ow-permeability ("tight") reservoir sandstones of the lower Missourian Cleveland formation produced more than 435 billion cubic feet (Bcf) of natural gas through December 1990, mostly from Ochiltree and Lipscomb Counties in the northeastern Texas Panhandle. Although large-scale gas production started in1956, the regional stratigraphic, depositional, and structural setting of the Cleveland is poorly known.

Dipmeter analyses performed within McAllen Ranch field, Hidalgo County, South Texas, proved useful in finding reserves of natural gas. McAllen Ranch field produces from the Oligocene Vicksburg Formation on the downthrown, east block of a listric growth fault that merges with a flatlying glide plane beneath the field. This study concentrated on the Vicksburg S reservoir in a 5-mi2 (13-km2) area of the field (the B area), where a dense array of 15 dipmeter logs and a three-dimensional seismic survey were available.

An active diapir forcefully intrudes its overburden, driven by diapir pressure that overcomes the resistance of the overburden strength. Possible causes of the driving pressure are differential loading of the source layer and a density contrast with the overburden. Resisting forces derive from the mass of the roof block and resistance to the faulting and folding that accommodate the intrusion.