NMR Diffusion Measurement for Acid Fracturing Optimization
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Solution Overview
Problem
Current methods for acid fracturing and stimulation in hydrocarbon-bearing formations face challenges in efficiently assessing acid diffusivity in real-time during dynamic drilling conditions, which affects the economic efficiency of hydrocarbon extraction.
Innovation Solution
An NMR-based method utilizing gradient fields to measure diffusion coefficients in-situ, with a downhole NMR apparatus and accompanying software that attributes Fourier transforms of spin echoes to spatial distribution of acidity and porosity, and corrects primary diffusion coefficients using a library of corrections validated by independent rotating disk methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If acid injection rate is increased to enhance hydrocarbon extraction efficiency, then productivity increases, but acid consumption increases and acid is depleted too quickly in peripheral regions
Solution Approach 1:
The patent applies preliminary action by using NMR diffusion measurements to assess acid diffusivity before acid injection, allowing optimization of injection parameters in advance. This enables determination of optimal injection rates that maximize productivity while preventing excessive acid consumption and premature depletion in peripheral regions.
Solution Approach 2:
The patent implements feedback by using real-time NMR measurements during acid injection to monitor acid distribution and diffusivity. This feedback loop allows dynamic adjustment of injection rates to maintain optimal productivity while controlling acid consumption and ensuring uniform acid distribution throughout the formation.
2Productivity
If acid concentration is increased to enhance dissolution rate, then etching efficiency improves, but acid penetrates less deeply into the formation
Solution Approach 1:
The patent applies parameter changes by using NMR diffusion measurements to determine the optimal acid concentration that balances etching rate and penetration depth. By measuring acid diffusivity under different concentration conditions, the system identifies the concentration parameter that achieves both sufficient etching efficiency and adequate penetration depth into the formation.
Solution Approach 2:
The patent implements dynamics by enabling real-time adjustment of acid concentration based on NMR measurements of acid distribution and reaction progress. This dynamic adjustment allows the system to optimize the balance between etching rate and penetration depth during the acid injection process, adapting to changing formation conditions.
3Loss of time
If NMR measurements are performed under dynamic drilling conditions, then real-time assessment is enabled, but measurement precision is affected by convective flow and chemical reactions
Solution Approach 1:
The patent applies the intermediary principle by introducing correction factors that mediate between the raw NMR measurements taken under dynamic drilling conditions and the accurate diffusion coefficients. These correction factors account for the effects of convective flow and chemical reactions, allowing real-time assessment while maintaining measurement precision.
Solution Approach 2:
The patent replaces the traditional mechanical approach of performing NMR measurements under static laboratory conditions with an in-situ measurement system that operates under dynamic drilling conditions. By substituting the measurement environment and incorporating computational corrections, the system achieves real-time assessment capability while maintaining accuracy.
Data Source
AI summary
A method for assessing an optimal acid injection rate in the process of hydrocarbon formation stimulation. The method comprises evaluating an anisotropic diffusion coefficient by pulsed gradient NMR, introduction of a semi-empirical correction based on comparison of the downhole conditions with the library of laboratory experiments where such corrections were measured, extrapolation of the library data to the real downhole conditions. The improved values of the diffusion coefficients are applied in determining wormhole regime conditions that are optimal in terms of acid consumption per a unit of stimulated yield of the hydrocarbon.