Production-time diagrams of fluids produced from three tight gas accumulations in Wyoming’s Madden field showed little or no correlation between gas and water, a new US Geological Survey study found.
The fluid production diagrams from the Cody Shale, Mesaverde Formation, and lower Fort Union Formation in the Wind River Basin had disparate gas and water signatures, according to the report which USGS posted at its website on July 1.
“Fractional change in gas and water production during a five-year period was greatest in the Cody Shale and least in the lower Fort Union Formation. Water production generally commenced with gas production and increased or decreased with time while gas production generally decreased,” it said.
The study by Philip H. Nelson, Patrick K. Trainor, and Thomas M. Finn determined that well position along the Madden anticline did not seem to control fluid production, and that the initial magnitude of gas production was not a determinant of either the magnitude or the sense of subsequent water production.
“We conclude that gas and water production from tight gas accumulations in the Madden field are generally independent of one another, and a speculative model linking tectonics, timing of gas generation, and fracture flow has been proposed,” it said.
The study also said that an examination of vector diagrams from three fields (Frenchie Draw, Cooper Reservoir, and Madden) in the Lower Fort Union Formation showed that the three accumulations responded differently over time.
In Frenchie Draw wells, gas declined slowly and at about the same rate as in Madden, but water did not change (with one exception), while water production either increased or decreased in Madden, it said. Both gas and water declined at much higher rates in the Cooper Reservoir field than in either Frenchie Draw or Madden, it indicated.
“The differences in water and production may indicate that fracturing plays a smaller role in Cooper Reservoir and Frenchie Draw than it does in Madden,” the study said.
The report, “Gas, Oil and Water Production in the Wind River Basin, Wyoming,” may be found online at http://pubs.usgs.gov/sir/2008/5225/.
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