CHARACTERIZATION OF HYDROSTRATIGRAPHIC UNITS IN THE NEOGENE SEQUENCE OF SOUTHWEST KANSAS BASED ON DRILLING RECORDS

This research was undertaken to use drilling records to characterize the distribution of lithology and the permeable fraction of the High Plains aquifer by means of various interpolation and geostatistical methods, evaluate differences between approximations, and determine the most effective method for representing subsurface heterogeneity.

Drilling records comprise the most abundant source of information for hydrostratigraphic characterization of the Neogene sequence in southwestern Kansas. A relational database of carefully-screened drilling records was used to consistently translate material descriptions into lithologic terminology, quantify the permeable thickness and fraction of material within heterogeneous deposits, and determine volumetric proportions of lithology. Conditional rules were applied to translate descriptions from drilling records into 62 lithologic categories.

The project database included 4,161 test holes and production wells drilled by water-well contractors and test holes drilled for research programs by the Kansas and U.S. Geological Surveys. Various geostatistical and interpolation techniques were used to estimate the 3d distribution of permeable units. To examine and characterize subsurface heterogeneity, drilling records across the study area were analyzed using various geostatistical approaches and compared with sample logs prepared in the field and from KGS bulletins.

The majority of deposits within the Neogene sequence are in the 36% to 60% relative permeability range. Permeable units vary vertically and laterally, and alternating fining upward and downward patterns are present within the sequence. Increases in permeable fraction generally correspond to increases in total permeable thickness. Permeable thickness is greatest along the axis of a southeast-trending paleovalley and in bedrock lows.

Complex depositional processes are reflected in the distribution of lithology. Detailed appoximations of lithology reveal the spatial distribution of permeable units and increases understanding of the High Plains hydrostratigraphic framework. Data contained in the drilling records are a viable, abundant source of information to supplement subsurface characterization.