetic Resonance (NMR) relaxation times for the rock sample saturated with regular water (H 2 O)
Implementation Method 2
injecting heavy water (D 2 O) into the rock sample; measuring a second set of NMR relaxation times for the rock sample after injecting D 2 O; calculating a pore connectivity factor based on a ratio between a first volume displacement of a first pore system and a second volume displacement of a second pore system
Data Source
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AI summary
The present disclosure describes methods and systems, including computer-implemented methods, computer program products, and computer systems, for determining a permeability of a rock sample. One method includes measuring a first set of Nuclear Magnetic Resonance (NMR) relaxation times for the rock sample saturated with regular water (H2O); injecting heavy water (D2O) into the rock sample; measuring a second set of NMR relaxation times for the rock sample after injecting D2O; calculating a pore connectivity factor based on the first set of NMR relaxation times and the second set of NMR relaxation times; and calculating the permeability of the rock sample based on the pore connectivity factor.