A new single-well tracer method has been developed to measure residual oil saturations of watered-out formations within a precision of 2 to 3 PV percent. This in-situ method makes an average measurement over a large percent. This in-situ method makes an average measurement over a large reservoir volume by using trace chemicals dissolved in formation water. The technique is applicable in both sandstones and limestones for a wide range of conditions. Introduction Residual oil saturation is a basic item of data for many aspects of reservoir engineering. This number is required for normal material-balance calculations. Residual oil saturation is also extremely important in determining the economic attractiveness of a planned waterflood or a proposed tertiary recovery operation. Finally, in some areas proration is related to attainable residual oil saturation. Core analysis and well logging, the two most widely used methods for measuring residual oil saturations, are subject to a variety of well known limitations. One principal common fault is that both methods yield values that are averages over very small reservoir volumes. The chemical tracer method described in this paper samples a much larger volume of reservoir around a single well, The residual oil saturation measured represents an average over as much as several thousand barrels of pore space. Because this method makes an in-situ measurement, additional limitations of other methods are also avoided. In the single-well tracer technique, a primary tracer bank consisting of ethyl acetate tracer dissolved in formation water is injected into a formation that is at residual oil saturation. This bank is followed by a bank of tracer-free water. The well is then shut in to permit a portion of the ethyl acetate to hydrolyze to permit a portion of the ethyl acetate to hydrolyze to form ethanol, the secondary tracer. Finally, the well is produced and the concentration profiles of the two tracers are monitored. Ethyl acetate is soluble in both the water and oil phases, but ethanol is, for all practical purposes, phases, but ethanol is, for all practical purposes, soluble only in the water phase. As a result, the ethanol travels at a higher velocity and returns to the wellbore earlier than does the ethyl acetate. The difference in arrival times can be used to determine the residual oil saturation through the use of computer programs that simulate the tracer test (the greater the programs that simulate the tracer test (the greater the oil saturation, the greater the difference in arrival times). Field tests have demonstrated the reliability and applicability of this technique. This paper describes the tracer method, gives results of field experience, and presents a mathematical description of the process. One field application is described in detail, followed by a discussion of the scope and limitations of the technique. General Description of the Tracer Method Theoretical Basis The chemical tracer method depends on chromatographic retardation of a tracer chemical that is soluble both in formation water and in oil. Considering a system in which the oil is stationary (or at residual saturation) and the formation water is flowing at a-> velocity V w, the local velocity of a typical tracer molecule is-> -> JPT P. 211

During the late 1990's, Exxon and Mobil had each independently developed next-generation reservoir simulation systems. Both next-generation systems embodied a substantial number of step-out simulation technologies, which were extremely complementary. ExxonMobil moved aggressively to combine the best of both companies’ technologies into one industry-leading simulation system called EMpower™. This new simulation system is now being used to actively manage ExxonMobil's global resource base. Key features of this industry-leading simulator are described in this paper. The new simulator employs unstructured grids to more accurately model complex geologic features, near-wellbore flow, and aquifer support. Algorithms for optimal layering and flow-based scale-up on unstructured grids are tightly integrated in the EMpower system. The computations are performed within the unstructured grid fabric. Interactive simulation ties together the geologic and reservoir simulation models with production data yielding high-confidence forecasts of future performance. Emphasis is on minimizing the overall turnaround time between formulation of the simulation problem and generation of results. A comprehensive graphical user interface provides reservoir engineers and geoscientists of all skill levels with easy access to reservoir simulation. The user interface is designed to facilitate the full range of simulation problems—from quick screening studies to large, complex field models. The geoscience and reservoir engineer communicates to the executing simulation through the user interface, thereby allowing simulation progress/results to be monitored, paused, terminated, and/or restarted on command. Results are viewed within the user interface using spreadsheets, charts, or full 3D visualization. The object-oriented design of the new simulator is very flexible. The reservoir flow model is tightly integrated with the well and surface facility models for accurate, smoothly running simulations. Execution of complex well management strategies is specified in an intuitive, graphical format. For added efficiency, the simulator also is designed to take advantage of computing hardware that utilizes multiple parallel processors. The capabilities of this next-generation simulation system are demonstrated through a field study involving complex geologic features (e.g. non-vertical faults and stratigraphic pinchouts) and multiple reservoirs connected to a common production infrastructure. Introduction Reservoir simulator development has historically been an active area of internal research and development at both Exxon and Mobil.1–6 During the late 1990's, Exxon and Mobil each independently developed next-generation reservoir simulation systems. Both next-generation systems employed a substantial number of step-out simulation technologies, which were extremely complementary. ExxonMobil moved aggressively to combine the best of each company's technologies into one industry-leading simulation system called EMpower. This new simulation system is now being used to actively manage resources within ExxonMobil's global asset base. This paper describes the EMpower simulator and some of its key features. Potentially the most significant innovation adopted in the new simulator is unstructured gridding, with computations performed within the unstructured grid. A number of researchers have contributed to developments in unstructured gridding over the past two decades7–9. However, industry generally has been reluctant to apply this capability to practical reservoir simulation due in part to concerns about potential loss in computational efficiency.