Stochastic Formation Evaluation for Variable Water Salinity
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Solution Overview
Problem
In mature water flooded reservoirs, existing formation evaluation techniques face challenges in accurately determining water saturation and hydrocarbon reserve calculations due to varying water salinity, which can lead to erroneous results and high uncertainty, especially when matrix and fluid petrophysical properties are not accurately known or available.
Innovation Solution
A stochastic approach is employed to estimate variable water salinity using nuclear measurements alone, eliminating the need for knowledge of matrix petrophysical properties or hydrocarbon properties, and reducing uncertainties related to resistivity equation and parameter selection, by generating an equation of state based on log measurements and determining constituent compliance factors and likelihoods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing formation evaluation techniques are used in variable water salinity environments, then water saturation and reserve calculations can be performed, but the results become erroneous and uncertain when matrix and fluid petrophysical properties are not accurately known
Solution Approach 1:
The patent changes the approach from using traditional petrophysical parameters (matrix and fluid properties) to using nuclear magnetic resonance (NMR) measurements and dielectric measurements. This parameter change allows direct measurement of fluid properties without relying on assumed matrix properties, thereby resolving the contradiction between measurement precision and reliability in variable salinity environments
Solution Approach 2:
The patent introduces an intermediary approach by using NMR and dielectric measurements as intermediate steps between traditional resistivity measurements and final water saturation determination. These intermediate measurements provide direct information about fluid properties and saturation states, bypassing the need for accurate matrix property knowledge and improving both precision and reliability
2Productivity
If traditional resistivity-based formation evaluation methods are applied, then water saturation can be estimated, but uncertainties increase significantly in variable water salinity environments where petrophysical properties are unknown
Solution Approach 1:
The patent applies multi-functionality by using NMR measurements to simultaneously determine multiple parameters including water saturation, hydrocarbon type, and formation properties. This universal approach replaces multiple specialized measurements and calculations, improving both efficiency and precision in variable salinity environments without requiring prior knowledge of petrophysical properties
3Measurement precision
If accurate knowledge of matrix and fluid petrophysical properties is required for formation evaluation, then water saturation can be determined using traditional methods, but the complexity and data requirements increase
Solution Approach 1:
The patent implements self-service by using NMR and dielectric measurements that directly characterize the formation fluids and properties without requiring external input data about matrix or fluid petrophysical properties. The measurements themselves provide all necessary information, eliminating the need for separate property characterization steps and reducing overall system complexity while maintaining high precision
Data Source
AI summary
A method for determining a volume of a constituent(s) in a geological formation may include generating an equation of state based upon log measurements for the geological formation, with the equation of state providing a correlation between the log measurements, determining a quality factor for the equation of state, and for each of a plurality of different constituents expected to be in the formation, determining a constituent compliance factor for each of the constituents. The method may further include determining an uncertainty for each constituent compliance factor, determining a likelihood that each constituent is present in the formation based upon the quality factor, the constituent compliance factor for the constituent, and the uncertainty for the constituent compliance factor, generating a volumetric model based upon the log measurements and the determined likelihoods of the constituents in the formation, and determining the volume of the constituent(s) based upon the volumetric model.