Michael E. Hohn

Heterogeneity of Fluvial-Deltaic Reservoirs in the Appalachian Basin: A Case Study from a Lower Mississippian Oil Field in Central West Virginia

Since discovery in 1924, Granny Creek field in central West Virginia has experienced several periods of renewed drilling for oil in a fluvial-deltaic sandstone in the Lower Mississippian Price Formation. Depositional and diagenetic features leading to reservoir heterogeneity include highly variable grain size, thin shale and siltstone beds, and zones containing large quantities of calcite, siderite, or quartz cement. Electrofacies defined through cluster analysis of wireline log responses corresponded approximately to facies observed in core. Three-dimensional models of porosity computed from density logs showed that zones of relatively high porosity were discontinuous across the field. The regression of core permeability on core porosity is statistically significant, and differs for each electrofacies. Zones of high permeability estimated from porosity and electrofacies tend to be discontinuous and aligned roughly north-south. Cumulative oil production varies considerably between adjacent wells, and corresponds very poorly with trends in porosity and permeability. Original oil in place, estimated for each well from reservoir thickness, porosity, water saturation, and an assumed value for drainage radius, is highly variable in the southern part of the field, which is characterized by relatively complex interfingering of electrofacies and similar variability in porosity and permeability.

Uncertainty in coal property valuation in West Virginia: A case study

AbstractInterpolated grids of coal bed thickness are being considered for use in a proposed method for taxation of coal in the state of West Virginia (United States). To assess the origin and magnitude of possible inaccuracies in calculated coal tonnage, we used conditional simulation to generate equiprobable realizations of net coal thickness for two coals on a 7

Stochastic Simulation of Coal Bed Thickness and Economic Decision-Making

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CREATING A GEOLOGIC PLAY BOOK FOR TRENTON-BLACK RIVER APPALACHIAN BASIN EXPLORATION

min topographic quadrangle, and a third coal in a second quadrangle. Coals differed in average thickness and proportion of original coal that had been removed by erosion; all three coals crop out in the study area. Coal tonnage was calculated for each realization and for each interpolated grid for actual and artificial property parcels, and differences were summarized as graphs of percent difference between tonnage calculated from the grid and average tonnage from simulations. Coal in individual parcels was considered minable for valuation purposes if average thickness in each parcel exceeded 30 inches. Results of this study show that over 75% of the parcels are classified correctly as minable or unminable based on interpolation grids of coal bed thickness. Although between 80 and 90% of the tonnages differ by less than 20% between interpolated values and simulated values, a nonlinear conditional bias might exist in estimation of coal tonnage from interpolated thickness, such that tonnage is underestimated where coal is thin, and overestimated where coal is thick. The largest percent differences occur for parcels that are small in area, although because of the small quantities of coal in question, bias is small on an absolute scale for these parcels. For a given parcel size, maximum apparent overestimation of coal tonnage occurs in parcels with an average coal bed thickness near the minable cutoff of 30 in. Conditional bias in tonnage for parcels having a coal thickness exceeding the cutoff by 10 in. or more is constant for two of the three coals studied, and increases slightly with average thickness for the third coal.

Binary Coefficients Redux

The association between constant-sum variables Xiand Xjexpressed as percentages can be calculated as a product-moment correlation between Xiand Xj/(100 − Xi) and a correlation between Xjand Xi/(100 − Xj). An asymmetric, square matrix may be formed from these coefficients, and multivariate analysis performed by two methods: singular value decomposition and canonical decomposition. Either analysis avoids problems in the interpretation of correlation coefficients determined from closed arrays, and provides information about dependencies among the variables beyond that obtained from the usual correlation coefficient between Xiand Xj.Two examples show the canonical decomposition to have the greater usefulness.

Geostatistical Methods for Reservoir Geophysics by Azevedo, L. and Soares, A.

The State of West Virginia (eastern United States) taxes owners of coal that exceeds a specified threshold in thickness under their property. This criterion for minability does not account for uncertainty in the estimation of average coal thickness. A new criterion is proposed that uses conditional simulation to generate multiple realizations of coal thickness in a 7.5 minute quadrangle in West Virginia. From each simulated surface, the average thickness and total coal volume can be computed for each parcel. The total set of simulations is used to determine percentiles of average coal thickness by parcel. The proposed criterion requires that a given percentile of average values exceed the threshold for a parcel to be classified as minable, and therefore subject to taxation. This study shows the effect of criterion, parcel size, regional coal bed thickness, and sample size on the proportion of parcels determined to be minable.

ENHANCING RESERVOIR MANAGEMENT IN THE APPALACHIAN BASIN BY IDENTIFYING TECHNICAL BARRIER AND PREFERRED PRACTICES

Outbreaks of the gypsy moth, Lymantria dispar (L.), occur over large areas, but are difficult to predict. Models used previously to forecast defoliation utilized preseason counts of egg masses in a given stand of trees. Three dimensional indicator kriging is applied to the problem of forecasting local probability of outbreak in each of 6,075 2 km by 2 km cells in the state of Massachusetts, USA. From defoliation data representing about thirty years of records, variography showed a temporal persistence of outbreaks to be about 5 years on the average. An omnidirectional, spatial variogram was computed for each of the years since 1984, and found to be sensitive to the number of cells defoliated. At low densities, spatial variograms approached a pure nugget effect, whereas in years of relatively high densities, defoliated cells were clearly clustered. These observations were used to construct and test a three-dimensional simple indicator kriging estimator that uses two years of observed defoliation prior to the year to be forecast, and estimates of global level of defoliation for selecting a variogram and specifying an estimated frequency of defoliation.

An Evaluation of the Minimum Required Sampling Density of Middle Pennsylvanian Interburdens at a Typical Southern West Virginia Surface Mine; A Preliminary Study: ABSTRACT

The Trenton-Black River Appalachian Basin Research Consortium has made significant progress toward their goal of producing a geologic play book for the Trenton-Black River gas play. The final product will include a resource assessment model of Trenton-Black River reservoirs; possible fairways within which to concentrate further studies and seismic programs; and a model for the origin of Trenton-Black River hydrothermal dolomite reservoirs. All seismic data available to the consortium have been examined. Synthetic seismograms constructed for specific wells have enabled researchers to correlate the tops of 15 stratigraphic units determined from well logs to seismic profiles in New York, Pennsylvania, Ohio, West Virginia and Kentucky. In addition, three surfaces for the area have been depth converted, gridded and mapped. A 16-layer velocity model has been developed to help constrain time-to-depth conversions. Considerable progress was made in fault trend delineation and seismic-stratigraphic correlation within the project area. Isopach maps and a network of gamma-ray cross sections supplemented with core descriptions allowed researchers to more clearly define the architecture of the basin during Middle and Late Ordovician time, the control of basin architecture on carbonate and shale deposition and eventually, the location of reservoirs in Trenton Limestone and Black River Group carbonates. The basin architecture itself may be structurally controlled, and this fault-related structural control along platform margins influenced the formation of hydrothermal dolomite reservoirs in original limestone facies deposited in high energy environments. This resulted in productive trends along the northwest margin of the Trenton platform in Ohio. The continuation of this platform margin into New York should provide further areas with good exploration potential. The focus of the petrographic study shifted from cataloging a broad spectrum of carbonate rocks that occur in the Trenton-Black River interval to delineation of regional limestone diagenesis in the basin. A consistent basin-wide pattern of marine and burial diagenesis that resulted in relatively low porosity and permeability in the subtidal facies of these rocks has been documented across the study area. Six diagenetic stages have been recognized: four marine diagenesis stages and two burial diagenesis stages. This dominance of extensive marine and burial diagenesis yielded rocks with low reservoir potential, with the exception of fractured limestone and dolostone reservoirs. Commercial amounts of porosity, permeability and petroleum accumulation appear to be restricted to areas where secondary porosity developed in association with hydrothermal fluid flow along faults and fractures related to basement tectonics. A broad range of geochemical and fluid inclusion analyses have aided in a better understanding of the origin of the dolomites in the Trenton and Black River Groups over the study area. The results of these analyses support a hydrothermal origin for all of the various dolomite types found to date. The fluid inclusion data suggest that all of the dolomite types analyzed formed from hot saline brines. The dolomite is enriched in iron and manganese, which supports a subsurface origin for the dolomitizing brine. Strontium isotope data suggest that the fluids passed through basement rocks or immature siliciclastic rocks prior to forming the dolomites. All of these data suggest a hot, subsurface origin for the dolomites. The project database continued to be redesigned, developed and deployed. Production data are being reformatted for standard relational database management system requirements. Use of the project intranet by industry partners essentially doubled during the reporting period.