By Alan Bailey
Recent 3-D seismic surveys in the Kuparuk River field on Alaska’s North Slope are enabling the identification of new drilling leads in the field, according to field operator ConocoPhillips’ latest Kuparuk plan of development that the company has submitted to the Alaska Department of Natural Resources. A survey conducted in 2005 has enabled the discovery of a number of drilling opportunities, including sidetrack wells using coiled tubing drilling, sidetracks using conventional rotary drilling, and the drilling of new wells, the plan says.
The results of another survey, conducted over 220 square miles of the western part of the Kuparuk River unit in 2011, are still being interpreted, with the results being integrated into work programs and the identification of further drilling opportunities. And in 2013 ConocoPhillips merged this survey with another survey in the southwestern part of the unit, to allow complete coverage of the area of the Shark Tooth prospect that the company is currently working on, the plan says.
Coiled tubing drilling, a key drilling technique in the Kuparuk field, involves the use of a continuous length of small-diameter, flexible drill pipe, with a motor-driven drill bit. The flexible drill pipe is drilled out from the side of an existing well bore, to form a sidetrack well that can snake its way through packages of oil-bearing reservoir sands.
The large portfolio of potential coiled tubing wells has resulted in the commissioning and contracting of a state-of-the-art specialized coiled tubing Arctic drilling rig that has been in continuous use since May 2009, the plan says.
A huge field
As one of the largest producing oil fields in North America, the Kuparuk River field has been delivering oil since the early 1980s. But, as the amount of oil remaining in the ground declines, ConocoPhillips is having to use high-tech drilling and oil recovery techniques to extract further oil from the field’s challenging, compartmentalized reservoir rocks. In May Trond-Erik Johansen, the company’s Alaska president, told the Anchorage Chamber of Commerce that 3.75 billion barrels of conventional oil remain in the field, and that there are a further 15 billion barrels of heavy oil in the Kuparuk River unit.
In 2013 field production averaged 85,700 barrels of oil per day, the plan of development says. During that year ConocoPhillips completed a 14-well coiled-tubing-drilling program that generated a peak rate of 4,520 barrels per day of incremental oil. The company also completed one conventional well, the plan says.
In 2013 the field had 466 production wells and 351 injection wells in 44 drill sites.
ConocoPhillips anticipates 13 to 17 coiled tubing sidetrack projects and eight new conventional rotary wells in 2014, the plan says.
Enhanced oil recovery
Maximizing oil recovery from the aging field involves the effective management of various techniques for enhanced oil recovery, as well as delineating areas of the field with oil accumulations that can viably be developed and then drilling appropriate development wells.
At the core of the oil recovery strategy comes waterflood, the injection of seawater and produced water into the field reservoir to sweep oil from the reservoir rock. But the alternation of waterflood with the injection of a material known as miscible injectant, a mixture of natural gas and natural gas liquids, has become the procedure of choice for enhanced oil recovery. Essentially, the miscible injectant acts as a solvent, leaching the oil from the rock pores, while the water sweeps the oil towards production wells.
The technique, referred to as water-alternating-gas, or WAG, can involve the use of either miscible injectant or immiscible dry gas. And, as the field has evolved, some drill sites have stopped using miscible injectant, and some have been converted to water injection only, the plan says. ConocoPhillips has been piloting the use of injected dry gas to retrieve from the reservoir some of the natural gas liquids that were previously injected as miscible injectant.
ConocoPhillips is also evaluating the potential use of a technique called alkali surfactant polymer, or ASP, for mobilizing oil in one of the Kuparuk sands, the plan says.
One benefit of using miscible injectant for enhanced oil recovery is the manner in which the injectant flowing towards production wells assists in “artificial lift,” a procedure whereby oil is driven up a production well by some artificial means, rather than just being forced to the surface by the reservoir pressure. Gas lift, a technique that involves flowing gas into a production well, is the most common artificial lift technique used in the Kuparuk field, the plan says. But the gas lift system cannot by itself drive oil all the way to the surface in many wells, given limitations on gas pressure and the fact that some wells are now producing fluids containing as much as 95 percent water, the plan says.
Natural gas is clearly a key material for use in oil production at Kuparuk, and is also used as a fuel for the field facilities. In the past, gas production from the field has exceeded fuel requirements, thus enabling the use of surplus gas for WAG operations, the plan says. With insufficient natural gas liquids to meet miscible injectant demand, Kuparuk has for several years been importing natural gas liquids from the neighboring Prudhoe Bay field through a pipeline called the Oliktok pipeline.
But gas production at Kuparuk is declining. So, with fuel gas being critical to field operations, ConocoPhillips has been moving ahead with a plan to convert the Oliktok pipeline for shipping gas rather than natural gas liquids from the Prudhoe Bay field. The import of natural gas liquids from Prudhoe Bay is expected to end in 2014, the plan says. As a consequence, the plan assumes that large-scale WAG with miscible injectant will also stop before the end of 2014. After that time, miscible gas injection will continue at just four drill sites, using natural gas liquids produced from the Kuparuk field, the plan says.
Because the gas from Prudhoe Bay contains 10 to 12 percent carbon dioxide and could, therefore, cause corrosion in the Kuparuk production system, this gas will simply be used as fuel gas, and will not be injected into the Kuparuk field reservoir, the plan says. Then, with indigenous Kuparuk gas that would otherwise have been used as fuel becoming available, ConocoPhillips plans to commence a full-field “lean gas chase,” using injected dry gas to recover some of the natural gas liquids trapped in the reservoir rocks, and to enhance the artificial lift in wells that produce high volumes of water.
In addition to maximizing oil recovery within the traditional reservoirs of the Kuparuk field, ConocoPhillips sees potential for exploration and appraisal leads identified from seismic surveys within the Kuparuk River unit, the plan says. The company has been moving forward with one of these opportunities, the Shark Tooth prospect, having drilled a well in the prospect in January 2012. Production results are also being evaluated, following a perforation and hydraulic fracturing pilot test in the Cretaceous Moraine interval, an oil reservoir in the Brookian rock sequence above the reservoir rocks of the Kuparuk field, the plan says.
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