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Abstract The first full scale steam drive in Mount Poso Field began in 1971. Additional steam drive projects were begun in 1974, 1976, and 1977. All of the Upper Vedder reservoir in the main part of the Mount Poso Field is under steam drive. Oil production from the field is currently 13,000 barrels per day. This compares to extrapolated primary decline of 1700 barrels per day. per day. A thermal reservoir simulator has been used to determine the effects of various operating policies. Eliminating steam entry into the policies. Eliminating steam entry into the producers is the most significant process improvement producers is the most significant process improvement found. The mid field producers are the wells which recover most of the oil. The effect of losing one of these wells is shown. A thermal simulator has also been used to optimize the design of a steam drive in the largest remaining portion of the field. Pumping policy and the quality of injected steam have been investigated. The thermal simulator has helped us lay out an integrated engineering plan for the steam drives in Mount Poso Field. Introduction The Mount Poso Field is located approximately 14 miles north of Bakersfield, California. The field is six miles long and up to one mile wide. There are three main pay zones, the Upper Vedder, Lower Vedder and the Third Vedder. The reservoir dips 6 degrees to the west and is closed on the east by the Mount Poso Fault. There is a strong waterdrive in each of the zones. Figure 1 is a structure map of the Upper Vedder zone. The east-west extent of the Lower Vedder oil bearing sands is about half that of the Upper Vedder. The east-west extent of the Third Vedder oil bearing sands is about a quarter of the Upper Vedder. There is sand-to-sand contact across the faults in the downdip, central part of the field. Pressure data indicate these faults are partial barriers to fluid movement. The pattern for steam injection was determined from physical model studies. It consists of a row of steam injectors downdip just above the original oil-water contact and a row of steam injectors updip. The process is steam drive from the updip injectors. Steam is injected into the downdip wells for two to four years to heat the downdip area. This heating is designed to prevent the formation of a cold oil bank. Stokes et. al. described the operation of the steam drive projects in the Mount Poso Field. Stegemeier et. al. described vacuum models and their application to Mount Poso conditions. This paper presents the use of numerical reservoir simulators presents the use of numerical reservoir simulators to determine optimum operating policies for the Mount Poso Field. PRIMARY DEPLETION HISTORY MATCH PRIMARY DEPLETION HISTORY MATCH Previous engineering work on Mount Poso was primarily concerned with project feasibility and basic process design. A simplified picture of conditions at the beginning of steam injection was adequate for these purposes. Since the current study addresses problems of a more specific nature, a more detailed description of reservoir conditions at the start of steam drive was required. The most important simplifications used in the previous studies were those of a uniform initial oil saturation and a constant pressure or constant water influx rate at the downdip boundary of the prototype. These simplifications have important effects on process optimization. process optimization. In order to obtain a more detailed description of initial conditions at the start of steam injection, it was decided to history match the field average primary depletion of the Upper Vedder, Lower Vedder, and Third Zone for a prototype strip along dip using an isothermal implicit reservoir simulator. The basic reservoir and fluid properties of this prototype are listed in Tables 1 properties of this prototype are listed in Tables 1 through 5. The capillary pressure curves shown in Figure 2 were used. These curves were obtained from laboratory analyses of core samples.
Abstract A steam injection reservoir simulator was developed with the objective of improving the resolution of the information concerning the flow around a well and between wells. To accomplish this objective, it was necessary to develop the contiguous hyperhybrid grid refinement method. With better well region representation, it has been shown that hyperhybrid grid refinement is useful in studying well operating changes and well interactions, particularly when the regions are made contiguous. Local well effects, interwell interference, multiwell cyclic steaming and conversion to steamflood were examined using hyperhybrid grid refinement. The results of these studies are presented in a separate paper. It is recommended that contiguous hyperhybrid grid refinement be used for analyzing problems where the local well region behavior is important in the context of a field simulation. Furthermore, it is recommended that this refinement technique be used to study interwell interactions where near-well effects are important and the communication path between the wells requires better representation. Introduction At the present time, there are steam injection simulators that may be satisfactory if there are no sharp fronts for steamflood simulation. When it comes to cyclic steaming, simulators are suited best for single well modeling, but multiwell modeling is possible only with difficulties arising from the necessary adjustments of relative permeability, hysteresis, formation compressibility and grid size. Some adjustments may also be required for single wells; however, a radial grid system is better suited for representing a well. Effective fieldwide cyclic steam stimulation simulation is still in the future, when the next generation computers become available. It is recognized in the industry that computational hardware/software allow for the inclusion of a limited number of wells in a thermal simulator. Recent work illustrates this point well-their study contained 4,500 rectangular grids blocks and up to only eight wells. Even at present, a fieldwide cyclic steam stimulation simulation requires a tremendous amount of computer storage and computation time. Yet, such a simulation customarily employs a rectilinear grid that is inadequate for simulating radial flow-an essential flow feature of cyclic steam stimulation-near the wells. In recognition of the fact that the next generation computers are nearby, the objective of this work is to develop a tool that will provide an effective fieldwide simulation. The existence of the next generation computers will not eliminate the need to have radial geometry around the wells. MODEL DESCRIPTION This is the first model to use hyperhybrid grids in thermal simulation. A hybrid grid is defined as a cylindrical grid system embedded into a single fundamental rectilinear grid block and a hyperhybrid โ grid is defined as a cylindrical grid system embedded into several contiguous fundamental rectilinear grid blocks. These grids are illustrated in Figure 1. Regions 1, 3 and 5 are hybrid while Regions 2, 4 and 6 are hyperhybrid grids. In addition, this is the first model, black oil or thermal, to offer hybrid and hyperhybrid grid regions that can be contiguous.
Abstract Steam injection into fractured vugular formations is of great importance in Alberta, as well as in several countries in the Middle East. In Alberta alone, over one trillion barrels of oil occur in the Grosmont formation, where oil recovery would be possible only through steam injection into vugs and cavities. In spite of the importance of this problem, a solution is still lacking, and the few proposed approaches lack consistency or are based on conflicting assumptions. The present paper mathematically examines the governing equations in conduction healing - in particular, two of the more controversial premises, viz. the importance of the unsteady-state term and the assumption of a moving vs. a stationary boundary for a single block in the steam zone. This is accomplished analytically, first by means of a magnitude analysis, and next through a solution of the partial differential equations involved. It was found that any analysis of the fracture heating problem must retain the unsteady-stale term, and that the use of the moving boundary is superfluous in low mobility systems. It is shown that the convective term is two orders of magnitude smaller than the diffusive term. Findings of this study can be used in the area of modelling steam injection in heavy oil fractured reservoirs, .e. heat consumption by matrix blocks in the steam zone can be modeled using analytical solutions of heat conduction For physical properties other than those considered in this paper, evaluation of the Peclet No. indicates the order of error that will be introduced if convection is neglected. Introduction Heavy oil occurring in carbonate reservoirs, mostly fractured, is an important resource, which accounts for one third of total heavy oil world-wide. In Alberta alone, over one trillion barrels of bitumen occur in the carbonate Grosmont formation, where the existence of fractures enables injection into the reservoir. Processes like steam injection, or other thermal recovery methods, which have been used extensively to recover heavy oil from nonfractured reservoirs, were not applied to fractured reservoirs until the last decade or so. This was based on the belief that the injected fluid would bypass the oil through fractures, and not recover most of the oil, and that carbonate rocks are highly reactive at high temperatures. At the same time, the results of experimental, theoretical and pilot tests, whichhave been appeared in the literature since early 80's, show the feasibility of heavy oil recovery from fractured reservoirs using steam injection. The process is complicated by nature. Interaction of heat transfer mechanisms-conduction and convection-with fluid flow in two different media is the reason for the complexity of the process. Multiphase fluid flow occurs under interaction of gravity, capillary. diffusive and viscous forces, with different degrees of importance in fracture network and in primary porosity. For example, recovery is enhanced from matrix block when capillary forces are stronger and imbibition is active, and the reverse is true when gravity drainage is active. In the fracture medium the role of capillary force is traditionally neglected. However, many studies show a large effect of fracture capillary on the behavior of double porosity systems.
Steam-strip drive for recovering waterflood residual oil in watered-out reservoirs gives good to excellent sweep efficiencies. The stripping process is very effective in decreasing the waterflood residual oil to process is very effective in decreasing the waterflood residual oil to values well below the "distillation" residual value. Introduction In their pioneering paper on the steam-injection process, Willman et al. mentioned steam stripping, as an effective mechanism for reducing the microscopic waterflood residual oil saturation. Steam strips the residual oil and transports the oil vapors to the colder part of the reservoir. where they condense and are banked up in a movable oil bank. Since the lighter and more volatile components are preferentially stripped, the oil bank will be enriched with preferentially stripped, the oil bank will be enriched with lighter components. This also means that the residual oil directly behind the steam front will become more volatile as the process proceeds, because it has the same composition as the oil in the oil bank just ahead of the steam front. Consequently, the stripping process is becoming increasingly effective. In their core experiments, Willman et al, observed a reduction in residual oil from an initial 50-percent waterflood residual oil to as little as 8 percent after steamflooding, depending on the volatility of the crude oil. Volek and Pryor also found residual oil saturations as low as 2 percent after steam-injection experiments in waterflooded cores containing a relatively light Brea-type oil. These authors also reported low residual oil saturations in cores taken from the steamflooded part of the Brea field, averaging about 8 percent. These studies clearly indicate the potential of steam injection as a tertiary recovery process for recovering waterflood residual oil. Also, we can expect good to excellent areal and vertical sweep efficiencies when steam is injected in watered-out reservoirs, as was apparent from laboratory experiments reported by Baker. The first field-pilot test of this "steam-strip drive process" was reported by Hearn. This test was a failure, process" was reported by Hearn. This test was a failure, however, because of a poor vertical sweep efficiency. Since then, steam-strip drive has received little attention in the petroleum engineering literature. Although the precess (a combination of thermal and compositional precess (a combination of thermal and compositional effects) is rather complex, its basis seems to be sound and simple. Therefore, we conducted a laboratory study to further explore the potential of steam-strip drive as a tertiary recovery process. To direct our study we concentrated on a specific prototype reservoir and crude oil. The results obtained for prototype reservoir and crude oil. The results obtained for this reservoir served, where possible, as a starting point for more general considerations. Throughout the investigations we made extensive use of mathematical simulators. We used an existing thermal simulator for nonvolatile oil reservoirs to determine the sweep efficiencies of steam injection into watered-out reservoirs. Steam stripping and subsequent oil-bank buildup were studied with the aid of a specially developed linear, compositional, thermal simulator. Great care was taken to validate this simulator with well defined physical-model experiments. With this simulator, we physical-model experiments. With this simulator, we studied the linear displacement efficiency for various reservoir and operating conditions. JPT P. 1409
- North America > United States > California > Brea County (0.24)
- Europe > United Kingdom > North Sea > Central North Sea (0.24)
Summary Here we describe a fast 3D steam drive simulator. We use an interface model, where the single-phase steam zone is separated from the two-phase liquid zone by the steam condensation front (SCF) which constitutes the interface. Steady-state heat balances applied at the interface reduce the steam problem to a problem of gas/oil/water flow. Heat losses are treated by a prescribed conversion of steam to water. The model incorporates gravity, viscous and capillary forces and handles arbitrary permeability distributions and well configurations. We use a multigrid method to solve the pressure equation. The steam zone development is determined by a probabilistic method, which ensures that instability phenomena are properly treated. The oil/water flow problem in the liquid domain is solved as in conventional reservoir simulators. We validate the model with analytical models. Example calculations for a thin medium-viscosity oil field show that a transition zone with a reduced oil viscosity just downstream of the SCF has a pronounced stabilizing effect. This, and the global heat loss effects are the reason for the high displacement efficiency of steam drives. Introduction Steam drive models with various degrees of sophistication are available for optimal field development and the assessment of economical risks. Fast, simple models solve the heat-balance equation and use a priori assumptions on the flow field. Examples are the frontal displacement models or the extreme gravity overlay models (a horizontal SCF). Van Lookeren was the first who combined a heat balance with mass flow. His description results in a stationary development of an inclined steam condensation front. It is, however, only applicable for favorable (pseudo) mobility ratios. Limitations of simple analytical models, and the ready availability of computers led to the development of thermal reservoir simulators. Here, we describe a model that incorporates the essential features of the steam drive process but uses some assumptions to lower the computational costs. The main assumption lies in the application of steady-state heat and mass balances over the SCF to reduce the problem to the model equations of gas/water/oil flow. The essential ideas are described extensively in previous references. In these papers, we used an effective viscosity in the single-phase liquid zone. Therefore, we could only describe the steam zone expansion and not predict oil and water production. Moreover, due to the vertical equilibrium (VE) assumption, we could not deal with steam underride in a low lying high permeable layer. In this paper, we present a 3D steam drive model which includes a two-phase liquid zone and allows arbitrary injection/production well configurations. We describe the expansion of the steam zone with a probabilistic method to deal with the possible unstable nature of the displacement process. For this, the probabilistic method was extended to 3D. The main application of the model is to aid in the design and interpretation of steam drive projects. The model can be used:to describe the shape of the steam zone in three dimensions, to predict the time of steam breakthrough, to calculate the cumulative water and oil productions for each well, and to determine the relative importance of features related to the steam drive process such as steam override, viscous fingering, and steam and/or water cresting/coning in fine gridded homogeneous and heterogeneous reservoirs. Physical Model Reservoir Geometry. Fig. 1 shows a 3D representation of a tilted rectangular heterogeneous reservoir, with thickness d, width b, and length L. It is bounded by impermeable cap and base rock with constant thermal properties. The reservoir tilt can be described by two angles:the angle between the x axis and the horizontal plane, ?1 and the angle between the y axis and the horizontal plane, ?2 The flow domain ? consists of three zones:a steam zone ?s a liquid zone ?l and an upstream and a downstream transition zone surrounding the steam condensation front ?sl which separates the steam zone from the liquid zone. Injection and production occur via an arbitrary number of wells, with an arbitrary orientation in the reservoir. Initial and Boundary Conditions. The reservoir is initially filled with dead oil and irreducible water. Compositional effects can be neglected for heavy oil. We apply no flow boundary conditions to the outer boundaries of the domain ? except for the part of the cap and base rock where an outward steam flux compensates for 1D conductive heat losses (see Appendix B). The water of condensation moves along with the steam towards the steam condensation front. Injection and Production. The number, location, orientation, and perforated interval of the injection and production wells is arbitrary. Injection wells are operated at a constant rate Qs, inj temperature Ts and steam quality fs which is the steam mass fraction of the injected steam-water mixture. Production wells are operated at a constant bottomhole flowing pressure pw The Steam Zone ? s The steam zone has a uniform steam Ss residual oil S ors and water saturation Sw and a constant temperature Ts. We assume that the fluids, i.e., also steam, are incompressible and neglect their thermal expansion. Some water can stay behind in the steam zone, thus reducing the effective steam mobility. We assume that the remainder of the water of condensation, and the injected water (for fs <1) are immediately transported to the steam condensation front where it is redistributed proportional to the total velocities normal to the steam condensation front. Therefore, we only consider one-phase flow of steam and assume that Darcy's law is applicable. We incorporate a capillary pressure term to provide a mechanism that inhibits the steam from flowing from a high to a low permeable zone. We disregard the saturation dependence of the capillary pressure in the single-phase steam zone and obtain P The constant ? gives the value for the J function at some average saturation Sss. For saturations of 50%, it typically assumes values between 0.3 and 0.7.
- North America > United States > California (0.28)
- North America > United States > Texas (0.28)