Feasibility and Design of Hydraulic Fracturing Stress Tests Using a Quantitative Risk Assessment and Control Approach

Openhole microfracturing stress tests often fail at great depth because a fracture cannot be initiated, even with application of the equipment's maximum pressure. This paper presents methodological developments enabling feasibility assessment and design analysis of such tests with respect to fracture initiation. Emphasis is put on quantitative risk assessment and control to account for the large uncertainty that generally prevails, before a test, in the in-situ conditions controlling the initiation pressure. Given equipment's pressure specifications, we calculate the probability of successfully initiating a fracture for a range of in-situ conditions and design options. Global sensitivity analyses are carried out to map the chance of success over this range. Finally, on test completion, we use test results to reduce the uncertainty space. We illustrate the method with a synthetic case example. Uncertainties prove easily factored in and run-time is less than one second for adequate sampling of the uncertainty space. The analysis informs on how successful or unsuccessful a planned test is likely to be and, when necessary, on the most effective ways to improve the chance of success, including in terms of tool configuration, well and test design, and rock formation targets. Uncertainty reduction based on completed tests results should improve the success rate from one test, or one test campaign, to the next.