Successful exploration in a challenging frontier

Abstract

Of the many hydrocarbon plays available in Nevada, the Mississippian Chainman Shale resource play may offer the greatest reserve potential. It contains world class source rocks and solution enhanced fractured carbonate reservoirs. These reservoirs have high flow rates and when combined with the commonly present active freshwater drive produce great economics. So why then has the wildcat success rate been so dismal? It seems that the exploration programs commonly used in Nevada where developed elsewhere where the geology is vastly different. Nevada has been affected by multiple compressional tectonic events in the Paleozoic and Mesozoic, followed by the more recent Tertiary extensional Basin and Range event. For success, an exploration program must be designed for Nevada. For pre-Tertiary targets, seismic is expensive and rarely gives usable data beneath the Tertiary basins because of the complex discontinuous structure in the pre-Tertiary strata. Detailed gravity data is much less expensive and provides good definition of the morphology of the bottom of the Tertiary basins. When interpreted with surface geology, detailed gravity data provides numerous prospective leads. The critical element for Nevada exploration is to determine which of the abundant prospective leads is a trap containing hydrocarbons. Nevada production experience offers data germane to a solution for the problem. First, much of the oil produced in Nevada is free of light hydrocarbons. Second, many of the oil accumulations have a tar top seal of degraded hydrocarbons. Both of these suggest that significant micro-seepage has taken place. Such micro-seepage generally produces chemical changes in the soil at the surface above the seep. There is generally little or no agricultural or other surface disturbance in Nevada, suggesting that surface detection techniques will be successful tools when properly used. Combining detailed gravity with a combination of surface detection techniques offers an exploration program designed for Nevada geology. A comprehensive exploration program for conventional vertically-drilled prospects in the Chainman Shale resource system will be presented with examples.

AAPG Datapages/Search and Discovery Article #90266 © 2016 AAPG Pacific Section and Rocky Mountain Section Joint Meeting, Las Vegas, Nevada, October 2-5, 2016