ABSTRACT:

The feasibility and design of microfracturing formation stress tests requires an initial assessment of the conditions expected to be met in situ (state of stress, rock tensile strength, etc.). When data are scarce and such assessment is difficult, insight can be gained by reviewing the results of previous tests completed—successfully or not—in similar conditions. We present a field case example of such inversion on a series of tests undertaken in a deepwater, Gulf of Mexico oilfield. In the present example, inversion results explain the average success rate of the series (2/7) and reduce the overall level of uncertainty by a factor of three, with most gain made on the minimum horizontal stress, horizontal stress anisotropy ratio, pore pressure, and rock tensile strength parameters. Inversion results also reveal the heterogeneity of the conditions experienced by the tests. We then show how such return of experience can be leveraged to improve the chance of success of future stress testing operations. We illustrate such planning with recommendations in terms of mud density, formation targets, and tool configuration. Finally, we take this opportunity to expand the risk analysis framework to deviated wells, including the risk of creating tortuous fractures.

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