In the tight Cotton Valley sands of Louisiana and Texas, seven wells stimulated with an average of 1,390,000 lbs of 20/40 sand provided identical initial rates (2.9 MMcfd) to three wells treated with an average of 179,000 lbs of HSP. However, after decline, the HSP wells outperformed the sand wells, producing an average of 1.1 MMcfd compared to 0.7 MMcfd for the sand wells. Despite pumping 8-times more sand, the HSP wells had less steep declines, suggesting the improved proppant permeability was more important than the reduced fracture dimensions
Numerous laboratory tests on Cotton Valley core samples have been conducted that compare Ottawa sand and sintered bauxite in terms of their ability to perform as a propping agent under varying closure perform as a propping agent under varying closure stresses. Computer simulation has also been used as an aid in selecting the optimum proppant type and pack configuration for a given fracture treatment. However, in spite of the information obtained from these sources, there remains some uncertainty as to the value of closure stress at which a high strength proppant should be incorporated into the fracture treatment design.
Data obtained from Cotton Valley wells indicates that the producing rate was significantly reduced beyond the normal decline when a certain closure stress was reached. An examination of offset wells that experienced a lesser closure stress or were fractured with bauxite reveals that this abnormal decline is not present. This comparison indicates the fracture conductivity, and consequently the producing rate were significantly altered as a result of sand crushing.
Author(s): Clark, H.C., Mitchell Energy Corp.
Paper Number: SPE 11617