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Abstract Understanding reservoir behavior is the key to reservoir management. This study shows how energy modeling with rapid material-balance techniques, followed by numerical simulations with streamlines and finite-difference methods, aided understanding of reservoir-flow behavior. South Rumaila's long and elongated Zubair reservoir experiences uneven aquifer support from the western and eastern flanks. This uneven pressure support prompted injection in the weaker eastern flank to boost reservoir energy. We learned that aquifer influx provided nearly 95% of the reservoir's energy in its 50-year producing life, with water injection contributing less than 5% of the total energy supply. The west-to-east aquifer energy support is about 29:1, indicating the dominance of aquifer support in the west. Streamline simulations with a 663,000-cell model corroborated many of the findings learned during the material-balance phase of this study. Cursory adjustments to aquifer properties led to acceptable match with pulse-neutron capture or PNC-derived-time-lapse oil/water contact (OWC) surfaces. This global-matching approach speeded up the history-matching exercise in that performance of most wells was reproduced, without resorting to local adjustments of the cell properties. The history-matched model showed that the top layers contained the attic oil owing to lack of perforations. Lessons learned from this study is that the material-balance work should precede any numerical flow-simulation study because it provides invaluable insights into reservoir-drive mechanisms and integrity of various input data, besides giving a rapid assessment of the reservoir's flow behavior. Credible material-balance work leaves very little room for adjustment of original hydrocarbons in place, which constitutes an excellent starting point for numerical models. Introduction Before the advent of widespread use of computers and numeric simulators, material-balance (MB) studies were the norm for reservoir management. In this context, Stewart et al. (1954), Irby (1962), and McEwen (1962) presented useful studies. Most popular MB methods include those of Havlena and Odeh (1963), Campbell (1978), and Tehrani (1985), among others. Pletcher (2002) provides a comprehensive review of the available MB techniques. In the modern era, classical MB studies seldom precede a full-field numeric modeling, presumably because MB is implicit in this approach. Nonetheless, we think valuable lessons can be learned from analytic MB studies at a fraction of time needed for detailed numeric modeling, preceded by geologic modeling. Of course, the value and amount of information derived from a multicell numeric model cannot be compared to a single-cell MB model. But, an analytic MB study can be an excellent precursor to any detailed 3D modeling effort. Although this point has been made by others (Dake 1994, Pletcher 2002), practice has, however, lagged conventional wisdom. In this paper, we attempt to show the value of a zero-dimensional MB study prior to doing detailed 3D numeric modeling, using both streamline and finite-difference methods. Streamline simulations speeded up the history-matching effort by a factor of three. However, we used the finite-difference approach in prediction runs for its greater flexibility in invoking various producing rules. Initially, the MB study provided key learnings about gross reservoir behavior very rapidly. In particular, energy contributions made by different drive mechanisms, such as uneven natural water influx and water injection, were of great interest for ongoing reservoir-management activities. Estimating in-place hydrocarbon volume and relative strength of the aquifer in the western and eastern flanks constituted key objectives of this study segment. Following the MB segment of the study, we pursued full-field match of historical data (pressure and OWC) with a streamline flow simulator to take advantage of rapid turnaround time. Thereafter, prediction runs were made with the finite-difference model to answer the ongoing water-injection question in the eastern flank of the reservoir. We learned that water injection should be turned off for improved sweep, leading to increased ultimate oil recovery. In addition, the numeric models identified the presence of remaining oil in the attic for future exploitation.
- Europe (0.93)
- North America > United States > Texas (0.93)
- Asia > Middle East > Iraq (0.64)
- Energy > Oil & Gas > Upstream (1.00)
- Water & Waste Management > Water Management > Lifecycle > Disposal/Injection (0.96)
- North America > United States > Wyoming > Madison Formation (0.99)
- North America > United States > Texas > Fort Worth Basin > Overall Field (0.99)
- Europe > United Kingdom > North Sea > Northern North Sea > East Shetland Basin > Block 3/8 > Ninian Field > Brent Group Formation (0.99)
- (18 more...)
- Reservoir Description and Dynamics > Reservoir Simulation (1.00)
- Reservoir Description and Dynamics > Improved and Enhanced Recovery > Waterflooding (1.00)
- Management > Professionalism, Training, and Education > Communities of practice (1.00)
- Data Science & Engineering Analytics > Information Management and Systems > Knowledge management (1.00)
Abstract Short-term pressure transient testing is gaining increased acceptance as an attractive alternative to conventional transient well testing, since the latter usually requires long flow and shut-in periods in order to meet test objectives. Unfortunately, current industry drivers are focusing on short, cost-effective, and environmentally friendly test procedures _ especially in exploration wells in deepwater and arctic environments where conventional tests may be prohibitively expensive or not feasible logistically. While various short-term tests, test procedures, and interpretation methods are available for conducting successful short-term tests, clarity is lacking for specific applications of these methods. Some of these tests include surge testing, closed-chamber testing, slug testing, underbalanced perforating and testing, and back-surge perforation cleaning. This paper provides comprehensive evaluation of general closed-chamber tests, including general surge tests, and their comparison with special tests such as, FasTest,™ Impulse™ test, and slug tests. For each of these techniques, the review will examine:Test design, testing procedure Theoretical background of each of these techniques Method of data analysis including comparisons based on both theoretical and practical considerations to determine the expected reliability, accuracy, and ease of analysis. A large portion of the paper is devoted to field examples. Several field cases are analyzed using the various techniques, and results are tabulated and presented. Analyses of these examples are presented in significantly more detail to compare the many techniques available to analyze the well-testing data obtained from surge testing, closed-chamber DST, slug testing of oil wells, underbalanced perforating and testing, and back-surge perforation cleaning. Introduction The recent technological advances in pressure and temperature gauges, surface and downhole electronics, downhole tool assembly, and data transmission have collectively paved the way for better design and, more importantly, field execution of short-term tests. Some of these tests may last for time periods as short as a few minutes, however producing very reliable estimates of reservoir properties. Techniques developed for analysis of these tests rely on modem gauge capability for accuracy and quick measurement of pressure change with time as well as accurate compensation for the effect of temperature. These methods have been well documented in the literature and include short-term tests such as:DST Slug test General closed-chamber test (CCT) Surge Test Shoot-and-pull" test, which is similar to the backsurge test FasTest (essentially a surge test/CCT) Impulse Test (also essentially a surge test/CCT). All the above tests with the exception of the slug test are similar in nature in the sense that fluid flows into a limited volume chamber where an increasing back pressure causes the influx from the formation to decline. The rate decline can be very fast and is difficult in many instances to calculate. In many of these tests it is practically imposible to distinguish the flow period from the build up period. This dictates the development of specialized techniques that accounts for this test characteristics. In a slug test, however, the fluid flow is not against atmospheric pressure but against increasing hydrostatic head as fluid accumulation takes place. It is usually possible to calculate the production rate from the reservoir into the wellbore, and hence allows for the use of classical analysis techniques. This paper provides comprehensive evaluation of general closed-chamber tests, including general surge tests, and their comparison with special tests such as FasTest, Impulse and slug tests. It also attempts to provide practical considerations of the various tests and analytical techniques to determine the expected reliability, accuracy, and ease of analysis.
- Europe (0.67)
- North America > United States > Texas (0.46)