Quantitative interpretation of geological and geophysical well data
Abstract
Geophysical and geological properties of rocks are analyzed using a search for internal consistency between geophysical log measurements, composition estimates from core or cuttings, stratigraphically controlled predictions of properties from adjacent wells, comprehensive interpretation equations, and rigorous solution uncertainty estimates. Routine analyses are made using a gradient descent simultaneous equation solution. Assumptions in the gradient descent algorithm are checked using a maximum likelihood solution technique. The analysis technique is tested on a cored interval of the Dakota Sandstone, in the San Juan Basin, New Mexico. Thirty-two core samples were taken, each with 13 log measurements and measurements of 14 geologic properties. A log interpretation with all log and geologic information verifies correctness of interpretation equations and mineral properties. Reanalysis of logs, with core porosity assumed unknown, verifies that log estimates of mineralogy and porosity match well with the core measurements. Uncertainties on compositions estimated from only logs are consistent with errors between core measurements and log estimates. A statistical summary of log analysis results in the cored well is then used to constrain log analyses on various log suites in an adjacent well. Interpretations first compare full log suites with, and without, the stratigraphically controlled predictions, and are found to match closely. A second comparison of the full log suite interpretation with results from interpretation of the spontaneous potential and deep induction resistivity logs show that the stratigraphic information allows some properties to be accurately estimated while others are not resolved. A comparison of the gradient descent solution with the maximum likelihood solution indicates that true solution distributions are probably multimodal and asymmetric. The gradient descent algorithm only finds a local error minimum in the solution space, does not locate other acceptable solutions, and underestimates the range of acceptable solutions found by the maximum likelihood technique.
Subject Area
Geophysics
Recommended Citation
Baker, Mark Richard, "Quantitative interpretation of geological and geophysical well data" (1988). ETD Collection for University of Texas, El Paso. AAI8911139.
https://scholarworks.utep.edu/dissertations/AAI8911139