New models for heater wells in subsurface simulations, with application to the in situ upgrading of oil shale

Abstract

Downhole electrical heating can be used to achieve the high temperatures required for in situ upgrading of oil shale or oil sands. Heater-well models are needed if this process is to be simulated accurately. The traditional Peaceman approach used for fluid injection and production wells may not be applicable because it does not capture transient effects, which can be important in downhole heater models. Standard models also neglect the effects of heterogeneity and temperature dependence in the rock properties. Here, we develop two new models for representing heater wells in reservoir simulators. The first model is applicable for homogeneous systems with properties that are not temperature dependent. For such cases, we develop a semi-analytical procedure based on Green's functions to construct time-dependent heater-well indexes and heater-block thermal transmissibilities. For the general case, which can include both fine-scale heterogeneity and nonlinearity due to the temperature dependence of rock properties, we present a numerical procedure for constructing the heater-well model. This technique is essentially a near-well upscaling method and requires a local fine-scale solution in the near-well region. The boundary conditions are determined using a localglobal treatment. The accuracy of the new heater-well models is demonstrated through comparison to reference solutions for example problems. The approach is then applied for the coarse-scale modeling of the in situ upgrading of oil shale, which entails a thermalcompositional simulation with chemical reactions. The model is shown to provide an accurate and efficient solution for this challenging problem.

An Efficient Multiscale Method for the Simulation of In-situ Conversion Processes

“…accumulated mass in each grid cell, mass flowing within each phase from neighboring grid cells, mass generated or removed through chemical reactions, and mass in-and outflow from wells. Thus, for flowing components i, one can express the mass-conservation equation as follows (adapted from Fan et al 2010):…”

“…In this work, we use a reaction model that is adapted from Fan et al (2010). The model has five components, which are labeled as kerogen, C 37 , C 13 , C 2 , and CO 2 .…”

“…Various thermal reservoirsimulation approaches were developed for ICP, and the results of a few studies were reported in the literature (Shen 2009;Fan et al 2010). These studies feature simulation models designed for pilot projects, which are typically small in size and therefore require only relatively small simulation models.…”

“…Shifting the focus of ICP modeling from pilot to a larger commercial-scale pattern will clearly require the application of approximating techniques that retain sufficient accuracy of the fine-scale solutions, but reduce simulation times. The upscaling method reported in Aouizerate et al (2012) can be seen as a step in this direction.…”

“…We do not aim to investigate or improve accuracy, recovery efficiency, or any other aspect of the ICP recovery process in this paper. Therefore, we resort to the basic ICP model of Fan et al (2010) to apply our novel multiscale technique. Even though this model lacks some important features of realistic ICP-water is absent, nor is coke formation included in the reaction scheme-the model captures enough of the essential characteristics of ICP to make it a valid test bed for our multiscale technique.…”