ABSTRACT

Sour Lake is a large piercement salt dome located in southern Hardin County, Texas. Recent deformation of the cellar and wellhead of one of the salt cavern storage wells initiated a geologic investigation into the cause of the deformation and its future impact. Unlike many of the other Gulf Coast salt diapirs that have a flat or inclined upper salt surface, the upper surface of the salt at Sour Lake is strongly domed with over 1000ft of relief. The geologic investigation showed that the diapir has maintained a near-surface position since at least Yegua time and appears to be characterized by a passive or down-building stage. However, the central area of the diapir has been an area of active uplift since late Frio time resulting in a complex graben system forming over the central area of the dome. The cause of the 1929 sinkhole occurrence at Sour Lake was re-evaluated and provided the basis for mapping the changes in ground level between 1923 and 1965. These changes in elevation show areas of uplift and subsidence that correspond to the underlying graben system. In addition to being located in the area of active uplift, the storage well experiencing the deformation is also located on a smaller and more active area of salt uplift (a salt spine). Since the late 1960's, this spine has begun moving and has resulted in the over-pressuring of the caprock and adjacent sands. Active salt movement at Sour Lake has resulted in uplift and extension of the overlying strata and has produced surface subsidence.