Early development of Eagle Ford Shale (EFS) indicated the reservoir was relatively sweet, typically producing H2S in low concentrations (<1%). However in McMullen Co. TX, wells with high concentration (>4%) are found. Mapping raw untreated H2S gas concentration shows a direct correlation to salt domes and subsequent deep faulting. The enigma has been high H2S wells offset by low H2S wells, not associated with salt domes or faulting. Micro-seismic and re-processed seismic data revealed that deep faults do intersect these wellbores. Mapping of these deep features allows for the prediction of areas with high H2S.
An economic model was developed, based on the expected H2S concentration and production forecast, that is capable of directing the long term drilling and completions strategy as well as to provide expectations for use in the construction of facilities and selection of H2S treatment options. The drilling and completion strategy minimized the amount of H2S that will be encountered and the optimization of facilities reduces operating inefficiencies and OPEX and CAPEX outlays.