Porosity Correction in Formate Mud Filtrate Invaded Formations
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Solution Overview
Problem
In drilling operations, existing methods for logging-while-drilling (LWD) face uncertainties due to invasion of filtrate into the formation and slow-forming mud cake, which affect density and hydrogen index calculations, leading to inaccurate porosity determinations.
Innovation Solution
A method is developed to calculate porosity by determining the bulk and movable fluid pore volumes, adjusting the hydrogen index value for the movable fluid pore volume to correct porosity calculations, while leaving the hydrogen index of the bound fluid pore volume unadjusted, thereby improving accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If hydrogen index adjustment is applied to the entire bulk pore volume, then porosity calculation simplicity is improved, but accuracy deteriorates due to over-correction including bound fluid pores
Solution Approach 1:
The patent segments the bulk pore volume into two distinct components: movable fluid pore volume (invaded by filtrate) and bound fluid pore volume (not invaded). By applying hydrogen index adjustment only to the movable fluid portion, the method achieves accurate porosity calculation without over-correction, resolving the contradiction between simplicity and accuracy.
Solution Approach 2:
The patent applies local quality by differentiating the treatment of different pore regions. The movable fluid pores receive hydrogen index adjustment to account for filtrate invasion, while bound fluid pores maintain their original hydrogen index values. This localized approach ensures accuracy without unnecessary complexity.
2Device complexity
If filtrate invasion is not accounted for in porosity calculations, then calculation complexity is reduced, but measurement precision deteriorates
Solution Approach 1:
The patent uses T2 spectrum analysis to segment pore volumes into movable and bound fluid portions, enabling selective correction for filtrate invasion. This segmentation allows the method to account for invasion effects accurately while maintaining a systematic calculation approach that does notexcessive complexity.
Solution Approach 2:
The patent introduces T2 relaxation time as an intermediary parameter to identify and differentiate between movable and bound fluid pores. This intermediary enables the calculation method to account for filtrate invasion effects without requiring complex direct measurement of invasion, thus maintaining reasonable complexity while improving 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 approach provides a more accurate porosity calculation by accounting for the invasion of filtrate into movable fluid pores only, avoiding over-correction and resulting in a porosity value closer to the actual formation porosity.
Implementation Method 1
In NMR logging, a portion of a geological or rock formation is placed within magnetic fields to alter the magnetic state of the molecules in the formation. The characteristics of the formation are detected, including a T2 spectrum, which corresponds to the times for the molecules to return from an altered magnetic state to a relaxation state.
Data Source
AI summary
A method of calculating a porosity of a geological formation includes determining a bulk pore volume and a movable fluid pore volume in the geological formation in which drilling mud including a mud filtrate is introduced, calculating a porosity of the formation based on a bulk pore volume, and correcting the porosity based on the movable fluid volume in the geological formation.