Case Study of a Stimulation Experiment in a Fluvial, Tight-Sandstone Gas Reservoir (includes associated papers 23475 and 23567 )
- Norman R. Warpinski (Sandia Natl. Laboratories) | Paul T. Branagan (CER Corp.) | Allan R. Sattler (Sandia Natl. Laboratories) | Craig L. Cipolla (CER Corp.) | John C. Lorenz (Sandia Natl. Laboratories) | B.J. Thorne (Sandia Natl. Laboratories)
- Document ID
- Society of Petroleum Engineers
- SPE Production Engineering
- Publication Date
- November 1990
- Document Type
- Journal Paper
- 403 - 410
- 1990. Society of Petroleum Engineers
- 2.4.3 Sand/Solids Control, 5.8.6 Naturally Fractured Reservoir, 2.5.1 Fracture design and containment, 2.2.2 Perforating, 5.5.8 History Matching, 3 Production and Well Operations, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 2.5.2 Fracturing Materials (Fluids, Proppant), 4.1.2 Separation and Treating, 5.1.3 Sedimentology, 5.4.2 Gas Injection Methods, 5.8.1 Tight Gas, 4.6 Natural Gas, 4.3.1 Hydrates, 5.6.4 Drillstem/Well Testing, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 4.1.5 Processing Equipment, 1.2.3 Rock properties, 5.6.1 Open hole/cased hole log analysis, 1.6.9 Coring, Fishing
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A successful stimulation experiment was conducted in a fluvial sandstone of the Mesaverde formation at the U.S. DOE's Multiwell Experiment(MWX) Site in the Piceance basin of Colorado. The stimulation experiment consisted of stress tests, a three-well prefracture interference test, step-rate/flowback tests, a minifracture, a full stimulation treatment, borehole geophone diagnostics during fracturing, and a postfracture interference test.
The DOE has sponsored research in unconventional gas resources (including tight sandstones, Devonian shales, and hydrates) for many years. In the western U.S., large resources of natural gas have been identified in tight sandstones in several basins; for example, the U.S. Geological Survey estimates that 420 Tcf [12x10(12) m3] of gas is contained in the Piceance basin of western Colorado and that 4,970 Tcf [140x 1012 m3] is in the Greater Green River basin of Wyoming. While only small fractions of these amounts are likely to be recovered, the resource base is so large that continuing research is warranted. From 1981 to 1988, the primary DOE research facility for tight-sandstone experiments has been the MWX, conducted at a site in the Piceance basin near Rifle in west-central Colorado.
The sandstone lenses found at the MWX site are anisotropically naturally fractured with matrix permeabilities of 0.1 to 2 mu d and well-test permeabilities of 10 to 50 mu d. The stress orientation is such that the hydraulic fractures parallel the primary natural fractures, making stimulation of these zones and exploitation of the natural fracture system difficult. Results from documented experiments in this basin appear to corroborate these findings. The depositional environment has been found to be a primary controlling factor of lens sizes and heterogeneities within lenses. The reservoir sizes and the anisotropic nature of the permeability system also have important implications for the size and type of stimulation treatments. The natural fractures, which are very narrow, are easily damaged by fracturing treatments. Treatments have shown a propensity for early screenouts. This tendency has made obtaining maximum treatment lengths difficult and probably has increased damage to the natural fractures owing to the elevated screenout pressures. This early screenout syndrome is now interpreted to be a result of a dual leak off phenomenon that occurs above a threshold pressure. Leakoff increases by as much as a factor of 50 above this critical threshold.
With these factors for perspective, we have conducted testing and stimulation experiments in the fluvial interval. This paper discusses the results of work in one lens, the fluvial Sandstone E.
The MWX field laboratory consists of three closely spaced wells (Wells MWX-1, MWX-2, and MWX-3) arranged in a triangle with spacings of 115 to 215 ft [35 to 66 m] at depth. Well depths are 8,350, 8,300, and 7,565 ft[2545, 2530, and 2306 m], while the Mesaverde at this site is found from 4,100 to 8,300 ft [1250 to 2530 m]. More than 4,100 ft [1250 m] of core was obtained from the three wells; more than 1,100 ft [335 m] of it is oriented.
Geologic and Sedimentologic Setting
The fluvial Sandstone E lens, the reservoir of interest for this study, is one of many Late Cretaceous, fluvial lenticular deposits of the Williams Fork formation of the Mesaverde group. The fluvial interval is found at depths of about 4,300 to 6,000 ft [1300 to 1800 m] in the MWX wells. The strata in this interval were deposited on a low-relief alluvial plain. Major reservoir sandstones within the fluvial interval are meanderbelts that are intimately interbedded with heterogeneous mudstones, sandstones, siltstones, and carbonaceous shales.
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