Logging-While-Drilling Electromagnetic Tool for Water Saturation and CEC
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current models for log interpretation of shaly sand reservoirs, such as the Waxman and Smits model and dual water model, fail to explicitly predict electrical conductivity with respect to rock structure, spatial fluid distribution, wettability, or clay mineral distribution, and require laboratory measurements for formation water salinity and cation exchange capacity, which are uncertain and not representative of downhole conditions.
Innovation Solution
A method using logging-while-drilling electromagnetic measurement data to calculate water saturation and cation exchange capacity from resistivity log data, involving in-phase and quadrature-phase conductivity components, and formation parameters like grain density, counter-ion mobility, and electric formation factor, allowing for continuous downhole measurement across the reservoir.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If laboratory measurements are used to determine formation water salinity and cation exchange capacity, then these parameters can be obtained, but the measurements are uncertain and not representative of downhole conditions
Solution Approach 1:
The patent replaces laboratory mechanical/chemical measurement systems with an electromagnetic measurement system operated downhole. The electromagnetic tool measures resistivity directly in the formation at reservoir conditions, eliminating the need for core sample retrieval, laboratory preparation, and analysis. This substitution of measurement methodology provides both precision and reliability by measuring in-situ at downhole conditions.
Solution Approach 2:
The patent uses electromagnetic fields as an intermediary to indirectly measure formation water salinity and cation exchange capacity. Rather than directly measuring these parameters, the system measures resistivity and uses theoretical models (Waxman-Smits, Dual Water) to derive salinity and CEC values. This intermediary approach allows measurement of parameters that are difficult to measure directly while maintaining accuracy under downhole conditions.
2Loss of information
If conventional wireline array induction measurements are used, then formation evaluation data can be obtained, but these measurements are not performed in highly deviated and/or horizontal wells
Solution Approach 1:
The patent adapts the measurement system for dynamic drilling conditions by integrating the electromagnetic tool into the drilling assembly that can operate in highly deviated and horizontal wells. The system dynamically adjusts to different well configurations and continuously acquires resistivity data during the drilling process, unlike static wireline measurements that require the well to be completed and accessible.
Solution Approach 2:
The patent performs formation evaluation measurements preliminarily during the drilling process itself, before the well is completed and before wireline logging can be performed. This preliminary action ensures that formation evaluation data is available for well planning and directional drilling decisions without requiring separate measurement campaigns later.
3Device complexity
If formation water salinity is assumed constant within the hydrocarbon column, then simplification is achieved, but actual variations in salinity are not captured
Solution Approach 1:
The patent segments the hydrocarbon column into multiple depth intervals and calculates formation water salinity independently for each interval using resistivity measurements. This segmentation approach reveals vertical salinity variations within the column that would be missed by assuming constant salinity, while still maintaining a systematic and manageable measurement and calculation framework.
Solution Approach 2:
The patent allows formation water salinity to vary as a parameter with depth rather than treating it as a constant. By using the relationship between resistivity, porosity, saturation, and salinity in the Waxman-Smits and Dual Water models, the system calculates salinity values that change with depth, capturing the actual physical variations in the reservoir.
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
Enables accurate and continuous calculation of water saturation and cation exchange capacity at reservoir conditions, improving well placement, formation evaluation, geological modeling, and reservoir management, and enhancing geo-steering in drilling operations.
Implementation Method 1
obtaining resistivity log data measured by a logging-while-drilling electromagnetic tool
Implementation Method 2
in-phase and quadrature-phase conductivity components
Data Source
AI summary
A method for characterizing a subterranean formation is provided that involves obtaining resistivity log data measured by a logging-while-drilling electromagnetic tool operated while drilling a wellbore that traverses the subterranean formation, and calculating at least one of a first data value representing water saturation of the subterranean formation and a second data value representing cation exchange capacity (CEC) of the subterranean formation from the resistivity log data. In embodiments, the method can further involve storing at least one of the first data value and the second data value in computer memory, and/or outputting at least one of the first data value and the second data value as part of a log for well placement, formation evaluation. geological modeling, or reservoir management. The first data value and/or the second data value can also be used for geo-steering the drilling of the wellbore.