Porosity Measurement Correction for Gas-Bearing Formations
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Solution Overview
Problem
Current porosity measurement techniques in underground formations are inaccurate due to the presence of gases and mud-filtrate invasion, leading to incorrect estimates of oil and gas reserves, as they fail to account for varying substances and invasion profiles, especially in Logging While Drilling (LWD) applications.
Innovation Solution
A method involving multiple porosity measurements taken at different times and depths, combined with known gas characteristics and mud-filtrate penetration data, to correct for gas presence and invasion effects, using techniques like Neutron-Gamma Density measurements and time-lapse logging to determine accurate porosity by projecting measurements onto a 'Mud-Filtrate Line' and 'Gas Characteristic Saturation Lines'.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional porosity measurement techniques are used, then the measurement process is simple and quick, but the measurement precision deteriorates due to gas presence and mud-filtrate invasion
Solution Approach 1:
The measurement method segments the formation into distinct zones (invaded zone and virgin zone) and uses multiple measurements at different radial depths to separately characterize each zone's properties, allowing for corrected porosity calculations that account for mud-filtrate invasion and gas presence
Solution Approach 2:
The patent introduces an intermediary correction model that uses known gas characteristics and mud-filtrate properties as mediating parameters to transform apparent porosity measurements into corrected porosity values, eliminating the direct impact of gas and invasion effects
2Measurement precision
If multiple porosity measurements are taken to account for gas and invasion effects, then measurement precision improves, but the time required for measurement increases
Solution Approach 1:
The patent performs preliminary actions by obtaining gas characteristics and mud-filtrate properties before the main porosity measurements, allowing the correction calculations to be performed efficiently during the measurement process without requiring additional time for these parameter acquisitions
3Productivity
If LWD measurements are taken shortly after drilling, then productivity is improved by immediate measurement, but measurement precision deteriorates due to shallow mud-filtrate invasion
Solution Approach 1:
The patent employs dynamic correction factors that adapt to the varying depth of mud-filtrate invasion, allowing the measurement system to maintain high precision despite the time variable by continuously adjusting calculations based on the current invasion profile
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 porosity measurements by accounting for gas presence and mud-filtrate invasion, reducing errors associated with gas-bearing formations and shallow invasion zones, thereby improving the estimation of underground reserves.
Implementation Method 1
Neutron-Gamma Density measurements
Implementation Method 2
Neutron-Gamma Density measurements
Data Source
AI summary
This disclosure relates to methods and apparatuses for determining the porosity of a formation surrounding a borehole. A drilling fluid penetrates a distance into the formation as a function of time. First and second porosity measurements are taken, both at a first time and at a second time. The first porosity measurement is of a type selected to indicate a different porosity measurement in the presence of a gas as compared to the second porosity measurement. The first and second porosity measurements are selected to have substantially the same depth-of-investigation into the formation and are affected approximately proportionally by the gas.