John Ely, S.A. Holditch & Associates Inc.
Past studies by DOE, NPC, and GRI confirm that an enormous volume of gas is trapped in low permeability reservoirs. However, neither current technology nor price is adequate to allow widespread development of these reservoirs. To better understand the fracturing process and, thus, be able to eventually improve technology, it is first necessary to improve our understanding of the low permeability reservoirs that are being fracture treated. The Gas Research Institute (GRI) is sponsoring research in which comprehensive efforts are being undertaken to perform geological, coring, logging, well testing, fracture treatment monitoring, and fracture diagnostic studies on selected wells in two targeted basins, the Travis Peak formation in East Texas and the Corcoran and Cozette formations of the Piceance Basin. This paper summarizes the research effort which has as its ultimate goal to learn how to measure and analyze data so that fracture dimensions can be calculated in real time, or as the fracture treatment is being pumped. Eventually, we hope to be able to alter the design during a treatment in order to control fracture shape. Engineers and scientists are being placed in the field with computers so they can analyze the data while the job is being pumped. Several cooperative wells in East Texas have been drilled and analyzed. Additionally, the first of four Staged Field Experiments has been completed. The Staged Field Experiments are wells drilled where GRI is in complete control of the entire operation allowing more latitude with experimentation not possible in cooperative wells. Conventional whole cores (up to 400 feet per well) have been taken. The cores have been used to determine regional and local environments of depositions. Complete suites of open hole logs have been run and used to calculate rock and mechanical properties. Log interpretation results have been found to compare favorably with the core analysis results. In-situ stress tests have been run and compared to the log and core data. Fracture treatments are being monitored and analyzed. Post-fracture well tests are run to estimate the effectiveness of the fracture treatments. Also included in the paper is a documentation of the monitoring equipment that has been designed and developed by GRI contractors. Included are mobile Qualit Control (QC) laboratories and a new generation rheology unit that measures both couette and capillary viscosity at bottomhole temperatures. The unit also is designed such that fluid leakoff anticipated in the formation can be simulated.