Conventional Thermal Simulation Research Articles

Models of Thermal Enhanced Oil Recovery in Fractured Reservoirs

Summary Models for steam or hot-water injection into a fractured diatomite or shale reservoir are developed from existing analytic models of energy transport and countercurrent imbibition. Radial convective heat flow through a horizontal fracture system is modeled with conductive heat flow into the low-permeability matrix. The flow geometry approximates hot-fluid injection into a five-spot pattern. Recovery mechanisms accounted for in the models include capillary imbibition and thermal expansion. Temperature dependence of viscosity and interfacial tension (IFT) are included in the imbibition estimate. Laboratory data are needed to quantify the magnitude of the imbibition mechanism, which is usually the primary contributor to oil recovery. Reservoir properties representative of either the Belridge Diatomite or the Antelope Shale, two giant fractured oil reservoirs, are used for the model forecasts. Currently, however, only temperature-dependent imbibition data for diatomite reservoirs are available. The steamflood model has been partially validated against a large-scale project in the Belridge Diatomite. By use of public-domain information, a reasonable comparison was obtained between the model and the field project during a 4-year injection period. Comparison with conventional thermal simulation was also performed, and it indicated reasonable agreement with the steamflood analytical model. The models have been used to determine the key factors determining the success of thermal recovery in fractured, low-permeability reservoirs. Steam injection is shown to be superior to hot-water injection in heating the matrix. Key factors enhancing recovery include reduced fracture spacing, increased matrix permeability, and increased injection temperature. Model results indicate that steamflood recoveries of more than 40% of the original oil in place (OOIP) may be achieved by injection in diatomite containing light oil. Application to diatomites containing heavy oil also shows good performance. Successful application in diatomite reservoirs is forecast to be possible in the current low oil-price environment. Economic application in fractured shales, assuming similar imbibition behavior as in diatomites, would require a higher oil price because of the higher well costs and lower oil content relative to diatomite projects. Because of the significant volumes of remaining oil in place (OIP) in both the diatomite and shale reservoirs, the application of thermal enhanced oil recovery (EOR) to these resources represents the logical next step in steamflood development.

Characterizing processor thermal behavior

Temperature is a dominant factor in the performance, reliability, and leakage power consumption of modern processors. As a result, increasing numbers of researchers evaluate thermal characteristics in their proposals. In this paper, we measure a real processor focusing on its thermal characterization executing diverse workloads. Our results show that in real designs, thermal transients operate at larger scales than their performance and power counterparts. Conventional thermal simulation methodologies based on profile-based simulation or statistical sampling, such as Simpoint, tend to explore very limited execution spans. Short simulation times can lead to reduced matchings between performance and thermal phases. To illustrate these issues we characterize and classify from a thermal standpoint SPEC00 and SPEC06 applications, which are traditionally used in the evaluation of architectural proposals. This paper concludes with a list of recommendations regarding thermal modeling considerations based on our experimental insights.

Characterizing processor thermal behavior

Temperature is a dominant factor in the performance, reliability, and leakage power consumption of modern processors. As a result, increasing numbers of researchers evaluate thermal characteristics in their proposals. In this paper, we measure a real processor focusing on its thermal characterization executing diverse workloads. Our results show that in real designs, thermal transients operate at larger scales than their performance and power counterparts. Conventional thermal simulation methodologies based on profile-based simulation or statistical sampling, such as Simpoint, tend to explore very limited execution spans. Short simulation times can lead to reduced matchings between performance and thermal phases. To illustrate these issues we characterize and classify from a thermal standpoint SPEC00 and SPEC06 applications, which are traditionally used in the evaluation of architectural proposals. This paper concludes with a list of recommendations regarding thermal modeling considerations based on our experimental insights.

Iterative Coupling Between Geomechanical Deformation and Reservoir Flow

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 97879, "An Overview of Iterative Coupling Between Geomechanical Deformation and Reservoir Flow," by D. Tran, SPE, L. Nghiem, SPE, and L. Buchanan, SPE, Computer Modelling Group Ltd., prepared for the 2005 SPE International Thermal Operations and Heavy Oil Symposium, Calgary, 1–3 November. With the help of geomechanics, many physical phenomena can be explained (e.g., reservoir compaction and subsidence, casing failure, or pore collapse). Several methods for coupling geomechanics to fluid flow in the reservoir have been proposed. The iterative-coupled method has proved effective. Introduction The coupling of a reservoir simulator to a geomechanics module has wide application in petroleum production. With the aid of geomechanics, many phenomena can be explained, such as compaction, subsidence, wellbore stability, and pore collapse, as well as loss and gain in production. In a traditional reservoir simulator, subsidence can be estimated by a simple formula without knowing the geomechanical response. In some problems, such as primary production and linear materials, the subsidence computed by a reservoir simulator alone may give results that are comparable to the coupled solutions. Yet, when nonlinear materials are used, the results obtained with a conventional simulator will be much different from those obtained with a flow/geomechanics-coupled simulator. The main reason is that in a coupled simulator, the flow is affected strongly by the stress and strain through the porosity. However, in a conventional simulator, this stress dependence is ignored. Therefore, if a stress-sensitive reservoir is considered, the solution obtained from a conventional simulator cannot deliver expected results. In addition, for thermal problems, a conventional thermal simulator does not properly account for thermal stresses, the effects of which can be significant. The coupling between reservoir flow and geomechanical deformation can appear in various forms.The fully coupled approach is the tightest coupling because deformation and reservoir pressure and temperature are solved simultaneously.The iterative-coupled approach is less tight than the full-coupling method because the geomechanics calculations are performed one step after the reservoir-flow calculations.The explicit-coupled approach is considered a special case of the iterative-coupled approach. The information from a reservoir simulator is sent to a geomechanics module, but the calculations in the geomechanics module are not fed back to the reservoir simulator. Reservoir flow is not affected by the geomechanical responses calculated by the geomechanics module. The full-length paper details basic equations for reservoir flow and solid deformation to show how variables in those equations are coupled. Only the iterative-coupled approach and explicit-coupled approach are discussed. Examples related to different constitutive models such as an elastoplastic model, a plastic-cap model, and a pseudodilation/recompaction model are used to demonstrate the effects of such coupling.

Experimental and Simulation Study of High-Temperature Foam Displacement in Porous Media

SummaryHigh-temperature surfactant foams are simulated by modifying gas-phase mobility in a conventional thermal simulator. Both surfactant-alternating-gas (SAG) and gas/liquid-coinjection processes are modeled. Foam generation by leave-behind and snap-off as well as foam coalescence and trapping mechanisms are incorporated in the model by an equation for the number density of foam bubbles; gas-phase relative permeability and apparent viscosity are modified according to the bubble density. Pressure and saturation data of laboratory corefloods are successfully history matched with simulation results. Field-scale sensitivity studies of the steam-foam-drive process demonstrate how the coalescence rate affects the extent of steam diversion.