NMR Water Cut Measurement Using Diffusion Gradient Segmentation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current methods for determining the water cut in hydrocarbon reservoirs using 2D T1/T2 NMR measurements face ambiguity in distinguishing between water and oil due to similar T1 and T2 distributions, leading to inaccurate predictions.
Innovation Solution
Conducting a standard T1/T2 experiment twice, once without and once with a field gradient, to differentiate between water and oil by shifting cross peaks representing water to lower T2 values, while those representing oil remain unchanged, thereby resolving ambiguity in assignments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If 2D T1/T2 NMR measurements are used to determine water cut, then measurement capability is provided, but ambiguity in distinguishing water and oil occurs due to similar T1 and T2 distributions
Solution Approach 1:
The patent transitions from 2D T1/T2 relaxation measurements to 3D T1/T2/D (diffusion) measurements by incorporating a third dimension of diffusion coefficient. This additional dimension provides new information that distinguishes water from oil, as they have different diffusion coefficients, thereby resolving the ambiguity that exists in 2D space where T1 and T2 distributions overlap.
Solution Approach 2:
The patent changes the measurement parameters by adding diffusion coefficient (D) as a new parameter to the existing T1 and T2 relaxation times. This parameter change enables better differentiation between water and oil phases, as water and oil have distinctly different diffusion coefficients, thus improving measurement precision while reducing ambiguity.
2Ease of operation
If standard T1/T2 experiment is conducted without field gradient, then measurement simplicity is maintained, but diffusion influence on water cannot be isolated
Solution Approach 1:
The patent segments the measurement process into two distinct experiments: one without field gradient (maintaining simplicity) and one with field gradient (isolating diffusion effects). By separating the measurements in this way, the patent maintains ease of operation for the first experiment while achieving precise diffusion effect separation in the second experiment, resolving the contradiction between simplicity and precision.
Solution Approach 2:
The patent uses field gradient as an intermediary tool that can be selectively applied. The field gradient acts as a mediator that, when applied in the second experiment, selectively affects water diffusion while leaving oil relatively unchanged, thereby enabling isolation of diffusion influences without complicating the fundamental measurement approach.
3Measurement precision
If field gradient is applied during CPMG echo train, then diffusion influence on water is enhanced, but measurement complexity increases
Solution Approach 1:
The patent divides the measurement into two separate experimental sequences: a standard T1/T2 measurement without field gradient and a second measurement with field gradient applied during the CPMG echo train. This segmentation allows the complex field gradient application to be isolated to only the necessary measurement, reducing overall procedural complexity while achieving the precision needed for water diffusion differentiation.
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 allows for more accurate determination of water cut by effectively isolating the influence of diffusion on water, reducing ambiguity and improving prediction accuracy.
Implementation Method 1
In a second scan with the application of a gradient, the measured T2 (T2app) will be affected solely by water diffusion
Implementation Method 2
The agreement was close, but not close enough. For example, in the experiment shown here, the NMR determined value was 29.9%, while the true value was 28.6%
Data Source
AI summary
A method of incorporating the influence of diffusion into the CPMG-based T2 measurement for one or more of the following: water cut measurement; performing inline measurements of flow rate; density; and rheology of a flowing fluid. The method includes conducting a “standard T1/T2 experiment” at least twice by providing one scan without a field gradient during the CMPG echo train. Then, providing a second scan with the application of a gradient, where in the second experiment the measured T2 (T2app) is affected solely by water diffusion, thus shifting cross peaks which represent water on the first T1/T2 spectrum to lower T2 values on the second spectrum.