Salt dissolution and surface subsidence in central Kansas: A seismic investigation of the anthropogenic and natural origin models

Abstract

Gradual subsidence in the Punkin Center study area, northeast Reno County, Kansas, has resulted in ponding of surface waters, abandonment of at least one oil well, and damage to county roads. Because the Punkin Center area is within the Burrton oil field and is underlain by the Hutchinson Salt Member, surface subsidence historically has been attributed to salt dissolution of anthropogenic origin. Subsidence that occurred significant distances from any known well sites has been attributed to unrecorded abandoned wells or complex asymmetric patterns of salt dissolution that originated at a drillhole. To ascertain the validity of the widely accepted anthropogenic salt‐dissolution model, a 4-km seismic reflection profile was acquired along an east‐west‐oriented county road adjacent to an abandoned oil well. The expectation was that the residual Hutchinson Salt Member would be anomalously thin where maximum recorded surface subsidence occurred and thicker elsewhere. Contrary to expectations, the residual Hutchinson Salt Member is relatively thick (20–30 m) below areas of significant recent surface subsidence. There is no evidence of recent surface subsidence at those locations along the seismic profile where the rock salt has been totally leached. At these sites dissolution and subsidence is interpreted to predate European settlement in Kansas and to be of natural origin. The presence of dissolution and subsidence features related to natural processes has implications for developing an understanding of the potentially complex relationship between anthropogenic activities and pre‐existing geologic conditions. Sinkhole development is apparently a natural and expected process along an irregular salt dissolution front. The geometry of this front may be influenced strongly by geologic factors (e.g., fracture patterns and facies distribution). The results are that not all modern sinkhole development has a clear‐cut anthropogenic cause, and the potential for adverse impact resulting from anthropogenic activities will be influenced strongly by pre‐existing geologic conditions. Efficient management decisions along the dissolution front related to well location and well‐site practices should take into account natural processes that previously have and will continue to have an effect on salt dissolution and surface subsidence.