Because of the very large number of wells in a typical development, and because the wells require fracture stimulation, shale and tight sand unconventional projects may have large land, water, and air "footprints". Responding to rapid industry growth, the public has become concerned about the impacts of development on their communities. This has resulted in protests, moratoria, and bans against exploration in general and hydraulic fracture stimulation in particular. In order to gain social license to operate going forward, industry must be both responsible in fact and also seen to be responsible in mitigating these impacts and addressing concerns. Fortunately there are a number of technology opportunities that serve the twin goals of environmentally responsible operations and efficient exploration and development. For example in the exploratory stage, better models to predict the economically viable part of the play, and to know what to measure and how to assess productivity in early wells, will allow companies to drill fewer, widely spread single wells and more quickly move to multi-well pads in the ultimately developable area. Real-time monitoring of fracture stimulation gives feedback to optimize pumping strategies and increase per-well productivities. Shear stimulation can require less water than current practice, which helps both the source and disposal sides of the process. Fit-for-purpose drilling rigs of the future can be tuned to the minimum necessary size and require fewer staff to run. These examples and others are either already in hand or on the horizon, and are active areas of research for both service companies and many oil companies. They can be applied globally to lift the performance of all operators both in fact and also in public perception, thus helping to ensure continued access to these important resources for the future of our industry.
Thermal recovery processes can generate substantial porosity, permeability and mineralogical changes to carbonate rocks. Understanding these changes is critical to evaluate the success and safety of the process. Tests to evaluate these changes under steam soak conditions have been done on a carbonate bitumen reservoir rock. Thermal testing done in the presence of water at 265°C and 5.1 MPa (740 psi) under unstressed conditions for ~60 days showed considerable fracturing, dolomite dissolution, calcite precipitation, magnesium-clay formation, and carbon dioxide (CO2) generation above 240°C. Calcite precipitation in the matrix porosity and newly formed fractures was extensive. However, reservoir steaming conditions will be at lower temperature (180°C), pore pressure (1.0 MPa [145 psi], with primarily steam rather than water), and under confining stress (5.8 MPa [845 psi] horizontal, 6.7 MPa [970 psi] vertical). A 17-day steam-soak test in a triaxial pressure vessel under these reservoir conditions was done on an uncleaned core sample (~80% bitumen saturation) for comparison. Water/steam flowed through the sample at intervals indicated a relative permeability of 0.3 mD. At the end of the test the accessible (i.e., water filled) pore space was filled with epoxy under stressed conditions. The remaining bitumen was removed post-test before thin section manufacture. Thin sections from the post test sample were compared to thin sections made from untested end trims and adjacent core material, and to ones from the prior unconfined, higher temperature and fluid pressure testing. The sample tested under confined reservoir conditions also shows dolomite dissolution and neoformation of magnesium-clays. The amount of calcite precipitated is minor. However, calcium sulfate (CaSO4) (not observed in the pre-tested equivalent sample) appears as a by-product of the reaction. Newly formed open fractures are not observed in the test under lower temperature, lower pore pressure, confined conditions. This work highlights the importance of mimicking expected reservoir conditions (temperature, pressure, stress & steam) for evaluating thermal decomposition effects on reservoir rocks. Future tests will help to evaluate whether longer duration heating and flow at the lower expected temperature will produce similar reaction products and physical damage (including fracturing) as more bitumen is mobilized and larger surface areas are in contact with steam.
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