This paper reports the results of field measurements carried out in four horizontal wells all of which were fractured in the course of this investigation, with a total of 68 fractures. The engineering basis for these measurements was detection of fracture shadowing (created by a combination of stress and pressure shadowing) created by the extending fractures. The results are used to develop a field-based engineering foundation for determination of fracture orientation and extent, spacing between wells, and the optimum number and spacing between fracture stages. Two of the four wells served as observation wells throughout the project while the other two were actively being fractured. Pressure gages were installed in each of the two observation wells.

Our findings show that we were able to detect fracture shadows generated by every stage of active fracturing. All the created fractures had a consistent northeast-southwest orientation, many were asymmetrical with respect to the wellbore, their propagation pattern was off-balance, and none of them intersected any of the many other existing fractures within the experiment domain. Some of the fractures had intersected and extended beyond the adjacent cased horizontal holes. The results also provided working approximations of the created fracture lengths.

A fortuitous coincidence of events allowed us to detect fractures created during the measurement period from another nearby well more than 1000 ft away. The fact that through fracture shadowing we were able to detect fractures so far away is quite remarkable. Furthermore, the general fracture growth pattern was consistent with the findings from the other four wells. The major advantage of the proposed approach is simplicity of operations, ease of analysis, and the high quality of results.

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