Poroelastic contribution to the reservoir stress path |
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| Authors: | Johannes B Altmann Tobias M Müller Birgit IR Müller Mark RP Tingay Oliver Heidbach |
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| Affiliation: | 1. Geophysical Institute, University of Karlsruhe, Hertzstrasse 16, 76187 Karlsruhe, Germany;2. CSIRO CESRE, Australian Resources Research Centre, 26 Dick Perry Avenue, Kensington WA 6151, Australia;3. Australian School of Petroleum Science, University of Adelaide, Australia;4. Helmholtz-Zentrum Potsdam, Deutsches GeoForschungsZentrum GFZ, Potsdam, Germany;1. Department of Geoscience and Petroleum, Norwegian University of Science and Technology (NTNU), S. P. Andersens veg 15a, 7031 Trondheim, Norway;2. Institute of Environmental Assessment and Water Research (IDAEA), Spanish National Research Council (CSIC), Jordi Girona 18-26, 08034 Barcelona, Spain;3. Associated Unit: Hydrogeology Group (UPC-CSIC), Spain;1. Lawrence Berkeley National Laboratory, Earth Sciences Division, CA, USA;2. GeoAzur, University of Nice Sophia-Antipolis, Côte d’Azur Observatory, France;1. Swarbrick GeoPressure Consultancy, University of Durham, UK;2. Lahann Geoservices, Indiana Geological Survey, USA;1. Key Laboratory of Tectonics and Petroleum Resources (China University of Geosciences), Ministry of Education, Wuhan 430074, China;2. China National Offshore Oil Corporation, Beijing 100010, China;3. Zhanjiang Branch of China National Offshore Oil Corporation Ltd, Zhanjiang 524057, China |
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| Abstract: | Pore pressure/stress coupling is the change in the smaller horizontal stress σh associated with changes in pore pressure P, and has been measured in numerous reservoirs worldwide. These measurements suggest that the change in minimum horizontal stress Δσh is on average ca. 64% of the change in the reservoir pore pressure ΔP, but can be as low as 34% and as high as 118%. Conventionally it is assumed that the total vertical stress σv, given by the overburden, is not affected by changes in pore pressure, in contrast to the horizontal stresses σH and σh. We investigate analytically and numerically the spatio-temporal pore pressure and stress evolution in poroelastic media for continuous fluid injection at a point source, and calculate from the numerical modelling results the ratio Δσ/ΔP. Analytically, we show that the measured average of Δσh/ΔP can mathematically be deduced from the long-term limit of the spatio-temporal evolution of pore pressure and horizontal stress caused by fluid injection at a point source. We compare our numerical results to the analytical solution for continuous point injection into homogeneous poroelastic media as well as to Δσh/ΔP values measured in the field, and show that all stress components change with a variation in P. We use the concept of poroelasticity to explain the observed coupling between pore pressure and stress in reservoirs, and we consider different measurement locations and measurement times as one possible reason for the measured variation in Δσh/ΔP in different oil fields worldwide. |
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