Northeast Thompsonville Field, South Texas: Key to Future Exploration for Downdip Wilcox Production?

Abstract

The general configuration of the Northeast Thompsonville field structure, Jim Hogg and Webb Counties, south Texas, was well defined by detail seismic surveys conducted in the area prior to the drilling of the first well. Early drilling proved that the major down-to-the-east fault controlling accumulation on the anticline dips 27°. This invalidated certain assumptions that were made regarding the strike of the fault during the early development of the field. As the field was developed, the true alignment and dip of the fault were established, and it was found that the producing Hinnant Sand (Wilcox Formation) in structurally low wells has much lower permeability than in the structurally high wells. These and other data indicate to the writer that the Hinnant Sand was n offshore bar. The possibility exists that the low-angle fault is related directly to the slip face (seaward side) of this bar; this might explain the absence of hydrocarbon accumulations on the downthrown sides of certain Wilcox faults along this trend. Another interesting aspect of the study is the evolution of ideas on the structure of the area. Figure 1 is the structural interpretation before the prospect was drilled; Figure 2 is the interpretation after the field discovery; and Figure 3 is the latest interpretation.