NMR Relaxation Time Cutoff Estimation via Numerical Simulation
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Solution Overview
Problem
Current methods for determining nuclear magnetic resonance relaxation time cutoffs for bound-water and free-fluid indices in rock require time-consuming and inconsistent core analysis protocols, involving NMR measurements on core plugs under irreducible water saturation.
Innovation Solution
A system and method that use computer processors to determine relaxation time cutoffs by analyzing measured values of permeability, wettability, and porosity from core plugs, predicting model parameters to fit permeability and wettability predictions, and identifying an optimal cutoff value without requiring NMR measurements on core plugs for both saturated and dry conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional core analysis protocol with NMR measurements under irreducible water saturation is used, then measurement precision of relaxation time cutoff is improved, but loss of time and productivity deteriorate
Solution Approach 1:
The patent creates a virtual model that replicates the complex physical core analysis process through numerical simulations. Instead of performing actual NMR measurements on physical core plugs under irreducible water saturation, the system uses numerical models to simulate the NMR response and determine relaxation time cutoffs, achieving comparable accuracy without the time-consuming physical experiments
Solution Approach 2:
The patent performs preliminary numerical simulations to establish the relationship between NMR parameters and rock properties before actual field measurements. By pre-calculating the expected NMR responses for different relaxation time cutoffs using numerical models, the system prepares reference data that accelerates the subsequent determination process while maintaining measurement precision
2Reliability
If traditional core analysis protocol is used, then reliability of relaxation time cutoff calibration is improved, but device complexity and ease of operation worsen
Solution Approach 1:
The patent replaces the complex mechanical and experimental system of physical core analysis with a computational system. Instead of using NMR spectrometers, centrifuges, and manual measurement procedures, the invention uses numerical simulations and computer-based algorithms to determine relaxation time cutoffs, simplifying the overall system while maintaining reliability through validated mathematical models
Solution Approach 2:
The patent develops a universal numerical model that can determine relaxation time cutoffs for different rock types and NMR conditions through a single integrated approach. The numerical simulation framework is designed to handle various scenarios (different porosity, permeability, fluid saturation) without requiring separate specialized procedures for each case, thereby improving consistency while reducing protocol complexity
3Measurement precision
If NMR measurements under full saturation and irreducible water saturation are performed, then measurement precision of bound-water and free-fluid indices is improved, but loss of time and productivity worsen
Solution Approach 1:
The patent uses numerical simulations to replicate the NMR measurement process and extract bound-water and free-fluid indices without performing actual dual-condition NMR measurements. The numerical model calculates the expected NMR signals for bound and free fluids based on rock properties and relaxation time distributions, providing accurate index determination while eliminating the need for time-consuming physical measurements under both full saturation and irreducible water saturation conditions
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 significantly reduces the time and cost associated with determining relaxation time cutoffs, providing a more consistent and efficient method for analyzing nuclear magnetic resonance data, while maintaining accuracy in interpreting well log data.
Implementation Method 1
Nuclear magnetic resonance (NMR) well logs are commonly used to interpret rock pore size and provide essential information for petrophysical evaluation. For a porous rock of porosity φ and hydraulic permeability k, the time-domain spin echo trains M(t) measured by the NMR antenna
Implementation Method 2
Assuming the pore space is saturated with light liquids whose bulk relaxation times are in the order of or more than 1000 ms, the overall T2 relaxation of fluids in pores is dominated by the surface relaxation mechanism: larger values of T2 correspond to larger pores
Data Source
AI summary
A nuclear magnetic resonance relaxation time cutoff between results for a bound-water index of rock and a free-fluid index of the rock is determined. The determination is made based on measured and predicted values for permeability and/or wettability over a set of core plugs. The determination does not require a nuclear magnetic resonance operation performed on the core plugs under irreducible water saturation.