COMPARISON OF POTENTIOMETRIC SURFACES FROM COMBINED WATER WELL AND OIL WELL DATA IN THE MIDCONTINENT OF THE UNITED STATES

Understanding formation pressure on a regional scale is extremely valuable to the oil and gas industry and is an emerging area of interest in carbon dioxide sequestration. Historically, hydrologists have defined potentiometric surfaces using measured hydraulic-head values in water wells from aquifers to map flow within a formation. Down-dip, the oil and gas industry is also interested in the formation pressures of many of the same geologic formations deeper in the subsurface for the purpose of hydrocarbon recovery. In conventional oil and gas basins, drillstem tests (DSTs) are conducted to record formation pressure for a given depth interval in a well. These DST measurements can be used to calculate hydraulic head values in deep hydrocarbon-bearing formations where water wells do not exist. The resulting calculated hydraulic head values are used to create a potentiometric surface in the same manner as hydraulic head measurements from water wells.

We have created a set of potentiometric surfaces for Mesozoic and Paleozoic stratigraphic units within the Denver Basin and Anadarko Basin in the Midcontinent of the United States by combining these two sources of data. In describing the stages of the methodology, we will discuss the steps used to create the potentiometric surfaces and outline the challenges and uncertainty that have been identified in the process. Error analysis of key steps is included to account for variations in formation salinity and overall user interpretation of the noisy datasets. The end result is a comparison of potentiometric surfaces for each stratigraphic unit including the area of discharge and the connectivity of each unit on a regional scale.