Determination of in-situ stress from borehole deformation

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Knowledge of in-situ stress is critical to maximize the energy resource exploitation and to mitigate geologic and environmental disasters such as borehole collapse and gas leakage. Worldwide, subsurface energy resource industries are seeking effective and inexpensive means to quantify in-situ earth stress. Traditional approaches rely on information on borehole pressure, however, this method is prone to inaccuracies, because the complicated nature of the interaction between fluid transport and fracture dynamics causes uncertainty in the interpretation of the pressures that are used in in-situ stress inversion. Leak-off pressure data are scarce due to the nature of leak-off tests, and hydraulic fracturing tests incur high cost to obtain necessary borehole pressures. I have spent 10 years investigating an approach to use information on borehole deformation to estimate in-situ stress via soft-computing based inverse analysis, which is inexpensive and accurate, and has had initial success. However, there are still three challenges to investigate as objectives over the next five years: (1) the mechanisms for borehole deformation need to be differentiated and accounted for accordingly; (2) the high dimensionality of the optimization problem in the inverse analysis requires advanced soft-computing techniques; and (3) the non-repeatability of field-scale deformation of a borehole subjected to in-situ stress requires advanced numerical models for simulation. The objectives for the proposed program are: (1) To carry out laboratory true tri-axial tests focusing on study on the different mechanisms of borehole deformation. (2) To enhance the performance of high dimensionality of the optimization in inverse analysis for in-situ stress determination. (3) To develop advanced numerical models to simulate the borehole deformation based on mechanisms observed in laboratory. The proposed research program will provide an accurate and effective way of measuring in-situ stress magnitude, which has long been desired in subsurface energy resource industries. This program will boost the fundamental research on in-situ stress determination in rock mechanics and structural geology, while reducing the cost and enhancing the accuracy in the exploration stage of shale developments. In a broader view, not only will the oil/gas industry benefit from this program, but the mining, geologic CO2 storage, subsurface energy storage, and geothermal energy industries will also benefit from this program. All of these industries are concerned with caprock integrity, including the associated environmental and seismic concerns, and knowledge of in-situ stress is key to understanding caprock integrity. The proposed research program also provides unique training opportunities to for HQP to develop artificial intelligence based techniques that is highly desired by the subsurface energy industries.