Abstract
Simultaneous inversion of sonic, density, and electrical resistivity borehole-derived well logs, has been addressed in literature in recent years. However, this problem is not broadly studied for dual-porosity sandstone formations. In addition, most authors presumed salinity and matrix properties as known parameters in their studies. We integrate the conservation of mass to model density, a differential effective medium theory for elastic modeling, and a laboratory-supported model for electrical resistivity of dual-porosity sandstones. Utilizing this methodology, we simulate electrical resistivity, sonic, and density well-log data. We develop a stochastic global search engine to jointly invert petrophysical properties. We build a dual-porosity formation with associated petrophysical properties and show the proposed workflow accurately replicates true well-log responses in the oil column, water leg, and transition zone. Local petrophysical properties (microporosity, intergranular porosity, total porosity, and water saturation) and global model parameters (salinity, matrix properties, critical porosity, resistivity lithology exponents, and sonic length scales for different pore networks) are all well recovered. The developed multiphysics calibrated rock models will assist petrophysicists and seismic analysts to identify and distinguish sandstone facies characteristics from well-log and prestack seismic data.
Highlights
For clean formations, “Archie’s equation” [1] has been employed as the fundamental method for evaluating the presence of hydrocarbons for the last 75 years
We develop an inversion workflow to jointly convert electrical resistivity, density, and sonic well logs into petrophysical properties
L parameters, lithology of each pore system can be explained in Shahin et al [20],and matrix elasticexponents moduli, critical porosity, intergranular obtained from the nonlinear optimization of velocity and resistivity core measurements
Summary
For clean formations, “Archie’s equation” [1] has been employed as the fundamental method for evaluating the presence of hydrocarbons for the last 75 years. Wu and Grana [13] constructed another joint inversion algorithm and tested it on sandstone core and well-log measurements They utilized the Raymer model to simulate Pand S-wave velocities, Archie model to compute electrical resistivity, and linear average equations to express density and gamma ray responses of the composite medium. Primary porosity (termed intergranular ), secondary porosity (termed micropores ), water saturation, matrix density, matrix bulk and shear moduli, salinity, critical porosity, resistivity lithology exponents, and elastic length scales are the petrophysical, matrix, fluid, and model parameters recovered Note that this novel workflow is discriminated from previous studies by the following salient features:. While the best common practice is to estimate fitting parameters (resistivity lithology exponents and sonic length scales for different pore networks) from special core measurements (resistivity, ultrasonic, etc.), we present a new methodology to obtain these parameters from conventional well logs (density, resistivity, and sonic)
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