Overpressure estimation and productivity analysis for a Marcellus Shale gas reservoir, southwest Pennsylvania: A case study

Abstract

It is well established that geology, geomechanics, and completion play an important role in gas productivity from shale formations. In particular, overpressured shale — along with higher fracture intensity — generally correlates with higher production rates. Conventional pore-pressure prediction techniques do not work well for black shale formations, primarily because a basin has often experienced multiple episodes of tectonic activity and subsequent overpressure generation; secondly, because the recorded petrophysical logs for pore-pressure estimation are significantly affected by the presence of organic content and gas. Overpressure mechanisms and distribution are studied for the Middle Devonian Marcellus Shale Formation of the Appalachian Basin in Pennsylvania to understand their relationship with well productivity. A sonic velocity-density crossplot does not reveal a clear picture of overpressure generation, primarily due to complex geologic history and distinct compositional variation between Marcellus Shale and overburden shale. 1D pore pressure was estimated from sonic velocity using traditional methods with pressure reference trend for the Marcellus Shale interval in the drilled wells and calibrated to the available in situ pressure measurements. 3D pore pressure was then estimated with upscaled 1D pore-pressure profiles and 3D seismic velocity data. Results suggest that the area having higher overpressure of about 160 psi produces about 55% more gas than the lower overpressure area. Further, understanding the spatial variation of overpressure in the study area may facilitate better field development planning.

Pre-drill pore pressure prediction from 1D seismic velocity profile to 3D modeling using high resolution full waveform inversion velocity (FWI): deep water offshore, West Nile Delta

“…The literature has mentioned several methods to predict over pressured intervals pre-drill using seismic velocity data (see Eaton 1975;Heppard and Albertin 1998;Badri et al 2000;Carcione and Helle 2002;Sayers et al 2002;Chopra and Huffman 2006;Sundaram and Jain 2008;Lu et al 2009;Babu and Sircar 2011;Brahma et al 2013;Karthikeyan et al 2018;Das and Mukherjee 2020).…”