A Case History for Massive Hydraulic Fracturing the Cotton Valley Lime Matrix, Fallon and Personville Fields

Summary This report summarizes the results of an active stimulation program on the Cotton Valley Lime as evaluated using reservoir production and pressure transient data. Using standard economic parameters and reservoir permeabilities determined by history matching, a detailed study was made to determine the well spacing and fracture length radius necessary for optimum development of the Fallon and North Personville fields. Introduction Considerable emphasis has been placed in recent years on recovering gas from "tight-gas" basins. One step that shows promise for unlocking tight gas is massive hydraulic fracturing (MHF). A case in point is the evolution of the stimulation in the Cotton Valley Lime at Fallon and North Personville fields, about 10 miles southeast of Mexia in Limestone County, TX (Fig. 1).The Jurassic Cotton Valley group on the west flank of the East Texas basin generally consists of a succession of about 1,000 ft of terrestrial and marine sands and shales, 800 ft of dark (Bossier) shale, and 300 to 500 ft of limestone at the bottom known as the Cotton Valley Lime or Haynesville. The group covers more than 250,000 sq miles in the East Texas basin and adjacent parts of Louisiana and southeast Arkansas.The Cotton Valley Lime in the Fallon and North Personville area has been a known gas area since its discovery in 1969. However, its poor permeability pay at a depth of about 11,000 ft had produced at rates too low for commercial development under the price schedules and technology of the past decade. Due to fracture porosity, beginning rates were moderately good (1 to 4 MMcf/D), but the natural fracture system was not sufficient to maintain the high rates of flow; consequently, the rates dropped to 0.200 to 0.500 MMcf/D in less than 2 years.Lately, advances in stimulation technology and improved economic incentives renewed interest in this area. Conventional acid stimulations and small fracturing jobs brought some improvement. Bigger fracturing jobs brought further improvement, but MHF appears worthwhile.These are the objectives of this report:1. Document the evolution of stimulation technology of the Cotton Valley Lime at the Fallon and North Personville fields.2. Using a computer reservoir simulator, history match the production and pressure transient data of the Muse No. 1 well before and after MHF and determine the uniqueness of this solution.3. History match the production of the Muse-Duke No. 1 after a super-MHF treatment.4. Optimize the development of the Cotton Valley Lime reservoir with respect to fracture length and well density using reservoir data and economic guidelines.5. Document the design of a super-MHF job (see Appendix). Reservoir Characteristics Rock Parameters The Cotton Valley Lime formation is generally gray, massive, oolitic to pistolitic, and finely crystalline to micritic. The better porosities appear to be related to the oolitic zones, ranging from 2 to 12% with some local thin zones of 14%. JPT P. 229^