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The organic-rich shale gas fields underlying the Appalachian, Illinois and Michigan basins are potentially the most productive source of natural gas in the northeast United States. Similarly to the Barnett Shale in Texas and the Fayetteville Shale in Arkansas, considerable volumes of gas are currently produced from these unconventional Devonian shale reservoirs using traditional and more modern well log evaluations techniques and completion methods. Among others, two main geologic factors govern the production from these gas-bearing formations: ultra low matrix porosity and permeability and fracture-induced permeability. Devonian Shales are extremely low porosity reservoirs that must be effectively hydraulically fracture stimulated. Additionally, analysis of these gas fields illustrates how structural geology (by the means of basement structure influence, differential shortening effect, etc.) yields stress field variations both laterally and with depth. To avoid making too many assumptions as to the induced fracture geometry and to better understand the created fracture geometry for various completion designs, monitoring of the induced microseismic activity may be used. Using a couple of examples from various formations (e.g., tight gas sand, shale gas, etc.), this paper highlights how microseismic monitoring of hydraulic fracture treatments can provide key information to characterize fracture development and geometry. |
