Deepwater Gulf of Mexico oil fields typically get modest ultimate recovery factors in the 10% -35% range because of challenging reservoir characteristics and high development costs. Yet the total target for Improved Oil Recovery (IOR) in deepwater (DW) Gulf of Mexico (GoM) is temptingly large, with about 44 Billion Bbl remaining oil expected to be left behind in discovered fields at abandonment. "Technical Gaps" make most IOR processes impractical in an environment of high well costs, complex reservoirs, and substantial logistical challenges. This paper describes original work done through a project funded under the Energy Policy Act of 2005 and directed by the non-profit Corporation RPSEA (Research Partnership to Secure Energy for America). The study includes a review and analysis of the performance of 83 developed DW oil fields consisting of 415 individual reservoirs. Also, data has been collected and evaluated for 15 discovered and undeveloped Lower Tertiary, Paleogene fields. The work has assessed reservoir properties, original oil in-place, expected recovery factor, volume of projected remaining oil, and the mechanisms by which oil is trapped and not produced. The analysis of performance was then used to select a group of IOR processes which could target specific trapped oil mechanisms.The results presented here are lessons learned to date on field performance, the remaining oil target for IOR, the IOR processes being considered, and the future evaluation plan. An objective of the work is to determine the "Technical Gaps" which currently prevent the economic implementation of selected IOR processes in the challenging conditions of deepwater GoM. Recommendations will be made for future Research & Development funding to address the technical gaps and to accelerate implementation of potentially high impact IOR processes. OTC 20678Although there are a range of reservoir types, fluid properties, field development methods, and reservoir drive mechanisms across a dataset this large, average numbers were derived for recovery factor and oil trapping mechanisms. The remaining or trapped oil was apportioned to mechanisms which included non-connected to wells, capillary bound, high abandonment pressure, poor sweep, and limited drive energy. Studies on a subset of fields and reservoirs were used to determine the individual percentage splits for the trapped oil mechanisms.An initial list of 79 IOR processes was reduced to a short list based on reservoir properties and the target trapped oil mechanisms. The high cost environment and technical challenges of the deepwater Gulf of Mexico translate to IOR being anything from technical breakthroughs to permit field development (i.e. increasing from 0% recovery) to artificial lift, low cost infill drilling, or water injection (Figure 1). Only twelve fields have used water injection for drive energy and reservoir sweep, and several of these fields have had limited injection volumes. Water injection is one of the short listed IOR processes and includes two low cost applications, r...
This paper was selected for presentation by the OTC Program Committee following review of information contained in an abstract subm'hd by the author(s). Contents of the paper, as presented, haw not been m i d by the OffshoreTechnology Conference and are subject to wnscti by the author(s). The matarial, as presentad, does not necessarily refled any p a i n of the Offshore Technology Conference or its offices. Electronic repmducti. distvibution, or storage oi any part oi this paper for commercial purposes without the written consent oi the Offshore Technology Conference is prohibited. Penission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abshact must contain conspicuous acknowledgment of where and by whom the paper was presented. AbstractThe Captain Field, in UK North Sea Block 13/22a, is an accumulation of viscous, high density oil which required a development plan utilizing only extended reach horizontal wells. Parallel field appraisal and facilities engineering required a close working team since during the period of 1992 to 1994 major changes occurred in the description of reservoir fluids. Oil viscosity decreased due to improvements in sampling methods which had significant impact on recommended design parameters. Other key data acquisition and field testing provided confidence in and a linking of relative permeability data and K X , , .Fluid movement in the interwell region is dominated by gravity forces where up dip injected water slumps to bottom and water coning is a dominant feature. Well spacing of around 700-800 feet are planned. Significant water will be produced, and the cost of water handling is a primary consideration when designing well liquid flow rate. In Captain Field, the optimum well offt,ake rate is found to be between 15,000 to 20,000 bpd.Development plans include a large watedood to maintain reservoir pressure at high offtake rates. The watedood will utilize only horizontal water injectors wit11 'tuned' completions.Also, careful consideration of injector placement has taken into account potential future use for polymer flooding.
Many deep-water Gulf of Mexico discoveries of the past five years are older Tertiary reservoirs including Atlantis, Tahiti, Neptune, K-2, Thunder Horse, Shenzi, Great White, Trident, St Malo, Jack and Cascade. These middle Miocene to Paleocene reservoirs are characterized by high pressure and temperature, and low natural reservoir drive energy (due to compaction and cementation). In contrast, previous production experience in younger, Pleistocene through upper Miocene, reservoirs exhibit high primary oil recovery due to significant rock compressibility and aquifer influx. The requirement for water injection to supplement reservoir drive energy, improve oil rate, and maintain oil production rates is of primary consideration in development planning for the new, ultra-deep Gulf of Mexico discoveries. Unfortunately, there is limited production experience to use as guidance. The purpose of this study is to provide a risk-based estimate of the incremental oil from water flooding for these types of reservoirs. A parametric simulation study was performed using experimental design to calculate incremental recovery from water-flooding in ultra-deep Tertiary reservoirs in the Gulf of Mexico. Experimental design matrices were generated for both primary and water flood scenarios, based on the selected uncertainty parameters. Proxy equations for both primary and water flood oil recovery were generated from the simulation results. Statistical Monte-Carlo simulation was run using the proxy equations. By comparing the simulation results for ten year production, water-flooding case yields a recovery factor about 20 per cent higher than no-injection case based on P50 estimate. Introduction Many deep-water Gulf of Mexico (GoM) discoveries of the past five years are in water depths greater than 4,000 feet and in older Tertiary reservoirs of middle Miocene to Paleocene age (yellow dots in Figure 1)1. Structural styles of these lower slope fields include compressional anticlines, turtle structures and sub-salt three-way dip closures against salt faces. Some of these reservoirs are highly compartmentalized by faulting. In this setting, rock compaction may be less important as a production drive mechanism, and aquifer support (possibly augmented by water flooding) assumes more significance. Porosity and permeability decrease is related to greater burial depth and compaction as well as temperature-related cementation. Older middle Miocene to Paleocene reservoirs in GoM are characterized by the following:Reservoirs are often at greater subsea depths: 20,000 to 30,000 ftReservoirs often have high pressure (>15,000 psi) and temperature (>180°F)Turbidite deposition was in coalescing basin floor fans, i.e. sheet sandsSeismic imaging is poor due to allochthonous over-hanging saltReservoirs are consolidated, resulting in lower rock compressibilityIncreased diagenesis in sands with volcaniclastic components results in cementation and reduced compressibilityPaleocene reservoirs often have poorer porosity (<15%) and permeability (<30 mD)Primary recovery factors are expected to be low due to the reservoir properties
Deepwater Gulf of Mexico oil fields (DW GoM) typically get modest ultimate recovery factors in the 10% - 35% range, because reservoirs tend to be small, deep, and complex. The remaining oil target for Improved Oil Recovery (IOR) is tempting large, with about 30 Billion Bbl estimated to be left in discovered fields at abandonment. Procedures on by-passed oil mechanisms analysis are based on analysis of field data compiled by Minerals Management Service, on data extracted from focused literature reviews, and on original work to analyze by-passed oil mechanisms and describe the remaining oil distribution in turbidite reservoirs of DW GoM. This paper describes a study on oil trapping mechanism, by-passed oil categories and their distributions. It is key part of study directed at recommending a select group of IOR processes for multi-million dollar research and development funding by Research Partnership to Secure Energy for America (RPSEA). The performance of 450 oil reservoirs in 83 deepwater Gulf of Mexico fields has been evaluated and characterized by geological setting, reservoir properties, and development constraints. The results have been used to estimate statistically the average oil recovery, prominent reservoir drive mechanisms, oil trapping due to structural and depositional complexity, and reservoir volume not connected to wells. The term "Trapped Oil Mechanisms" is used in this work to define the reasons for projected remaining oil in-place under current operating practices. In this paper we review the detailed assessment of several signicant reservoirs in two fields and then present the overall summary of trapped oil mechanisms for Neogene reservoirs in the deepwater Gulf of Mexico. The results of this work are being used to define IOR processes targeted at reducing the projected ROIP.
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