Downhole Mud Gas Sampling for Accurate Formation Analysis
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Solution Overview
Problem
Current mud-gas logging techniques face challenges in accurate depth control and sample dilution, leading to unreliable hydrocarbon gas analysis, particularly in thin reservoirs, due to inaccurate pump rates and gas diffusion within the mud, and the need for sensitive instrumentation to account for air dilution and background gas levels.
Innovation Solution
Implementing downhole measurements by obtaining pre-bit and post-bit samples near the drill bit, separating and analyzing solid and fluid components using techniques like chromatography, mass spectrometry, and optical spectroscopy to determine formation properties, allowing for real-time analysis and reducing the impact of mud properties and gas diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If surface mud-gas analysis is used, then hydrocarbon gas composition can be determined, but depth control and sample dilution issues reduce measurement precision
Solution Approach 1:
The patent takes preliminary action by collecting gas samples at the drill bit location before the mud returns to the surface. This pre-empts the dilution and diffusion problems that occur during mud circulation, allowing accurate depth control and reliable hydrocarbon analysis without the need to infer depth from circulation rates.
Solution Approach 2:
The patent introduces an intermediary sampling system at the drill bit that directly captures gas samples without relying on the mud stream. This intermediary mechanism separates the gas sampling process from the mud circulation system, eliminating the effects of pump rate inaccuracies and gas diffusion within the mud.
2Device complexity
If gas diffusion within mud is not accounted for, then analysis can be simplified, but measurement precision deteriorates in thin reservoirs
Solution Approach 1:
The patent extracts the gas sampling process from the mud stream by collecting gas directly at the drill bit. This extraction eliminates the gas diffusion problem within the mud entirely, as the gas is sampled before it can diffuse through the mud column, maintaining both simplicity and precision.
3Measurement precision
If sensitive instrumentation is used to account for air dilution, then analysis accuracy improves, but device complexity increases
Solution Approach 1:
The patent performs preliminary action by sampling gas at the drill bit before it mixes with air and other gases in the mud stream. This timing ensures that the gas sample has not been diluted, allowing the use of simpler, less sensitive instrumentation while maintaining high accuracy.
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 method provides more accurate and reliable analysis of formation characteristics, such as fluid content and hydrocarbon maturity, by comparing pre-bit and post-bit measurements, enabling better identification of hydrocarbon-bearing intervals and reservoir properties in real-time, reducing the need for laboratory analysis and improving depth control.
Implementation Method 1
analyzing the components. The analysis of the phase (ie. gas), to determine composition and concentration of the constituents, can include, for example, one or more of the following techniques: gas chromatography, mass spectroscopy
Implementation Method 2
The analysis of the liquid phase, to determine composition and concentration of the constituents, can include, for example, one or more of the following techniques: chromatography (ie. gas)
Implementation Method 3
The analysis of the liquid phase, to determine composition and concentration of the constituents, can include, for example, one or more of the following techniques: chromatography (ie. gas), mass spectrometry, optical spectroscopy
Data Source
AI summary
A method for determining a property of formations surrounding an earth borehole being drilled with a drill bit at the end of a drill string, using drilling fluid that flows downward through the drill string, exits through the drill bit, and returns toward the earth's surface in the annulus between the drill string and the periphery of the borehole, including the following steps: obtaining, downhole near the drill bit, a pre-bit sample of the mud in the drill string as it approaches the drill bit; obtaining, downhole near the drill bit, a post-bit sample of the mud in the annulus, entrained with drilled earth formation, after its egression from the drill bit; implementing pre-bit measurements on the pre-bit sample; implementing post-bit measurements on the post-bit sample; and determining a property of the formations from the post-bit measurements and the pre-bit measurements.