Abstract
The Utica/Point Pleasant Formations comprise a major unconventional gas resource in the Appalachian Basin. Core samples from several boreholes in Ohio, West Virginia and Pennsylvania were studied to determine mineralogy, microtexture/microfabric, accessible pore surface area, porosity and pore size distribution as a function of maturity in the Utica/Point Pleasant sub-basin. This effort compares shallower, generally more phyllosilicate-rich Utica intervals with deeper, more carbonate-rich Point Pleasant intervals, the latter representative of horizons currently targeted for gas recovery. The Point Pleasant Formation contains mostly calcite (in the form of fossil tests, grains, and cements), distributed within alternating carbonate- and phyllosilicate-rich matrix laminae, as well as coarse-grained fossil-rich laminae. In both Utica and Point Pleasant core samples, the greatest mercury-accessible connected porosity measurements are associated with the highest maturity samples, an observation that is particularly pronounced for the Point Pleasant. More detailed vertical sampling and analysis of core from a well in Harrison County, Ohio (a region that has experienced copious shale gas production) shows that surface area, pore volume and pore connectivity increase locally in target horizons identified for gas recovery. Observations suggest that optimal mixtures and arrangements of minerals and organic matter, as well as increasing maturity, contribute to forming this productive carbonate-rich unconventional resource. In particular, early diagenetic calcite and quartz cement and increasing quantities of silt-sized particles are associated with higher measured connected porosities, while later-stage matrix dolomitization and recrystallization of fossil laminae tend to occlude the pore network.
| Original language | English |
|---|---|
| Article number | 105345 |
| Journal | Marine and Petroleum Geology |
| Volume | 134 |
| DOIs | |
| State | Published - Dec 2021 |
Funding
ERB, SAW, and JMS received partial support from the National Science Foundation Dimensions of Biodiversity (award no. EAR-1847684 ). Work was also supported by our industry partners, Chesapeake Energy and Gulfport Energy . TL and DRC received partial support from the U.S. Department of Energy , Office of Basic Energy Sciences , under Contract No. DE-SC0006878 (Division of Chemical Sciences, Geosciences, and Biosciences), Geosciences Program. Work by JMS and AMS at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 . We thank Adam J. Rondinone for help with the helium ion microscopy conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility at Oak Ridge National Laboratory. AMS, SAW and JMS were participants in the CNMS User Program, proposal CNMS2016-109. Work by LMA was supported by the U.S. Department of Energy , Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division. Sample analyses at the Ohio State University were done in the Subsurface Energy Materials Characterization and Analysis Laboratory (SEMCAL). We thank the Ohio Geological Survey, and in particular the late Gregory A. Schumacher, for help with obtaining core samples, and Dustin Crandall from NETL for providing XCT imagery of core samples. This manuscript benefitted from the careful review of T.J. Kneafsey at LBNL and two anonymous reviewers. The authors state that they have no conflicts of interest to declare. ERB, SAW, and JMS received partial support from the National Science Foundation Dimensions of Biodiversity (award no. EAR-1847684). Work was also supported by our industry partners, Chesapeake Energy and Gulfport Energy. TL and DRC received partial support from the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-SC0006878 (Division of Chemical Sciences, Geosciences, and Biosciences), Geosciences Program. Work by JMS and AMS at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. We thank Adam J. Rondinone for help with the helium ion microscopy conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility at Oak Ridge National Laboratory. AMS, SAW and JMS were participants in the CNMS User Program, proposal CNMS2016-109. Work by LMA was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division. Sample analyses at the Ohio State University were done in the Subsurface Energy Materials Characterization and Analysis Laboratory (SEMCAL). We thank the Ohio Geological Survey, and in particular the late Gregory A. Schumacher, for help with obtaining core samples, and Dustin Crandall from NETL for providing XCT imagery of core samples. This manuscript benefitted from the careful review of T.J. Kneafsey at LBNL and two anonymous reviewers. The authors state that they have no conflicts of interest to declare.
| Funders | Funder number |
|---|---|
| Chesapeake Energy and Gulfport Energy | |
| Ohio Geological Survey | |
| National Science Foundation | EAR-1847684 |
| U.S. Department of Energy | |
| Office of Science | DE-AC02-05CH11231 |
| Basic Energy Sciences | DE-SC0006878 |
| Oak Ridge National Laboratory | CNMS2016-109 |
| Lawrence Berkeley National Laboratory | |
| Chemical Sciences, Geosciences, and Biosciences Division |
Keywords
- Accessible surface area
- Diagenesis
- Hydraulic fracturing target
- Microfabric
- Mineralogy
- Point Pleasant Formation
- Porosity
- Utica Shale