Thermal Expansion Of Rocks Research Articles

Impact of fracture shear dilation on long-term heat extraction in Enhanced Geothermal Systems: Insights from a fully-coupled thermo-hydro-mechanical simulation

Shear dilation of fractures has been recognized as a main mechanism of permeability enhancement by hydraulic stimulation in Enhanced Geothermal Systems (EGSs); however, the interactive role of fracture shear dilation and thermo-hydro-mechanical (THM) coupling processes in long-term heat extraction performance of EGSs remains unclear. In this study, we develop a novel THM coupling model based on the discrete fracture network approach, which can realistically capture important processes including hybrid normal-shear deformation of fractures, thermal expansion of rocks, fluid flow in both fractures and rocks, and heat convection/conduction as well as local thermal non-equilibrium effect and changes in physical parameters of fluid. We quantitatively investigate the effects of fracture network geometries and geomechanical boundary constraints on fracture shear dilatancy, and the resulting heat transfer characteristics of EGSs. Numerical results reveal that shear dilation of fractures can be triggered by transient pore pressurization and thermal stress under anisotropic in-situ stress condition, and would severely engender flow channeling as well as anisotropic heat transfer, which strongly impact the heat extraction performance. The production temperature tends to be overestimated while the thermal production rate may be underestimated, if the shear dilatational behavior is not incorporated. Increased in-situ stress ratio and injection/production pressure would magnify the effects of shear dilation, and lead to considerable enhancement of fracture permeability, eventually resulting in much earlier and quicker temperature drop. Excessive increase of fracture density and the location of injection-production wells parallel to potential channelized flow paths, formed by intersected fractures preferentially oriented for shear sliding, tend to form short circulating flow paths and reduce the heat extraction performance. Our study demonstrates the importance of considering fracture shear dilation and fully-coupled THM behaviors when evaluating the long-term performance and efficiency of heat extraction in EGSs.

Experimental investigation of thermal expansion of organic-rich shales

Experimental data on thermal expansion of rocks are necessary for many applications involving wellbore stability analysis, designing radioactive waste repositories, etc. Such information is especially actual for organic-rich shales that exhibits significant thermal anisotropy and heterogeneity and were not studied comprehensively previously. The coefficient of linear thermal expansion (CLTE) of 23 shale samples from three wells of three oilfields of the Bazhenov and Abalak formations (West Siberia, Russia) was studied with a quartz dilatometer specially adapted for the measurements on standard core plugs. Differential CLTE of shales was determined within temperature range 25–300 °C through every 25 °C for directions parallel and perpendicular to rock bedding. Strong correlations between the CLTE, thermal conductivity, and total organic carbon were established. Detailed profiles of CLTE along studied wells were obtained due to application of the optical scanning technique. These profiles fit well with total organic carbon obtained with pyrolysis. CLTE anisotropy was assessed for organic-rich shale samples together with thermal conductivity anisotropy. The thermal conductivity measurements before and after heating allowed estimation of structural changes in rock samples during heating.

Anomalous surface heave induced by enhanced oil recovery in northern Alberta: InSAR observations and numerical modeling

AbstractRecent interferometric synthetic aperture radar observations over northern Alberta, Canada, show persistent surface heave occurring at rates of 1–4 cm/yr, localized at sites where the steam‐assisted gravity drainage technique is currently used to extract bitumen from the Athabasca oil sands. We find that uplift rates above the horizontal injector wells are strongly correlated with rates of steam injection, even though there is a net fluid loss from the reservoir pore space as oil and water are withdrawn through the production wells. In combination with available steam injection and bitumen production data at four sites, we use reservoir flow models to explain how the thermal and geomechanical effects of steam injection on an oil sand reservoir can generate uplift at the surface. Results of our numerical experiments show that persistent surface heave consistent with observed rates can be driven by stress changes in the reservoir due to porous flow and thermal expansion. We also observe an unexpected localized uplift, of magnitude equal to or greater than the heave above the sites of steaming but located at clusters of wellheads which are outside the region of influence of the steam chambers. We show that this “wellhead” deformation can be explained by thermal expansion of rock near the injector wells.

Effect of cracks on the thermal expansion of rocks : Cooper, H W; Simmons, G Earth Planet Sci Lett, V36, N3, Oct 1977, P404–412

Effect of cracks on the thermal expansion of rocks : Cooper, H W; Simmons, G Earth Planet Sci Lett, V36, N3, Oct 1977, P404–412

The effect of cracks on the thermal expansion of rocks

Thermal expansion during the first heating cycle at atmospheric pressure was measured in several directions in seven igneous rocks between 25° and 400°C at slow heating rates. The coefficient of thermal expansion measured under these conditions increases more rapidly as temperature is increased than the average thermal expansion coefficient of the constituent minerals. The “extra” expansion is attributed to the formation of cracks by differential expansion of mineral grains. The presence of such cracks in the rocks during the cooling part of the cycle and during any subsequent heating and cooling cycles will result in a substantial decrease in the coefficient of thermal expansion as compared to that measured during the first heating cycles. The effect of cracks initially present in a rock was studied by measuring the full tensor of the coefficient of thermal expansion on two rocks with anisotropic crack distributions. In these two rocks the coefficient of thermal expansion is least in the direction perpendicular to the plane of greatest crack concentration. The implication of our data is that thermal expansion depends greatly on the fracture state of the rock. Both the fractures in the rock and the boundary conditions on the rock are significant for the interpretation of thermal expansion measurements and for their application to other problems.

An apparatus for determining the coefficient of thermal expansion of rocks, mortars and concretes

Synopsis An apparatus for the determination of the coefficient of thermal expansion in the temperature range 20 to 80°C of rock, mortar and concrete specimens is described. The moisture content of the specimens can vary from oven-dried to saturation. Data showing the thermal expansion of rocks and mortars are presented.

Features of thermal expansion of rocks

Features of thermal expansion of rocks