Analysis of 3-D Ground-Penetrating Radar (GPR) Data for Reservoir Characterization of Rudist Mounds, Central Texas

Abstract

We analyzed 3-D ground-penetrating radar (GPR) data from the Lower Cretaceous shallow carbonate environment in Lake Georgetown, Williamson County, Central Texas to characterize the rudist mounds that form an important hydrocarbon reservoir in the area. The GPR survey covers a volume with a surface area of 82 ？ 93 m and depth of about 17 m. The data set consists of 83 inlines and 94 crosslines with a line spacing of 1 m. Data processing included velocity analysis, based on six CDP gathers, and poststack Kirchhoff time migration. The cores from the engineering well drilled by the United States Army Corps of Engineers from the study area are dominated by carbonates with a wide range of porosity and density. We identified five rudist mounds, characterized by strong top reflections with high radar coherency. The rudist mounds are 5 ？ 20 m wide and 1 ？ 3.5 m high, comparable to those exposed in outcrops in the area. The inversion using the pseudo log, constructed from the porosity and density descriptions in the core report, shows that the porosity decreases toward the crestal part of the rudist mounds, suggesting decreased dolomitization.