Using XRF, SEM and Pyrolysis for an Economic Appraisal of the Marcellus Formation of Western Pennsylvania for Fracking Purposes

Abstract

An analysis of a core from the Marcellus Formation of Western Pennsylvania was undertaken using 3 laboratory tools; an XRF, SEM with EDX capability and a HAWK pyrolysis instrument. A 4th parameter was porosity measurements from a PHIE and PHIT neutron emitting tool,. Unexpected relationships emerged from a comparison between the various downhole curves. Hydrocarbons that were generated from kerogen pyrolysis (S2) varied directly with the neutron probe's total porosity. Macroporosity (SEM >5 microns) varied more closely with the TOC. Macroporosity also varied with the siliceous microfossil content, particularly radiolaria within the Marcellus and unknown shell hash in the overlying Burkett and paralleled the free silica. The “free oil” S1 showed a similar distribution to the S2 and indicated 3 prospective sweetspots; Lower Marcellus, Upper Marcellus and Burkett. Carbonate horizons showed low porosity, due to the presence of clay. The SEM also showed the limestones were extensively bioturbated, shelly and phosphatic. Pyrolysis showed they had low TOC. The carbonate rich relatively oxidizing paleoenvironment allowed for the presence of burrowing organisms. The rest of the Marcellus seemed to have been deposited under very anoxic conditions and was largely composed of silty clay, siltiest near the base of the formation. The zones of lowest clay content (Middle of the Lower Marcellus "transgressive systems tract") also had highest macroporosity, highest oil content (S1, S2), and probably correspond to the best sweet spot. Organic richness is very good within the Marcellus, ranging between 2 and 12 % TOC and so is the source potential (S2 often greater than 5 mg hydrocarbons/g rock). The Burkett - Tully Limestone often had greater than 2% TOC. Tmax maturity data showed the Marcellus to lie in the condensate/wet gas window (Tmax of 455 – 475 °C). The Lower Marcellus sweet spot had a relatively low clay and high silt content that makes it the best, candidate for fracking. This zone had good brittleness and high hydrocarbons content (S1 and S2). At the base of the Marcellus and immediately above the Onondaga Limestone, a very thin zone of extreme ductility occurs, that probably corresponds to a bentonitic ash layer. The combination of detailed lithological analyses with an appraisal of the hydrocarbons within the Marcellus and adjacent Formations, allows their zonation in terms of potential economic productivity and engineering suitability for fracking purposes.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015