Analysis and Treatment of Formation Damage at Prudhoe Bay, Alaska
- T.N. Tyler | R.R. Metzger | L.R. Twyford
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- June 1985
- Document Type
- Journal Paper
- 1,010 - 1,018
- 1985. Society of Petroleum Engineers
- 2.4.3 Sand/Solids Control, 4.1.5 Processing Equipment, 4.3.1 Hydrates, 2.7.1 Completion Fluids, 5.1.1 Exploration, Development, Structural Geology, 4.2.3 Materials and Corrosion, 1.11 Drilling Fluids and Materials, 3 Production and Well Operations, 1.6 Drilling Operations, 3.3.1 Production Logging, 2.2.2 Perforating, 1.14 Casing and Cementing, 5.1.2 Faults and Fracture Characterisation, 5.2 Reservoir Fluid Dynamics, 1.8 Formation Damage, 1.2.3 Rock properties, 4.1.2 Separation and Treating, 3.2.4 Acidising, 4.3.4 Scale, 5.1 Reservoir Characterisation
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Formation damage, which can occur at any time during a well's history, is recognized by lower-than-expected productivity and high decline rate. At Prudhoe Bay, productivity and high decline rate. At Prudhoe Bay, investigations have shown that formation damage can be induced as a result of incompatibility of certain drilling. completion, workover, and stimulation fluids with formation water, or can occur naturally as a result of the scaling tendency of connate water with a decrease in pressure and migration of fines. In general, damage is pressure and migration of fines. In general, damage is the result of adverse fluid/fluid or fluid/formation interactions. Because of the complex nature of these interactions, effective resolution of damage problems requires the combined efforts of engineers, geologists, and laboratory personnel. A comprehensive damage mitigation program personnel. A comprehensive damage mitigation program includes both preventative and corrective actions. These efforts are directed toward optimizing the drilling investment by ensuring that a well's full capacity can be realized while using cost-effective methods.
The Prudhoe Bay field is located on the coast of Alaska's North Slope, just south of the Beaufort Sea, and about 250 miles [400 km] north of the Arctic Circle. The principle producing interval within the Prudhoe Bay field is principle producing interval within the Prudhoe Bay field is the Ivishak formation of the Sadlerochit group. The field, which was unitized by 16 working interest owners before being placed on production in June 1977, has two operators-Sohio Alaska Petroleum Co. in the west and ARCO Alaska Inc. in the east. After the first few months of field production, it became evident that the majority of wells could be placed into two categories: those with low decline rates (10 to 20% per year) and those with high decline rates (50 to 70% per year). No clear pattern emerged that could account for the high decline rates. Therefore, a concerted effort to resolve this problem was initiated in the form of a Unit Well Damage Study Group, which included engineering, geological, and laboratory representatives from the three major owners-Sohio Alaska Petroleum Co., ARCO Alaska Inc. and Exxon U.S.A. Historically, the approach to the formation damage problem at Prudhoe Bay can be divided into three phases. problem at Prudhoe Bay can be divided into three phases. Phase I was directed toward categorizing the types of Phase I was directed toward categorizing the types of damage, defining formation damage mechanisms, and evaluating various remedial treatments. During Phase 2, a fundamental understanding of the damage mechanisms was achieved, diagnostic techniques were developed to verify the kind of damage present in producing wells, and viable methods to mitigate formation damage were identified. Currently, Phase 3 includes improving operational procedures. analyzing ways to increase treatment procedures. analyzing ways to increase treatment success/failure ratios, and systematically optimizing treatment processes, thereby improving the cost-effectiveness of the processes, thereby improving the cost-effectiveness of the overall capacity restoration/sustainment programs. A geologic description of the Prudhoe Bay field has been presented previously by Wadman et al., and a history of the well damage problem was summarized earlier by Braunston. In addition, laboratory studies have been reported by Shaughnessy and Kline and Meyers, et. al. This paper describes the interdisciplinary efforts that have been applied in developing a comprehensive field program to resolve formation damage problems, with emphasis on operational practices and field results.
The Prudhoe Bay field structure was formed when the sandstones and conglomerates of the Permo-Triassic Ivishak formation, the main producing interval, were truncated near the southern flank of the Barrow Arch by the Lower Cretaceous unconformity. This unconformable surface was overlain by Lower Cretaceous marine shales. These marine shales. in conjunction with major normal faults, provide the trapping mechanism for the present hydrocarbon accumulation. The exact source of hydrocarbons remains open to interpretation. However. the latest data indicate that the hydrocarbons were resourced by the Cretaceous and Jurassic shales. The Ivishak formation has been divided into four zones on the basis of log response as a function of lithology and inferred environment of deposition. A generalized stratigraphic section, type log, and average zonal properties are illustrated in Fig. 1. properties are illustrated in Fig. 1. Zone 4, the uppermost interval within the Ivishak formation, is the most texturally uniform of the four. It is best described as a gradual fining-upward sequence of fine to lower-medium-sized sandstone with thin, interbedded, tight siltstones and shales. Bedding is typically massive, although occasional cross and ripple laminations are present, as are minor pebble-lag conglomerates. The upper present, as are minor pebble-lag conglomerates. The upper contact with the Shublik formation is unconformable and marked by a distinctive conductivity spike on the dual induction log, the effect of a large concentration of modular and disseminated pyrite. Composition is dominated by quartz, dense chert, and microporous chert. Vermicular kaolinite and subordinate illite clays occur as pore fillings and as a replacement of microporous chert.
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