A significant amount of research has been devoted in the past few years to the study of fracture containment in stimulation of low permeability gas reservoirs. One finding of this research is that vertical fracture growth is controlled by contrasts in the in situ stress state. A knowledge of the variation of horizontal stress with depth would aid in the design of well stimulation.

The only method available today for determining in situ stress at depths greater than about 200 meters is a small scale hydraulic fracturing technique; stress calculations are based upon several relatively simple measurements; however, at present the economics of sending the tool downhole on a tubing string are unfavorable. To overcome this problem the design of a self contained tool which operates on a standard seven conductor wireline cable has been undertaken by Terra Tek, Inc.; funding is being provided by the U. S. Department of Energy, Morgantown Energy Technology Center. A major goal of the design effort is to build the tool primarily with commercially available components. The basic tool consists of a downhole hydraulic power supply control unit, straddle packers and pressure transducer; it has been designed to function in cased or open holes. Additionally, the tool design incorporates a fracture detection device so that orientation can be determined.

In conjunction with the tool design a laboratory investigation utilizing 1 meter cubic samples is being pursued to study the mechanics of stress determination in cased boreholes. Since there is very little published literature on the determination of in situ stresses through perforated casing, it is hoped that the laboratory investigations will allow stress determinations in cased wells with the same degree of reliability that now exists for stress determinations in open holes.

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