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This page discusses the primary manner in which the immiscible gas/oil displacement process has been used in qualitative terms. This is the use of gas injection high on structure to displace oil downdip toward the production wells that are completed low in the oil column. In many cases, an original gas cap was present, so the gas was injected into that gas cap interval (see Figure 1 for cross-sectional view of anticlinal reservoir with gas cap over oil column with dip angle α and thickness h). In this situation, the force of gravity is at work, trying to stabilize the downward gas/oil displacement process by keeping the gas on top of the oil and counteracting the unstable gas/oil viscous displacement process. If the oil production rate is kept below the critical rate, then the gas/oil contact (GOC) will move downward at a uniform rate.
Abstract The Prudhoe Bay field, the largest oil field in North America, was brought on production in 1977 with the start-up of the Trans-Alaska Pipeline System. Initially, ultimate recovery was estimated to be 9.6 BSTB of hydrocarbon liquids with a maximum oil production rate of 1.6 MMSTB/D. However, due to a sequence of reservoir management decisions and a series of major facility additions, total ultimate recovery is now estimated to be 13 BSTB or more, a 35% increase over initial estimates. This paper discusses the various studies, technology developments, and decisions that led to the plan of development and operation of the field. Major integrated engineering studies of the surface facility systems and the reservoir displacement processes helped to optimize the reservoir management of the field. Over the course of the past twenty years, major surface facility expansions have occurred, resulting in average gas production of 7.5 Bscf/D, with most produced gas re-injected into and cycled through the reservoir's 30 Tscf gas cap; the world's largest miscible gas EOR project, which will ultimately cover nearly 60,000 acres; and manufacture of more then 80 MSTB/D of NGLs. Introduction Discovered in 1968, the Prudhoe Bay Field is a massive sandstone reservoir complex covering over 200 square miles. The "main" portion of the reservoir consists of a large oil rim overlain by a significant gas cap (m>0.6) which, together, contained over 20 BSTB of hydrocarbon liquids and approximately 46 Tscf of free and associated gas originally in place. Almost three decades of study have led to over 16 billion dollars of investments, and the field recently passed its 20th year of operation with cumulative production to date actually exceeding the original estimate of ultimate liquid recovery. Estimates of recoverable liquids have grown from 9.6 to 13 BSTB or more. Often, such reserve "appreciation" results over time due to better understanding of reservoir volumetrics and/or better than expected production performance. Increases at Prudhoe, however, are attributable to sophisticated field development which evolved from an ongoing application and enhancement of technology. Such applications have led to implementation of the world's largest gas cycling and miscible gas EOR projects, and increases in reservoir penetrations relative to the original plan of development by nearly a factor of three (Table 1). Prudhoe's development has required the simultaneous management and exploitation of a wide range of recovery mechanisms to maximize recovery. Accurate performance prediction and understanding of these mechanisms has been paramount for thre major reasons:Small changes translated to large reserve values due to the reservoir quality and size. Hence, the stakes of development decisions were large. The scale of Prudhoe's base infrastructure implied that the magnitude of investment decisions would be large and the lead times required for facility design and construction would be long. Hence, the value of being able to "look ahead" of reservoir performance with confidence was at a premium. Progressive development of a fine-tuned highly integrated facility/reservoir system steadily increased the complexity of evaluating new projects that would potentially disturb an existing balance.
Abstract. The Prudhoe Bay Field is the largest and most prolific of US oil fields. It has been the subject of intensive geologic and engineering analysis, both to determine in-piace volumes and to develop an operating pian for the field. Joint geologic and engineering studies were of critical importance in developing the reservoir description. These studies have provided the data necessary for the mathematical and computer models that have been used to develop operating plans for efficient production of the field. This paper discusses the geology of the Sadlerochit Reservoir and the studies conducted to develop an operating plan. It also overviews the unique management structure developed by the Owners of the Prudhoe Bay Unit and the actual field development and reservoir performance. Résumé. Le gisement de pétrole de Prudhoe Bay est le plus grand et le plus prolifique des Etats-Unis. I1 a fait l'objet d'études géologiques et d'ingénierie intensives dans le but de déterminer les réserves en place et de développer un pian d'exploitation. Ces études ont été d'une importance critique pour la mise au point dune description du gisement. Elles ont fourni les données nécessaires pour des modèles mathématiques et informatisés qui ont été utilisés pour élaborer une stratégie opérationnelle d'exploitation du gisement. La communication examine la géologie du réservoir de Sadlerochit et les études effectuées pour élaborer une stratégie d'exploitation. On étudie également la structure exceptionnelle de gestion mise au point par les titulaires de la concession de Prudhoe Bay ainsi que le développement réel du gisement et le comportement du réservoir. 1. INTRODUCTION (DISCOVERY AND RESERVES) The Prudhoe Bay Field is located on the north coast of Alaska and is one of the northern most oil fields in the world. Its location is shown on Fig. 1 (Eastern Arctic Slope). The Field was discovered in 1968, and subsequent drilling has confirmed that it is the largest oil and gas field in North America. It is approximately 13 miles by 32 miles (21 kmX 52 km) in area1 extent and has approximately 150 O00 productive acres (607 km*). Prudhoe Bay's initial in-place volumes were approximately 22 billion stock tank barrels of oil (3.5 X lo9 stock-tank m3) and 47 trillion standard cubic feet of gas (1.3 X 10" standard m'). Offtake is 1.5 million barrels per day (238 X 103m3/d), or approximately 18% of US oil production. Shortly after discovery, the major working interest owners recognized the benefits of operating the field as a unit. Unitization negotiations were begun in 1969. The Prudhoe Bay Unit, which is operated by ARCO Alaska, Inc., and Sohio Alaska Petroleum Company, became effective on April 1, 1977. It is one of the f
Abstract. The Prudhoe Bay Field was discovered in 1968 and is the largest ever discovered in North America. After a successful startup in 1977, the field has produced about three billion barrels of oil and is currently producing 1.5 million barrels of oil per day, or about 20% of the total United States production. Prudhoe Bay, located on Alaska's northern coast, is remote and characterized by a harsh and cold, yet fragile and treeless environment. The main facilities at Prudhoe Bay include drill sites, separation centres, a gas compression plant, a power station, a small refinery, and associated camps and office buildings. Facilities are modularized and fabricated outside of Prudhoe Bay to minimize the amount of labour to be performed on the North Slope. Modules weighing up to 2000 tons have been successfully transported by barges to the North Slope site. Activity during the next five years will be at a higher level than the past five years. Future facilities include low pressure separation, artificial lift, and waterflooding. These facilities, plus additional drilling, should increase ultimate recovery to over nine billion barrels. Arctic operations have been safely and successfully carried out by careful planning and implementation of drilling and facility design. Résumé. Le gisement de Prudhoe Bay, découvert en 1968, est le plus grand jamais découvert en Amérique du Nord. Après un bon départ en 1977, le gisement a produit environ trois milliards de barils de pétrole (430 millions de tonnes) et continue actuellement à produire 1,5 million de barils de pétrole par jour (75 millions de t/an), soit environ 20% de la production totale des Etats-Unis. Prudhoe Bay, situé sur la côte nord de l'Alaska, est isolé et caracterisé par un environnement rude et froid, ainsi que fragile et désertique. Les installations principales de Prudhoe Bay comprennent des chantiers de forage, des centres de séparation, une centrale de compression de gaz, une centrale électrique, une petite raffinerie, des locaux associés et des bâtiments de bureaux. Les installations ont été conçues et fabriquées à l'extérieur de Prudhoe Bay pour minimiser le travail effectué sur piace au North Slope. Des modules pesant jusqu'à 2000 tonnes ont été transportés avec succès par barges sur le site du North Slope. L'activité des cinq prochaines années sera supérieure à celle des cinq années passées. De futures installations comprendront la séparation à basse pression, l'ascension artificielle, et l'injection d'eau. Ces installations, plus une intensification du forage, devraient porter la récupération finale à plus de 1,3 milliard de tonnes. Les opérations dans l'Arctique ont été réalisées avec sécurité et succès par suite d'une planification soigneuse et de la mise en oeuvre des nouvelles conce