NMR Logging Micro-Porosity Dual First-Echo Method
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Solution Overview
Problem
Existing NMR logging methods are inaccurate in estimating micro-porosities due to the second-order stimulated-echo effect, leading to distortions in NMR signals, particularly in formations with micro-porosity such as shale gas, shale oil, clay-bound water, heavy oil, and carbonates, resulting in estimates that can be off by 20% or more.
Innovation Solution
A dual first-echo method is employed, involving at least two NMR measurements with very short wait times (less than 100 milliseconds) and different first-echo times (e.g., 0.4 ms and 0.5 ms), with simultaneous processing of the first-echoes to reduce or eliminate the distortion caused by the second-order stimulated-echo effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional NMR logging methods are used, then NMR measurements can be performed in geological formations, but the estimates of micro-porosity are inaccurate due to the second-order stimulated-echo effect causing signal distortion
Solution Approach 1:
The patent changes the timing parameters of the NMR pulse sequence by using very short wait times (less than 100 milliseconds) and different first-echo times (e.g., 0.4 ms and 0.5 ms) to minimize the development of the second-order stimulated-echo effect, thereby improving micro-porosity estimation accuracy
Solution Approach 2:
The patent segments the NMR measurement process into multiple separate measurements with different timing parameters, processing the first-echoes simultaneously to reduce the harmful effects of the second-order stimulated-echo effect on micro-porosity estimation
2Reliability
If longer wait times are used to polarize all formation fluid, then complete polarization is achieved, but the measurement time increases and fast decaying porosity information is lost
Solution Approach 1:
The patent applies partial action by using short wait times that do not fully polarize all formation fluid, but are sufficient to capture fast decaying porosity information before it relaxes, accepting incomplete polarization as a trade-off for preserving fast transient signals
Solution Approach 2:
The patent rushes through the measurement process by using very short wait times and different first-echo times to capture fast decaying porosity information before the stimulated-echo effect develops, completing the measurement quickly to preserve transient signals
3Measurement precision
If dual-TE method with long wait times is used, then fluid diffusion coefficient can be determined, but the second-order stimulated-echo effect still distorts the NMR signal in micro-porosity formations
Solution Approach 1:
The patent changes the timing parameters by using very short wait times (less than 100 milliseconds) and different first-echo times, which minimizes the second-order stimulated-echo effect while still enabling fluid diffusion coefficient determination through the dual measurement approach
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 accurate estimates of porosity and T2 relaxation times, reducing inaccuracies associated with the second-order stimulated-echo effect and improving the precision of NMR logging in formations with micro-porosity, enhancing the reliability of hydrocarbon reserve assessments and wellbore stability evaluations.
Implementation Method 1
Nuclear magnetic resonance (NMR) tools are one type of downhole tools that are particularly useful for performing detailed measurements of properties of hydrocarbon bearing formations or overburden shale
Implementation Method 2
an NMR effect, here referred to as the second-order stimulated-echo effect, disturbs the amplitude of indirect NMR echoes
Data Source
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AI summary
A method for estimating a property of a subsurface material includes: conveying a carrier through a borehole penetrating the subsurface material; performing at least two magnetic resonance (NMR) measurements in a volume of interest in the subsurface material using an NMR tool disposed on the carrier, wherein (i) a first NMR measurement has a first wait time and a first first-echo time and a second NMR measurement has a second wait time and a second first-echo time, (ii) the first wait time and the second wait time are less than or equal to 500 milliseconds, and (iii) the first first-echo time and the second first-echo time are different; receiving at least the first-echo of the first NMR measurement and receiving at least the first-echo of the second NMR measurement; and estimating the property of the subsurface material by using the at least two measured first-echoes simultaneously.