This paper provides the first technical review of a casing-conveyed perforating technique to fracture stimulate multiple sands in a single wellbore. This is an alternate well completion methodology to improve life-of-well economics. Two wells in Kenai, Alaska were recently completed using this system. The system consists of perforating guns mounted external to the casing and integral valves in the casing for zonal isolation. All equipment is remotely actuated without wellbore intervention. The first well was completed with 15 perforating modules and the second with 12 modules, each placed over a 1,700' (520M) gross interval. This case history recounts the installation of these completions and their subsequent perforation and fracture stimulation. Both completions are considered technical and economic successes. The casing-conveyed perforating technique was chosen for these Beluga Sand wells in an effort to improve life-of-well economics and total hydrocarbon recovery. An exhaustive characterization study of this multiple-pay environment recognized that conventional completion techniques were not adequately developing the resource. Low-quality Beluga sand bodies represent a large potential target of reserves, but the economics of conventional completion techniques never allowed this potential resource to be stimulated and properly evaluated. Use of this new completion technique meant that all pay sands, even those low-quality sands that had conventionally been ignored, could now be effectively and economically stimulated. Minifrac data, tracers, and production logs are used to evaluate the productive potential of these low-quality Beluga Sands. Introduction From 1995 to 1998, geoscientists, petrologists, and reservoir engineers undertook an exhaustive reservoir characterization study of the Beluga formation in the Kenai Gas Field. The middle and lower Beluga sands in the Kenai Gas Field are a normally-pressured 1,700' (520M) section characterized by stacked pay with highly variable pay quality. These fluvial sandstones are 5 to 30 foot (1.5M – 9M) thick. Permeability ranges from 0.01 to 3 millidarcies. Mineralogy is complex, including a high percentage of clays, volcanics, coals, and fines as described in Table 1. The framework grains for the Beluga sandstones are metamorphic rock fragments. The sandstones are bounded by discontinuous shale, siltstone, and coal beds. Formation gas is very lean (specific gravity = 0.56) with no condensate, and formation waters contain approximately 5,000 mg/l total dissolved solids. Recovery from the middle and lower Beluga formation in the Kenai Gas Field through 2001 is 51.6 BCF with estimated 260 BCF OGIP. During this reservoir characterization study, it became apparent that conventional completion techniques were not optimally developing the Beluga Sand resource. One problem with a conventional approach is "cherry picking" the best sands in a well for stimulation, which leaves a large percentage of pay unstimulated. Unstimulated sands contribute little to a well's productivity. Attempts to stimulate a higher percentage of pay dramatically increase the development cost, especially in an operating environment with limited services and infrastructure. Worse perhaps was that conventional completion techniques prohibited evaluation of low-quality Beluga sands to determine whether they could be commercially developed and added to the reserve base. These low-quality sands in the Kenai Gas Field were identified as a potential 70 BCF recoverable target if they could be commercially developed.

Management of a robust completion approach, utilizing state-of-the-art technologies, has been successfully used to stimulate multiple pay tight gas sand intervals in an environmentally sensitive area near Kenai, Alaska. Management of several unique completion techniques has demonstrated exceptional effectiveness. Previous stimulation attempts were not successful in developing the Beluga sand resource to an economic level; therefore, a comprehensive study of all processes by reservoir, drilling, completion, and service company engineers was initiated to determine the best techniques to improve recovery and financial delivery. Engineering and laboratory studies were conducted to develop a complete understanding of the Beluga sandstone reservoir composition; mechanical and chemical properties were analyzed after which an extensive project was undertaken to develop a fit-for-purpose stimulation fluid. For the well completions, a novel Casing Conveyed Perforating System (CCPS), which has revolutionized multi-zone fracturing operations, was utilized. The CCPS facilitates pinpoint stimulation of multiple pay intervals in a relatively short period of time and also improves stimulation quality, hydrocarbon recovery and life-of-well economics. Recycling of the hydrocarbon-based stimulation fluid provided an additional project enhancement. The recycling process provides a stimulation fluid with excellent rheological properties. Management of the fluid recycling process also reduces the total volume of base hydrocarbon transported and stored in environmentally sensitive areas like those in Alaska. Recycling also minimizes the equipment footprint and minimizes overall completion cost. Wells completed using these unique reservoir evaluations, CCPS, and stimulation fluid recycling techniques have been considered technical and economic successes. The Beluga Sands The middle and lower Beluga sands in the Kenai Gas Field are a normally pressured 1,700 ft. section characterized by stacked pay with highly variable pay quality. These fluvial mineralogically complex sandstones are typically 5 ft. to 30 ft. thick and bounded by discontinuous shale, siltstone, and coal beds. Formation gas is very lean (specific gravity = 0.56) with no condensate, and formation waters contain approximately 5,000 mg/l total dissolved solids. Recovery from the middle and lower Beluga formation in the Kenai Gas Field through 2001 is 51.6 BCF with estimated 260 BCF OGIP.

Three wells have been successfully drilled, cemented and fracture stimulated in the Kenai Gas Field utilizing an industry unique Casing-Conveyed Perforating System (CCPS). This revolutionary system consists of perforating guns external to the casing and integral valves in the casing for zonal isolation while fracturing. During completion operations all downhole equipment is remotely actuated without wellbore intervention. In addition, downhole sensors were run on all three wells providing monitoring of bottom-hole pressures and temperatures during cement operations, as the cement cures, during stimulation operations, and ultimately over the productive life of the well. Special characteristics of the CCPS, such as the need for precise depth control and irregular geometry, present a unique set of drilling and cementing challenges compared to conventional casing strings. For the case history wells reviewed in this paper a total of 43 perforating modules have been deployed with 15, 12 and 16 modules run in the KBU 42–7, KBU 24–6 and KBU 44–6 wells respectfully. Meticulous pre-planning by a multi-disciplinary team of professionals provided solutions to the many challenges encountered. This paper provides detailed descriptions of the three CCPS wells drilled to date in the Kenai Gas Field, including the drilling, running and cementing requirements and the solutions developed and utilized in field operations. Each of the three CCPS wells completed to date has been deemed engineering, operational and economic successes. Field / Reservoir Description The middle and lower Beluga sands in the Kenai Gas Field are a normally-pressured 1,700' (520M) section characterized by stacked pay with highly variable pay quality. These fluvial sandstones are 5 to 30 foot (1.5M - 9M) thick. Permeability ranges from 0.01 to 3 millidarcies. Mineralogy is complex, including a high percentage of clays, volcanics, coals, and fines as described in Table 1. The framework grains for the Beluga sandstones are metamorphic rock fragments. The sandstones are bounded by discontinuous shale, siltstone, and coal beds. Formation gas is very lean (specific gravity = 0.56) with no condensate, and formation waters contain approximately 5,000 mg/l total dissolved solids. Recovery from the middle and lower Beluga formation in the Kenai Gas Field through 2001 is 51.6 BCF with estimated 260 BCF OGIP. Conventional completion techniques were not optimally developing the Beluga Sand resource in the Kenai Gas Field. The CCPS was employed to improve ultimate recovery and life-of-well economics from this resource. The numerous benefits of the CCPS in this environment have been previously documented.1,2 Casing-Conveyed Perforating System Technology The CCPS was designed to improve stimulation of productive intervals by allowing individual zone stimulation in a rapid, cost effective manner. To date eight wells have been drilled and completed in North America with the locations, number of modules, maximum deviation and dogleg severity detailed in Table 2. The casing string contains integral isolation devices, perforating guns external to the casing, and methods to fire the guns and actuate the isolation devices remotely. Figure 1 shows a schematic of a portion of the wellbore in which a second interval is being perforated and the isolation valve actuated.