A joint theoretical/experimental research program on hydraulic fracturing, is being conducted. Newly developed numerical models have been applied to analyze some aspects of fracture propagation near well-bonded material interfaces to determine whether these interfaces can inhibit propagation. Results from these calculations indicate that, for fractures propagating from a lower modulus material toward an interface with a higher modulus material, the stress-intensity factor at the tip near the interface decreases significantly as the tip approaches the interface. However, upon penetration of the interfaces into the higher modulus material, the stress-intensity factor increases abruptly and arrives at a higher value than in the lower modulus material. Conversely, when the fr cture is propagating from a higher modulus material toward a lower modulus material, the situation is reversed. The presence of fractures near the interface significantly reduces the effects of these phenomena. Dynamically, where wave-mechanics effects are taken into consideration, the change in material properties also affects fracture propagation across an interface.

Small-scale laboratory experiments are being performed to study the growth of hydraulically driven cracks in the vicinity of unbonded interfaces in rocks. Blocks of the materials being studied are held adjacent to one another under a static load, and a hydraulically driven crack is initiated in one of the blocks. For blocks of the same material, penetration of the crack into the adjacent block is controlled by the normal stress across the interface and the finish of the interface surfaces. Experiments have been performed to measure the frictional properties of the interfaces to understand better the mechanism of crack growth across the interface.

The LLL dry-hole sonic logging tool was applied in Columbia 20569 gas well, Mingo County, West Virginia. Although some problems were encountered in the application of the tool, data were collected and analyzed to locate reflection loci near the well bore at distances up to several meters.

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