The Chocolate Bayou Field is located 25 miles south of Houston, in southeast Brazoria County, Texas. Discovered in 1938, the field has produced over 2 trillion cubic feet of natural gas and 65 million barrels of oil from approximately 30 sands and 300 wellbores. The majority of the production is from the sands of the upper and middle Frio (Oligocene) section. Accumulation is found on structural highs on both the downthrown and upthrown side of a major basinward growth fault.

A 3-D seismic survey was conducted over the field in 1988 in an effort to locate bypassed reserves. Interpretation of the data revealed an unexpected paleostructure associated with a buried and previously undetected counter-regional fault located almost three miles south of the structural crest at the Upper Frio level. Detailed structural and isochron mapping with adequate depth conversions indicated that the structure was prospective for trapping in the lower Frio sands which were well developed but wet under the Upper Frio structural crest.

Although the feature was located on the absolute edge of the survey the data was adequate to locate two wells which have now been completed in the lower Frio section. The sands range in thickness from 65 to 115 feet of net pa with porosities from 27 to 30%, with sustained production rates in excess of 10,000 million cubic feet of gas and 140 barrels of oil per day per completion.

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