Analysis of the Success of Cavity Completions in the Fairway Zone of the San Juan Basin

R. Muthukumarappan, Rudy E. Rogers, S. Dana Weida

Wells completed by the openhole cavity technique in the Fruitland formation of the fairway zone in the San Juan basin have demonstrated gas production rates nearly ten times greater than production rates from wells completed by fracturing in the same area, but expensive trial and error selection of wells to cavity complete outside the fairway and in other basins must be made.

Data from numerous wells were obtained from four companies active in the basin. Five parameters of in-situ stress, bottom-hole pressure, ash content, volatile matter, and depth to the top of the Fruitland coalseams were statistically ranked by their importance to the success of cavity completion techniques, and these five parameters were contoured using the "Surfer" software. From the resulting contours, boundaries of fairway zones similar to that of the San Juan basin can now be defined in unexplored basins.

This study is the first to assimilate enough minimum in-situ stress data in the San Juan basin to statistically correlate with production rates. The statistical analysis shows minimum in-situ stress to be the most important parameter of the five studied for successful cavity completions. A threshold minimum in-situ stress between 2080-2359 psi is required if other parameters of the study are satisfactory.

The study is important for coalbed methane development around the world where coalseams as successful as the San Juan fairway are sought for the application of cavity completions.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995