ABSTRACT

Predicting the production from wells drilled in certain Smackover reservoirs is often difficult. Production history from the field, core analysis and log data have not always proved to be helpful.

The Smackover reservoirs for which log interpretation is difficult fall into two categories. The first is oolitic limestone characterized by low resistivity, moderate porosity (10-20%) and permeability (100-500 md). High water saturation calculated from logs does not necessarily preclude hydrocarbon production. The second is oomoldic limestone typically having high resistivity, high porosity (20-35%) and low permeability (< 100 md). Although log interpretation indicates low water saturation, no hydrocarbons are produced.

Cores from the oolitic, low resistivity intervals were studied to evaluate the relationships now employed for understanding and predicting production. The investigation included: 1) determination of the single textural component "W," the "m" and "n" exponents (known as the cementation and saturation exponents in Archie's equation); 2) evaluation of the rock texture by scanning electron microscopy and thin sections; and 3) laboratory determination of density, porosity and permeability.

The results of the rock physics investigation support the empirical relationships established and provide data for improved interpretation. Rock physics analysis and textural observations on the cores show interesting possible-relationships between rock texture and parameters of the Archie relationship.