Geomechanical Reservoir State
- Measure deformation, porosity and permeability changes on oil shale samples subjected to representative in-situ stresses as well as engineered temperatures required for kerogen conversion and syngas production.
- Generate geomechanical, thermophysical and permeability data for use with complimentary ongoing research efforts (Reservoir Simulation of Reactive Transport Processes) and for validation efforts (In Situ Pore Physics)
- Topical Report assessing subsidence and compaction implications of in situ development of oil shale and oil sands.
Department of Energy, National Energy Technology Laboratory
Successful recovery of product from in situ oil shale and oil sands operations requires supplementing existing formation permeability by creating fracture networks and assuring that superjacent lithologies and the surface shall not subside substantially as a consequence of compaction of the pay zone. The fracture networks allow penetration of appropriate carrier media, removal of product, increased surface contact area, and reduced distance for movement of fluids from the matrix to a fracture system intimately connected to a production wellbore. These fracture systems can be newly created, reactivated, healed pre-existing discontinuities, etc. In oil sands, the fracture systems may be more channel-like, depending on the integrity of the native rock. Compaction could occur due to volumetric reduction accompanying kerogen conversion and syngas production. Alternatively, heave could occur during some stages of in-situ heating due to thermal expansion as well as supplementary fracture creation (dilation).
Research for this project shall include experiments to replicate in-situ production processes and determine the potential for creation of supplementary permeability and porosity; to evaluate potential methodologies for increasing contact area in the reservoir; and to determine thermophysical properties for complimentary simulations. A unique high pressure-high temperature vessel and an ancillary flow system has been designed (Figure 1) to carry out measurements representing oil shale response to high-temperature in situ processes under realistic pressure and stress conditions. Measurements will assess strength, fracturing potential, fracture and matrix porosity creation and yield, and temperature-dependent thermophysical properties required for various simulations. This task builds on legacy literature, including a paper by Budd et al. (1967) addressing strength parameters in relationship to anisotropic bedding structure and work by Petrofsky (1973) and Tisot (1967) on measurement of mechanical properties.
Examples of tests to be performed include (1) thermal loading measurements to duplicate generic in situ temperature profiles under static but representative in situ stress conditions and to assess the consequences of the stresses and temperatures on generation of fracture and matrix porosity and permeability, (2) temperature-dependent thermophysical properties required for simulations including thermal conductivity and diffusivity, (3) temperature-dependent thermomechanical properties required for simulations as a function of process history including the coefficient of thermal expansion.
Figure 1: (Left) Preliminary pressure vessel design. (Right) Elevation cross-section through the vessel, designed to accommodate 4-inch diameter oil shale sample and simulate processes with temperatures of 1000°F, 10,000 psi axial stress, and confining pressure of 1500 psi.
1 Budd, C.H., McLamore, R.T., and Gray, K.E. (1967). "Microscopic examination of mechanically deformed oil shale," SPE 1826, 42nd Annual Fall Meeting SPE, Houston, TX, October 1-4, 1967.
2 Pelofsky, A. H. (1973). "Composition And Reactions Of Oil Shale: A Review," SPE 4433.
3 Tisot, P. R. (1967). "Alterations in structure and physical properties of Green River oil shale by thermal treatment," J. Chem.