Stimulation of Low-Permeability Gas Formations by Massive Hydraulic Fracturing A Study of Well Performance

Abstract

Gidley, J.L., SPE-AIME, Exxon Co. U.S.A. Mutti, D.H., SPE-AIME, Exxon Co. U.S.A. Nierode, D.E., SPE-AIME, Exxon Production Research CO. Kehn, D.M., SPE-AIME, Exxon Production Research Co. Muecke, T.W., SPE-AIME, Exxon Production Research Co. The performance of several wells completed in tight gas sands that have been stimulated by massive hydraulic fracturing is compared with predicted performance. Results agree when the net sand thickness available in the performance. Results agree when the net sand thickness available in the wellbore of the fractured wells is reduced by a factor of 4. Sand discontinuity is used to explain this result. Introduction Even though gas has been produced in limited quantities from tight gas sands in the Rocky Mountain area for the last several decades. development of this area as a significant source of gas production has occurred only since the early 1970's. Efforts intensified with the growing awareness of the domestic energy shortage. The Federal Power Commission estimates that about 600 Tcf gas reserves can be found in this area. A National Gas Survey indicates that these reserves can be exploited. Interest in the area has revived. Recent increases in federally regulated interstate natural gas prices have provided an economic incentive for developing these provided an economic incentive for developing these reserves. Both nuclear stimulation and massive hydraulic fracturing (MHF) have been suggested as methods for producing this latent gas. Fig. 1 shows the geographical producing this latent gas. Fig. 1 shows the geographical locations of several tests of both methods and also identifies the principal geologic basins of interest. This paper does not deal with the results of nuclear stimulation experiments because these results are covered elsewhere. Applications for that technology are now dormant. Rather, we examine the results of several MHF treatments in the area to see how the production rate from fractured wells compares with predicted performance. The size and calculated geometry of the fracture and known reservoir properties of the sands are used for these comparisons. With a few noteworthy exceptions, the MHF results for the Mesaverde and Fort Union sands (the major gas sands in the Rocky Mountain area) have been largely disappointing. Although the problem originally was attributed to certain deficiencies problem originally was attributed to certain deficiencies in the hydraulic fracturing technique, it now appears that this response is inherent in the nature of the formations. This study was not limited to Exxon Co. U.S.A. wells alone, since our involvement in the Rocky Mountain area has been minimal. We also looked at the performance of other operator's wells. For the latter wells, most data were obtained from trade journals, publications of the federal government (since most of the wells are on federal leases), local newspaper articles, or other sources. Some of these companies have not been contacted directly regarding the data used on their wells or this analysis of well performance. Other companies are mentioned in this paper performance. Other companies are mentioned in this paper for well identification only, and no concurrence on their part is implied with the conclusions drawn. part is implied with the conclusions drawn. Type of Treatments Examined The term massive hydraulic fracturing used here refers simply to very large fracturing treatments, generally an order of magnitude larger than conventional fracturing procedures. Typically, an MHF involves more than procedures. Typically, an MHF involves more than 100,000 gal fracturing fluid and more than 200,000 lb sand. JPT P. 525