NMR Pore Size Distribution Correction for Rough Rock Surfaces
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Solution Overview
Problem
Current methods for determining pore size distribution in rocks with rough surfaces, such as those used in hydrocarbon reservoirs, face inaccuracies due to large pores with rough surfaces, which introduce errors in capillary pressure measurements and NMR methods.
Innovation Solution
The method involves saturating a rock sample with a fluid, acquiring initial NMR measurements, applying an external force to expel fluid from larger pores, and then acquiring subsequent NMR measurements to identify and exclude T2 contributions from fluid films on rough surfaces, allowing for accurate determination of pore size distribution by comparing T2 distributions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional capillary pressure methods are used to measure pore size distribution, then the measurement process is simple, but large pores with rough surfaces introduce errors and reduce measurement precision
Solution Approach 1:
The patent segments the pore population into two distinct groups: larger pores with rough surfaces and smaller pores with smoother surfaces. This segmentation allows the measurement method to differentiate and treat each pore type separately, preventing the rough surface pores from contaminating the measurements of smooth surface pores, thereby resolving the measurement precision issue without requiring complex additional equipment
Solution Approach 2:
The patent extracts or removes the contribution of fluid films from rough surface pores from the overall NMR signal. By applying external force to expel fluid from larger pores and then identifying and excluding the T2 contributions corresponding to fluid remaining on interior surfaces of these pores, the method isolates the signal from smaller pores with smoother surfaces, improving measurement accuracy without adding device complexity
2Measurement precision
If NMR measurements are taken without excluding fluid films on rough surfaces, then the measurement process is straightforward, but the pore size distribution data becomes inaccurate
Solution Approach 1:
The patent performs preliminary action by first saturating the rock sample with fluid and then applying external force to expel fluid from larger pores before taking the final NMR measurements. This preliminary expulsion step ensures that when the NMR measurements are taken, the fluid films on rough surfaces of larger pores are minimized or removed, preventing them from interfering with the accurate measurement of pore size distribution in smaller pores
Solution Approach 2:
The patent extracts the unwanted signal component by identifying and excluding the portion of the T2 distribution that corresponds to fluid remaining on interior surfaces of larger pores with rough surfaces. This extraction process removes the harmful signal contribution from rough surface fluid films while preserving the accurate signal from smaller pores, thereby improving measurement precision
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 corrects inaccuracies in pore size distribution measurements by accounting for fluid films on rough surfaces, providing more accurate capillary pressure curves and pore size distributions, thus improving the accuracy of hydrocarbon reservoir analysis.
Implementation Method 1
acquiring a first set of nuclear magnetic resonance (NMR) measurements of the rock sample
Implementation Method 2
applying, subsequent to acquiring the first set of NMR measurements, a first external force to the rock sample to expel the fluid from a first plurality of pores of the rock sample
Data Source
AI summary
A method for determining pore size distribution of rocks is provided. Capillary pressure measurements on rock cores are analyzed to determine a pore size distribution, with smaller pores requiring greater capillary pressure to relinquish contained fluid. Large pores with rough surfaces introduce inaccuracies in determining the pore size distribution. Embodiments of the invention correct the rough surface induced inaccuracies by measuring the shift in NMR T2 distribution from full saturation to the current state of desaturation and subtracting the T2 contributions in the desaturated state that have smaller T2 values (i.e., smaller transverse relaxation time) than the smallest T2 values (i.e., shortest transverse relaxation time) in the saturated distribution.