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UBC Theses and Dissertations

Evaluation and application of Fracture Detection Software to coalbed methane exploration Rozak, Alexander Thomas

Abstract

Natural fractures, or cleats, form the only permeable pathway for desorbed methane to travel from the coal matrix to a well bore for production. Hence, detection and delineation of natural fracture systems is of prime importance to coalbed methane exploration. This thesis evaluates an industry developed software package for detecting subsurface fractures in coals. This software package, known in industry as "LogFAC", re-interprets conventional geophysical well log data to estimate permeability in target coal seams. LogFAC hypothesizes that fractures form the main permeable pathways and as such measurements of fracture porosity are strongly tied to permeability, and that this relationship is reflected in gas production. During drilling operations, drilling fluids invade into the surrounding rock. Because invasion in coal occurs through fractures traversing the impermeable coal matrix, measured of depth of invasion is related in some manner to fracture porosity. Zones of greatest fracture porosity are also be the most permeable and produce the most methane. By using well log and drilling mud data, LogFAC estimates the volume of fluid invaded coal and the amount of fluid available to create this invasion. The larger the fluid to coal ratio, the larger and more well developed the fracture system. Although the software provides measurements in the volume domain and it is tempting to define results as porosity, this thesis demonstrates that permeability, or some aspect more affinitive to permeability than porosity, is being defined. This thesis comprises four chapters. Chapter one examines aspects of the theoretical basis for the software and illustrates experimental results consistent with LogFAC theory. Chapter two examines the ability of the software to correlate existing geophysical well log data to historical coalbed methane production from the San Juan Basin of Colorado and New Mexico. Chapter three illustrates an application of LogFAC as a predictive exploration tool, and outlines a play concept and results from a test drill program that indicates that LogFAC successfully located reservoir quality coals in the Western Canada Sedimentary Basin. The fourth and final chapter summarizes the study and provides recommendations for further research.

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