Fracturing and Testing Case Study of Paludal, Tight, Lenticular Gas Sands

This paper is a case study of the stimulation and testing of tight lenticular sands in the paludal interval of the Mesaverde Group in the Piceance basin as DOE's Multiwell Experiment site in Colorado. Prestimulation data acquired include (1) geologic studies which delineate the size and shape of the lenses, (2) detailed core reservoir/rock property data, (3) stress test data showing the vertical distribution of stress throgh the interval, (4) drawdown, buildup, and interference tests which provide in situ reservoir properties, and (5) laboratory data on frac fluid invasion and damage. Stimulation of the zone was conducted in two phases. The first phase consisted of steprate/flowback tests and two minifracs in which pre-frac design information was obtained. The main stimulation was the second phase and it consisted of 75,000 gal (284 m/sup 3/) of cross-linked HPG and 193,000 lbs. (87,545 kg) of sand. Bottomhole pressure and temperature, as well as all surface data, were obtained and borehole geophones were used for fracture diagnostics. Detailed pre-frac, between-frac, and post-frac well test programs were conducted in conjunction with the stimulation. Severe cleanup problems and remedial actions are documented. The analyses and diagnostics give some indication of fracture geometry in this lenticular environment.more » Complications such as high treatment pressures and frac-fluid damage are detailed. Gas production was decreased (at least over short test periods) by both phases of the treatment; this was probably due to damage to the natural fractures which did not have sufficient time to clean up. 14 references, 10 figures, 1 table.« less