The Antrim Shale, first drilled in the 1940’s, is estimated to contain significant quantities of gas, up to 76 Tcf in place. However, relatively low gas production rates, coupled with an inadequate understanding of its key reservoir properties, have limited its active pursuit. Recently, a better appreciation of the merit of the Antrim Shale as a gas resource has raised operator interest. From a base of 32 Antrim Shale wells in 1986, drilling increased to 91 wells in 1987 and to over 300 wells in 1988.
While the pace of Antrim Shale drilling has clearly increased, gas production rates are still relatively low (at about 100 Mcf/day), suggesting that innovative completion and stimulation techniques are needed to increase production and, ultimately, gas reserves. This paper examines in detail two such development strategies aimed at improving Antrim Shale productivity - large volume sand fracs and improved geologic understanding.
Initial analysis of the Antrim Shale suggests that large, water-based stimulation treatments may increase gas flow by more efficiently removing the water in the formation thus improving relative permeability to gas. In addition proper interval selection and well spacing could improve gas recovery. A tworphase, dual porosity reservoir simulator was used to examine the well performance and gas flow rates for applying improved technology to the Antrim Shale.