Role of Petroleum Systems Modeling in Appraising the Point Pleasant Play, Eastern Ohio
Crews, Steven G.; Guthrie, John M.; Ahmed, Khurrum; Vines, John A.
Petroleum systems modeling techniques that are widely used to risk charge and estimate fluid properties and volumes in conventional exploration are also proving useful in appraising unconventional plays. Crucial fluid property questions can be addressed by petroleum systems models because the fluids are controlled or strongly influenced by key model elements such as source rock properties and thermal maturity.
This study is a regional 3-D burial history, thermal maturity, generation and expulsion model of the Ordovician Point Pleasant unit in the subsurface of eastern Ohio. It was undertaken to help an unconventional appraisal team evaluate acreage distributed over a wide area of the Point Pleasant play; specifically, to predict fluid composition including oil vs. gas, GOR, and gas wetness/condensate yield. The model covers approximately 146,000 km² (36 million acres) and comprises 10 stratigraphic layers, spanning Cambrian-Holocene time. Two key aspects of this model are: (1) estimating missing section on the surface unconformity, and (2) simulating expulsion and retention of hydrocarbons as the source rock was buried, then partially exhumed.
A significant surface unconformity is indicated by the regional outcrop pattern and the observed compaction and thermal maturity of exposed rock. In particular, upper Pennsylvanian coals in the study area yield Ro values of 0.59-0.96%. Modeling deposition and erosion associated with this unconformity is key to predicting the state of maturity of the source rock. We calibrated our estimates of the missing section by comparing model-predicted and measured values of three data sets: (1) surface coal vitrinite reflectance; (2) maturity of oil reservoired in the overlying Clinton Sandstone; and (3) present-day HI values in the Point Pleasant. The thickness of missing section is estimated to exceed 4 km in the dry gas portion of the play in eastern Ohio.
Our expulsion-retention simulation considers sorption and pore saturation thresholds, and inorganic (matrix) and organic (kerogen) porosity, among other factors. However, all of these parameters are difficult to constrain a priori. We therefore take the approach of iteratively adjusting them to calibrate the GOR predictions of our model to observed cumulative gas and liquids production data.
This "bottom-up" approach is thus calibrated to produced fluids data while also allowing us to predict fluid properties far away from existing production.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013