Abstract

One of the most active areas of current drilling activity in the Permian basin is in Terrell County, Texas. Although the Ellenburger, Fusselman, and Strawn formations offer tremendous gas potential for deep drilling, the Wolfcamp sandstones present a shallow objective for natural gas exploration. With sediment accumulations on the order of 12,000 ft, the shales of the Wolfcamp provide the source of the hydrocarbons and the Wolfcamp sandstones provide the reservoir rock. The typical Wolfcamp sandstones have low porosity and very low permeability. The better producing gas wells are those that penetrate naturally-fractured Wolfcamp sandstones. Unless the sandstone package contains natural fractures, the gas production will be uneconomical. For this reason it is most important to recognize the presence of fracturing in order to assess the economic potential of the well before setting production casing. One way to detect and evaluate the presence of fractures is with wireline well logs. The presence of fractures is detected on these well logs because of the anomalies produced by fracturing that effect the gamma ray, density, temperature, and sonic measurements. This paper evaluates the presence of natural fractures as reflected by wireline well log measurements and compares these results to the production records of the subject wells.