An Experimental Study of Pressuremeter Testing Under Polyaxial Boundary Stress Condition
The in-situ stress is a critical factor that needs to be assessed in the development of a safe and sustainable oil and gas recovery, but it is also difficult to be accurately measured with the existing methods, especially in the soft sedimentary formation
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Department of Civil and Environmental Engineering, University of Alberta, Edmonton, Canada [email protected] Research Institute of Petroleum Exploration and Development of PetroChina, Langfang, China
Abstract. The in-situ stress is a critical factor that needs to be assessed in the development of a safe and sustainable oil and gas recovery, but it is also difficult to be accurately measured with the existing methods, especially in the soft sedimentary formations. In this paper, pressuremeter testing, as one of the promising approaches for the in-situ stress determination, is evaluated under a well-controlled polyaxial boundary stress condition. The experiment setup and test procedure are described. The data for the tests under three different stress regimes are presented. The data is corrected for the eccentricity and the movement of the tool during the test to show the non-uniform deformation of borehole in the testing plane. The discrepancy of pressure-expansion curves obtained at different axes is in a good agreement with the theoretical findings showing the effect of the in-situ stress anisotropy on the cavity expansion. Keywords: Pressuremeter testing
Stress anisotropy
1 Introduction One of the challenges in the development of the underground resource extraction plan is the uncertainty of in-situ stresses. In the oil and gas industry, an inaccurate estimation of the in-situ stresses would not only lead to the unfavorable design of well completion and but also put the disastrous events, such as the fault activation and the surface subsidence, under poor control (Zoback 2010). In Alberta, the in-situ stress plays a critical role in the assessment of the caprock integrity in the steam stimulation projects, as the minimum in-situ horizontal stress in the caprock is a primary factor to constrain the pressure of the steam injected into the oil sands reservoir. Methods, such as hydraulic fracturing and overcoring, have been developed and proved successful in determining the stresses in hard rocks (Ljunggren et al. 2003; Schmitt et al. 2012). However, because caprock formations are more ductile and less prone to fracturing, the validity of applying these methods to such the materials should be questioned (ShafieZadeh and Chalaturnyk 2014). © Springer Nature Singapore Pte Ltd. 2018 L. Hu et al. (Eds.): GSIC 2018, Proceedings of GeoShanghai 2018 International Conference: Multi-physics Processes in Soil Mechanics and Advances in Geotechnical Testing, pp. 449–457, 2018. https://doi.org/10.1007/978-981-13-0095-0_50
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L. Liu et al.
Pressuremeter testing, as one of the commonly used methods in the geotechnical investigation, is considered as a promising method in the evaluation of in-situ stresses in the soft rocks. The response of the borehole at the different orientations under the uniform expansion pressure could provide valuable information to back calculate the possible anisotropy of in-situ stresses in the testing plane. Figure 1 shows the one dataset obtained from the pressuremeter test in a horizontal boreh
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