Thermal Oil Recovery Processes Research Articles

Influence of reservoir rock composition on crude oil pyrolysis and combustion

The principal objective of this study was to investigate the influence of reservoir rock composition on the pyrolysis and combustion behavior of crude oils in porous media in relation to in situ combustion (ISC) as a thermal oil recovery process. Using sand pack of varying mineralogical composition and different crude oils, pyrolysis and combustion tests were performed to examine how the clays affect the amount of fuel and its reactivity during the ISC process. From the experimental results, it appears that clay minerals present in the matrix enhance fuel deposition during the pyrolysis process and also catalyze the oxidation of fuel.

Elliptical Flow In Composite Reservoirs

Abstract Composite reservoir systems are frequently encountered in production or injection operations. In most of the recent modelling efforts a set of concentric cylinders has been used to describe a composite nature of a reservoir. Some systems, however, exhibit nonisotropical rock heterogeneities. In this paper, an elliptical flow model accounting for the non isotropic reservoir properties is proposed. The model describes the effects of the wellbore storage the wellbore skin and the front skin. The model sensitivity to the storativity, F, [defined by equation (AJ)] and mobility ratios and the front skin was investigated as well as the effect of these parameter on the flow characteristics Introduction Oil and gas reservoirs are frequently featured by heterogeneous rock and fluid properties. Formation heterogeneities may either be of a natural origin, such as vugs, or man-made; for instance, fractures intercepting wells, injected water bubbles, the burned or steam swept regions in thermal oil recovery processes, etc. Formations which are featured by radial or quasi-radial discontinuities in terms of fluid mobilities and hydraulic diffusivities are referred to as composite systems. The majority of studies on composite reservoirs provide the system description in terms of the radial coordinates; rock isotropy is [hen a necessary requirement. However, several situations exist when elliptical flow may occur: a case of anisotropic systems; a fracture intercepting a well water influx from an aquifer into an elliptical reservoir and the gravity override and/or underride in case of thermal processes. In the recent past, various aspects of elliptical flow under the reservoir conditions were investigated by Kucuk and Brigham(l), Obut and Enekin(2) and Stanislav et al.(3). The objective of this study is to determine the system sensitivity to a variety of parameters under the line source inner boundary condition. Mathematical Model A two-zone elliptical composite system is considered. Each region is featured by different fluid and rock properties. A well is located at the origin of the coordinate system as shown in Figure I. The model is developed subject to the following assumptions: single phase fluid of constant compressibility is considered; the Formation is characterized by a constant thickness and homogeneous properties in each of the two regions; the two-dimensional elliptical flow takes place in both regions; the front (the interphase between the two regions) is stationary during the test period. Other features of the model will be introduced in connection with the formulation of the boundary conditions. The dimensionless form of the flow equation can be written as follows: region I: Equation (1) (Available in full paper) Equation (2) (Available in full paper) Equation (3) (Available in full paper) Equation (4) (Available in full paper) Equation (5) (Available in full paper) Equation (6) (Available in full paper) Equation (7) (Available in full paper) Equation (8) (Available in full paper) The set of equations, equations (I) to (8), represents a complete mathematical description of the problem considered. All dimensionless quantities are defined in Appendix A. FIGURE 1. Coordinate system FIGURE 2, Effects of CO and Sh on P∞D for a homogenous system.

A TG/DTG kinetic model and its application in an in-situ combustion reservoir simulator

In-situ combustion is a thermal oil recovery process in which crude oil undergoes a large number of physical and chemical transitions. The chemical reactions involved are to a great extent responsible for the heat generation needed to sustain the combustion front. The kinetic model used to predict the performance of the process needs therefore to be as accurate as possible. To date, all kinetic models used in in-situ combustion simulators have assumed Arrhenius-type reaction rate constants and constant activation energies and heats of reaction. In this study the TG/DTG curve of the crude oil under study is used to derive a kinetic model suitable for the simulator. The model does not include the assumption that the specific reaction rate constants be of Arrhenius type and thus does not require explicit values of activation energies and frequency factors. An in-situ combustion tube test was simulated using the present kinetic model and compared with the simulated results obtained by incorporating a commonly used kinetic model. Process variables predicted from the present model were significantly closer to the actual experimental values than those predicted by the old approach. More importantly, to arrive at a reasonable predicted performance for the process using the old technique, the values of activation energies in the kinetic model had to be lowered to unrealistic levels.

The Production Of Conventional Heavy Oil Reservoirs With Bottom Water Using Steam-Assisted Gravity Drainage

Abstract Developing and producing conventional oil economically from reservoirs containing bottom water is' one of the most challenging technical problems in Canadian petroleum engineering This paper investigates a new, innovative thermal oil recovery process that shows potential for the economic of production heavy oil from reservoir when recovery is limited by water coning. The process as envisaged at present, would use parallel horizontal wells placed near the bottom of the reservoir with horizontal steam injection wells located vertically above the producers near to the top of the reservoir. Experiments were performed using a scaled, two-dimensional reservoir model containing an active aquifer system. The model was designed to provide dimensional similarity with specific "Lloydminister-type heavy oil" field conditions. The study investigated the mechanism, the process and the effects of steam injection Pressure, bottom water thickness, and the location of the production well; the laboratory results were extrapolated to the field conditions. It is shown that the process may produce heavy oils economically. The severity of steam coning is because the high productivity index of a horizontal well, allows practical production alrates which are below the critical steam coning rates. Water production from the aquifer is greatly reduced by operating the production wells at pressures close to that of the aquifer. The cumulative oil recovery varied from 48% (bottom water case with 41% water in the model) to 87% (no bottom water with 0% water in the model) of original oil-m-place above the production well (OOIP*). The thickness of the bottom water zone and The well configurations employed had a significant effect on the cumulative oil recovery. Introduction In Canada, there i, a vast amount of heavy oil reserves (3.5 million M3) underlying the Lloydminster area of Alberta and Saskatchewan(1). These heavy oils are usually mobile al reservoir conditions and most can be produced at a low ultimate recovery by primary production. Waterflooding is not effective because the mobility ratio of heavy oil to Water is not favourable. Most heavy oil reservoirs in Saskatchewan have thin pay zone, which have been judged unsuitable for thermal recovery. Many of the thicker reservoirs have underlying water, Attempts to produce such reservoirs by conventional means result, quickly, in the production of excessive water. The mechanism for this is well understood and is a result of the much lower viscosity or water compared to that of the oil; the Water "cones" upward into tlte well. The conventional steamflood or in situ combustion processes are usually unsuccessful due to prohibitive heat loss or air channelling through the underlying water and also excessive water will be produced(2). Therefore, the chance of recovering this type of petroleum reserves is further limited. An advantage of the technique Studied here is that the process can be operable, even though there is a significant underlying water layer. The reason that the water can be tolerated is that the pressures involved in the SAGD process, can be adjusted so that there is no tendency for water to now from the aquifer to the production well(s).

A block preconditioned conjugate gradient-type iterative solver for linear systems in thermal reservoir simulation

A preconditioned residual-norm-reducing iterative solver is described. Based on a truncated form of the generalized-conjugate-gradient method for nonsymmetric systems of linear equations, the iterative scheme is very effective for linear systems generated in reservoir simulation of thermal oil recovery processes. As a consequence of employing an adaptive implicit finite-difference scheme to solve the model equations, the number of variables per cell-block varies dynamically over the grid. The data structure allows for 5- and 9-point operators in the areal model, 5-point in the cross-sectional model, and 7- and 11-point operators in the three-dimensional model. Block-diagonal-scaling of the linear system, done prior to iteration, is found to have a significant effect on the rate of convergence. Block-incomplete-LU-decomposition (BILU) and block-symmetric-Gauss-Seidel (BSGS) methods, which result in no fill-in, are used as preconditioning procedures. A full factorization is done on the well terms, and the cells are ordered in a manner which minimizes the fill-in in the well-column due to this factorization. The convergence criterion for the linear (inner) iteration is linked to that of the nonlinear (Newton) iteration, thereby enhancing the efficiency of the computation. The algorithm, with both BILU and BSGS preconditioners, is evaluated in the context of a variety of thermal simulation problems. The solver is robust and can be used with little or no user intervention.

Effect of lateral heat losses on the stability of thermal displacement fronts in porous media

AbstractPrevious studies have shown that heat transport by horizontal conduction in thermal displacement processes in porous media has a stabilizing effect on condensation fronts. This paper expands the stability analysis by also including the description of heat transfer lateral heat losses by conjungate (vertical) conduction. A marginal stability condition is derived in terms of a parameter Λ representing the relative magnitude of heat transfer by conjugate conduction. It is shown that lateral heat losses ask a significant stabilizing effect on the front. This effect should be important in thermal oil recovery processes such as steam injection and in‐situ combustion.

Heat transfer ahead of moving condensation fronts in thermal oil recovery processes

This is a study of heat transfer in the liquid zone preceding an advancing condensation front in a 1-dim oil reservoir undergoing a thermal recovery process such as hot waterflood, steam injection or in situ combustion. A model is developed that allows for heat transfer by horizontal conduction and convection in the reservoir and by vertical (conjugate) conduction in the surrounding the reservoir formations to account for the lateral heat losses. The model is formulated in terms of an integro-differential equation involving an integral representation of the lateral heat losses for a region with a moving boundary. According to the magnitude of the Peclet number, and the velocity of the advancing front, various analytical expressions that describe the temperature distribution in the hot liquid zone are derived. The discussion emphasizes the cases Pe ⪢ 1 (high injection rates) and Pe = 1 (low injection rates). The case of arbitrary Pe is treated by a quasisteady state approximation

Some Thermal Characteristics of Porous Rocks

Published in Petroleum Transactions, AIME, Volume 213, 1958, pages 375–378. Abstract Results of experimental measurements of heat capacities and thermal conductivities of some typical porous rocks are presented. Measured heat capacities agree closely with values calculated from known chemical compositions of the rocks. On the basis of this agreement, heat capacities of fluid-saturated rocks were calculated. Thermal conductivities of the rock samples were measured under various conditions of fluid saturation. From these data thermal diffusivities were calculated. A significant variation of thermal diffusivity with temperature is indicated. Introduction Knowledge of the thermal characteristics of fluid-bearing porous rocks has become increasingly important with the development of thermal oil-recovery processes. Reliable thermal data for petroleum reservoir rocks are not available and approximate values are generally assumed for reservoir calculations. The effects of temperature, pressure and fluid saturation on thermal properties of porous rocks have not been carefully studied. The purpose of the present work was to measure and report the thermal characteristics of some typical porous rocks. A group of eight sedimentary rock samples, including limestone, shale, sandstone and siltstone, was selected for the study. Properties reported include heat capacities, thermal conductivities and thermal diffusivities. The effect of fluid saturation on these properties was also considered. Determinations of thermal properties require precise measurements which are time consuming and difficult to reduce to a routine basis. Methods have not been developed for measurement of thermal properties under conditions of pressure, temperature, and fluid saturation, which may be encountered in thermal recovery processes. As one approach to these problems, some preliminary work on methods of estimating thermal properties from other more readily measurable characteristics of the rock-fluid system is reported.

An Analog Computer for Studying Heat Transfer During a Thermal Recovery Process

Published in Petroleum Transactions, AIME, Volume 204, 1955, pages 205–212. Abstract A design is presented for an electrical analog computer which can solve non-steady state heat transfer problems in an extensive radial formation containing a moving cylindrical source. The computer is used to simulate a simplified thermal oil recovery process in which heat transfer from a moving, constant temperature source takes place radially by conduction only. Temperature distribution curves are shown for several different assumed modes of travel for the heat source. The data are used to estimate the residual fuel requirements necessary to maintain a self-propagating isothermal front for the particular system being studied. Although the computer is designed to represent an unique system, conversion factors can be adjusted to show the effects of changing the assumed values of system constants, such as thermal conductivity of the formation and temperature of the source isotherm. Examples are given to illustrate the relative influence the assumed values of these variables will have upon the quantity of fuel required to maintain the source. The maximum effect of heat transfer by the flowing air stream is estimated mathematically, and full requirements for this system are shown to be markedly reduced. Inasmuch as the examples discussed refer to a simplified process, the results are not directly applicable to a practical field operation. It is believed, however, that the data illustrate some general trends which are important in thermal recovery processes. Data from laboratory and field experimentation can be used to modify the computer to take into account the influence of heat transfer by various mechanisms, for example, by injected air and by fluids ahead of the hot zone. With such refinements it would be possible to estimate more accurately the limiting values for the rate of travel of the high temperature front and for the required air injection rates. Use of this computer should aid in evaluating the economic feasibility of oil recovery by various thermal processes. It is hoped this paper will stimulate further work by others to help accomplish this objective.