The geology of the Silsbee Oil and Gas Field, Hardin County, Texas

The Silsbee Oil and Gas Field is located in northeastern Hardin County, about twenty-six miles north of Beaumont, Texas. The surface formation is the Lissie of Pleistocene Age. Oil and gas production is being obtained from sands of the Claiborne group of the Eocene. The deepest well so far drilled penetrated 617 feet of the Wilcox formation, but no production resulted from that formation. The structure was discovered by geophysics. The first indication was a torsion balance minimum which was interpreted to be the result of a deep-seated salt dome. A reflection seismograph survey followed which confirmed the presence of the structure but shifted its location about two miles to the west of the position indicated by the torsion balance. Subsequent drilling has shown the structure very nearly to coincide with the torsion balance anomaly. The Silsbee structure is a strike fold associated with a down-toward-the-Gulf strike fault; closure on the down-thrown side. Isopach studies indicate the structure was present and probably growing during deposition of the Yegua sands, which form the petroleum reservoirs in the field. This was likely an important factor in the accumulation of oil and gas in these sands. Structural movement is shown following the close of the Yegua cycle of deposition and prior to Vicksburg deposition. Following Vicksburg deposition, a period relative quiesence ensued which lasted until after the deposition of the Catahoula formation of the Miocene, There is evidence of movement since deposition of this formation. The origin of the Silsbee structure presents an interesting question as to whether it may be ascribed solely to normal tension or "slump" faulting, or whether it is the result of the positive uplift of a deep- seated salt dome. The writer is of the opinion that the evidence indicates salt movement was at least a conttibuting factor in the forming of the structure.