Kevin W. Schmidt¹, Louis P. Goldstein¹, David W. Holmes¹, Mark A. Dablain¹, Charles D. Sharp¹, Terry L. Jensen¹

(1) Pioneer Natural Resources, Irving, TX

ABSTRACT: Evolution of the Pawnee Field Horizontal Development Program, Edwards Formation, south Texas

The lower Cretaceous Edwards Formation associated with the Pawnee Field in south Texas has historically been developed through the drilling of vertical well-bores. However, lateral and vertical reservoir heterogeneity suggested the field held significant potential for additional reserves through development by horizontal drilling.

Since 1996, fifteen horizontal wells have been drilled in the Edwards reef complex with varying results; twelve of the fifteen wells have been completed since November 1999. Before and during this on-going development program, a multi-disciplined approach was used to integrate geophysical and geological interpretations, core analysis, reservoir engineering data, and drilling and production information to construct a coherent but evolving picture of the Edwards reservoir.

Early attempts were made to optimize horizontal wellbore orientation and targeting with emphasis on porosity distribution. A mix of fracturing and porosity development had always been considered critical to successful production in Pawnee Field, with earlier horizontal wells targeting the highest available porosity. Porosity-based maps, however, exhibited little correlation to recoverable gas volumes. Study of the available cores indicated that the best porosity-permeability relationship was found in the reef-detritus grainstone facies, and that fractures played a much more significant role than previously thought. Subsequent attention shifted away from porosity toward fracturing and facies distribution as the key factors impacting production. Current activity focuses on mapping reservoir facies and characterizing the orientation and density of open fractures.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado