Evaluation of Thin Limestone Interlayers within Marcellus Shale in Southwestern Pennsylvania

Abstract

Marcellus Shale consists of organic-rich mudrocks with several thin limestone interlayers. The thickest interlayer is named Purcell Limestone, which separates the Marcellus Shale into the Upper Marcellus Shale (Oatka Creek Member) and Lower Marcellus Shale (Union Spring Member). The thickness of these limestone interlayers varies by location within the Appalachian Basin. Limestone interlayers can have an influence on hydraulic fracturing and production in the Marcellus Shale. Identifying the thin limestone interlayers within the Marcellus Shale is important to correctly estimate the thickness of the organic-rich zone within Marcellus Shale. The effects on hydraulic fracturing and production can be investigated by analyzing whether the mechanical properties change within the Marcellus Shale. Hydraulic fractures through the Purcell Limestone is an important area of study in which the thickness of the limestone layer can play a part in some effects. Understanding the varying thickness of the Purcell Limestone will be useful in order to evaluate the Marcellus further. In southwestern Pennsylvania (including Westmoreland, Fayette, Washington and Greene Counties), the Purcell limestone varies in thickness. Analyzing wells that have been drilled in the Marcellus Shale Formation will allow to pick formation tops and consequently make isopach maps for these thin limestone layers and Marcellus Shale. The log data used in this research include gamma ray, bulk density, neutron, PE and resistivity. The thin limestone interlayers may be analyzed further in different wells to figure out the effects on hydraulic fracturing and production for this area. A 3-D structural model will be constructed based on the formation top data and the built maps of structure and isopach of the thin limestone layers and Marcellus shale.

AAPG Datapages/Search and Discovery Article #90335 © 2018 AAPG 47th Annual AAPG-SPE Eastern Section Joint Meeting, Pittsburgh, Pennsylvania, October 7-11, 2018