Predictive Model for Fracture Distribution and Intensity in Sandstone and Carbonate Reservoirs, Wertz and Lost Soldier Fields, Wyoming

Holly L. Harrison, Joan Tilden

The Tensleep Sandstone and Madison carbonate reservoirs at Wertz and Lost Soldier fields, southern Wyoming, were the subject of a fracture distribution study as part of a tertiary development study. A fracture classification scheme for the reservoirs was developed, and foot-by-foot fracture description of 15 cores throughout the two fields were generated.

The core fracture classifications and descriptions were digitized for computer use. A computer-generated second-derivative map of the Tensleep structure accurately reflected fracture distribution as described from cores in both the sandstone and carbonate reservoirs. Computer-generated crossplots of number of fractures per foot vs. a variety of petrophysical rock parameters identified structural position and lithology as the key factors governing fracture distribution and intensity in the Tensleep and Madison reservoirs. The Schlumberger long-spaced sonic composite fracture identification log (CFIL) was compared to the quantitative core fracture descriptions. Once calibrated to core data, the CFIL showed excellent agreement with the foot-by-foot core fracture descriptions in both the ensleep and Madison reservoirs, and can be used to identify field-wide variations in fracture distribution.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.