Quantitative determination of lithofacies using geophysical inverse theory, drinkard unit, Permian Basin, Lea County, southeast New Mexico

The determination of the correlation between the petrophysical data and core data is essential in the determination of reservoir rock properties. The goal of this study is to design a computer algorithm, which will use the geophysical inverse theory to deduce different reservoir facies from well log responses by utilizing statistical relationships between the well logs and core derived lithofacies.; In most oil and gas fields only a minority of the wells are cored. As a result, determination of reservoir rock properties is mainly dependent on the interpretation of geophysical log data. An objective approach to analyze well log data to determine the rock properties would speed up the interpretive process and would also enable the researcher to correlate information between wells and incorporate a priori knowledge into their interpretation.; Detailed core and petrographical analysis was conducted as the first step in establishing statistical relationships of lithological data four cored wells. Secondly, a valid forward model, which is a requirement in any successful inversion process, was constructed by the usage of mathematical formulation of well logs available and the petrographical data obtained from cores, Well log types used for this study include Neutron Porosity, Bulk Density, Interval Transit Time, and Lithodensity logs. A unity constraint was also used as a supplementary log data. Thirdly, an inversion method, which can incorporate the results of core analysis and petrographical information as potential constrains in the inversion itself was determined.; The facies observed between wells in a given oil and gas field are related to another, therefore, use the four cored wells with depositional facies control to determine if results from one well can provide lithofacies information in the remaining wells. An inversion algorithm using a priori geologic information was tested on four cored wells. Up to eleven lithofacies were successfully obtained by the inversion.; Because, only a small number of wells in a given field are ever cored, an approach that uses depositional facies knowledge from those few cored wells to refine the interpretation of the remaining wells would improve the correlation efforts and provide the oil industry a better understanding of the producing reservoir and ultimately improve recovery of hydrocarbons.