UNDERSTANDING TRANSIENT GOB GAS FLOW BEHAVIOR IN LONGWALL GOB AREAS TO OPTIMIZE GOB GAS REMOVAL TECHNIQUES

THIS RESEARCH IS INVESTIGATING METHODS OF OPTIMIZING THE REMOVAL OF GOB REGION GAS THROUGH THE USE OF VERTICAL AND HORIZONTAL VENTILATION BOREHOLES. RESEARCH TASKS INCLUDE THE COLLECTION OF TRANSIENT PRESSURE DATA FROM EXISTING GOB WELLS. THESE DATA WILL BE EVALUATED TO PROVIDE ESTIMATES OF THE VOLUME AND PROPERTIES OF THE GOB REGION. THE PRODUCTION AND PRESSURE PERFORMANCE OF THE GOB REGION WILL BE SIMULATED WITH A FINITE-DIFFERENCE, COALBED METHANE RESERVOIR MODEL THAT CAN INCLUDE COAL AND NONCOAL STRATA. OPTIMIZATION OF THE GOB GAS PRODUCTION WILL BE ACCOMPLISHED BY PREDICTING THE GOB REGION PERFORMANCE WITH VARIOUS NUMBERS OF VERTICAL AND HORIZONTAL BOREHOLES. PRESENT ESTIMATES OF THE NUMBER OF GOB WELLS REQUIRED FOR EFFICIENT GOB GAS REMOVAL, SPACING, AND PLACEMENT ARE BASED ON PAST EXPERIENCE OR ON TRIAL AND ERROR RATHER THAN ON ENGINEERING DESIGN. UNFORTUNATELY, BECAUSE OF PERMEABILITY RESTRICTIONS THAT ARE NOT YET FULLY UNDERSTOOD, LIMITED NUMBERS OF VERTICAL GOB VENTILATION BOREHOLES ARE NOT ALWAYS SUFFICIENT TO ACCOMMODATE GOB EMISSIONS. SPECIFIC PROBLEMS TO BE ADDRESSED BY THE RESEARCH IN PHASE I INCLUDE (1) METHODS OF INSTALLING A SURFACE RECORDING DOWNHOLE PRESSURE GAUGE IN A GOB WELL, (2) THE WELL TESTING PROCEDURES REQUIRED TO COLLECT SUFFICIENT DATA FROM WHICH TO EVALUATE THE VOLUME AND FLOW PROPERTIES OF THE GOB REGION CONTRIBUTING TO PRODUCTION, (3) THE ANALYSIS METHODOLOGY REQUIRED TO ESTIMATE GOB REGION PROPERTIES FROM THE PRESSURE DATA, AND (4) METHODS OF RESERVOIR SIMULATION REQUIRED TO ESTIMATE FUTURE GOB WELL PERFORMANCE AND TO OPTIMIZE GOB WELL DESIGN.