Drilling Fluid Slowness Determination in Borehole Annulus

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Solution Overview

Problem

Accurately determining the slowness of drilling fluid in the annulus of a borehole is challenging due to the presence of rock cuttings, which complicates direct measurement and affects the accuracy of formation property calculations in logging-while-drilling environments.

Innovation Solution

A method and system that use a downhole tool with acoustic apparatus to measure formation slownesses, determine formation compressibility and density, and calculate the slowness of the drilling fluid in the annulus by correcting the internal drilling fluid properties based on rock cutting concentration and flow rate, iteratively refining the estimate until convergence.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If direct measurement of drilling fluid properties is performed in the annulus, then measurement precision may be improved, but the difficulty of detecting and measuring increases due to rock cuttings presence

Engineering Contradiction:

Improvedrilling fluid slowness measurementVSAvoiddrilling fluid property measurement

Core Design Contradiction:

Measurement precisionVSDifficulty of detecting and measuring

Solution Approach 1:

The patent uses formation properties (compressibility and density) as intermediary parameters to indirectly determine drilling fluid slowness in the annulus. Instead of directly measuring the difficult-to-access drilling fluid properties, the system measures formation properties and uses them to calculate the drilling fluid slowness through established relationships, effectively using the formation as a mediator to obtain the desired information.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces direct mechanical/acoustic measurement of drilling fluid properties with a calculation-based approach. By measuring formation slowness and using formation compressibility and density, the system substitutes direct drilling fluid measurement with an indirect calculation method that avoids the difficulties of measuring through rock cuttings in the annulus.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Loss of information

If acoustic measurements are used to determine formation parameters, then formation property understanding is improved, but accuracy deteriorates without proper accounting of drilling fluid effects

Engineering Contradiction:

Improveformation property accuracyVSAvoidformation parameter determination

Core Design Contradiction:

Loss of informationVSReliability

Solution Approach 1:

The patent implements a feedback mechanism where the measured formation properties and calculated drilling fluid properties are used iteratively to improve measurement accuracy. The system uses the determined formation compressibility and density to calculate drilling fluid slowness, which then feeds back into the acoustic measurement process to refine formation parameter determination, creating a closed-loop system that continuously improves accuracy.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent changes the approach from directly measuring drilling fluid parameters to calculating them based on formation parameters. By measuring formation slowness and deriving formation compressibility and density, then using these to calculate drilling fluid slowness, the system transforms the measurement problem into a parameter transformation and calculation process that accounts for drilling fluid effects on acoustic propagation.

Inventive Principle:

Principle #35Parameter changes

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

Improves the accuracy of formation property measurements by accurately estimating the slowness of the drilling fluid in the annulus, enhancing the precision of acoustic formation analysis.

Implementation Method 1

sonic or acoustic measurements may be obtained using a downhole tool to determine formation parameters

Methodology Applied

Scientific EffectAcoustic wave propagation: Sound

Implementation Method 2

measuring with a downhole tool slownesses of the formation based on the first slowness

Methodology Applied

Scientific EffectTime of flight: Time of Flight

Implementation Method 3

determining a first compressibility of the formation based on the slownesses of the formation and a first density of the formation

Methodology Applied

Scientific EffectAcoustic impedance relationship:

Implementation Method 4

calculating a second density and a second compressibility of the drilling fluid in the annulus based on the first density and the first compressibility

Methodology Applied

Scientific EffectMixture density calculation:

Data Source

PatentUS8773948B2Methods and apparatus to determine slowness of drilling fluid in an annulus

Publication Date: 2014.07.08 SCHLUMBERGER TECH CORP

AI summary

Methods and apparatus to determine slowness of drilling fluid in an annulus are described. An example method of determining slowness of drilling fluid in an annulus of a borehole in a formation includes obtaining a first slowness of the drilling fluid in the annulus and measuring with a downhole tool slownesses of the formation based on the first slowness. The example method also includes determining a first compressibility of the formation based on the slownesses of the formation and a first density of the formation and calculating a second density and a second compressibility of the drilling fluid in the annulus based on the first density and the first compressibility. The method also includes calculating a second slowness of the drilling fluid in the annulus based on the second density and the second compressibility.