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Part 2: Nanushuk Oil Pool AIO for Pikka enhanced oil recovery
Kay Cashman Petroleum News
On April 16, Santos subsidiary Oil Search (Alaska) LLC, or OSA, as the operator of the Pikka unit applied to the Alaska Oil and Gas Conservation Commission for an Area Injection Order to allow enhanced oil recovery in the Nanushuk Oil Pool.
Conservation Order 807, issued on July 20, 2023, defined the extents of the Nanushuk Oil Pool, or NOP, and prescribed rules for its development. OSA is now seeking authorization to conduct an EOR injection project in the NOP in anticipation of beginning production from the Pikka unit in the coming years.
Consistent with the portion of AOGCC's mission that seeks to promote greater ultimate hydrocarbon recovery, the agency approves injection orders for several purposes, including EOR, storage, and disposal either on an individual well or on an areawide basis in Alaska.
EOR injection orders establish rules for conducting operations that are intended to increase the amount of oil that could be recovered from a pool by one or more of the following mechanisms: maintaining reservoir energy, sweeping oil through the reservoir to a production well, or modifying the properties of the oil to make it more mobile.
OSA's application to AOGCC seeks endorsement and authorization for enhanced oil recovery (water and gas) and storage injection operations.
According to the application, a water injection pulse test is planned for June to confirm connectivity between wells and expected waterflood response. Well tests are being conducted to optimize development plans. And storage avoids risks associated with hauling fluids to a non-Santos operated facility prior to field startup.
Storage of produced oil from initial development well tests, the application said, will prevent waste prior to full field startup of Pikka Phase 1 which is expected in 2026 per Santos Managing Director and Chief Executive Officer Kevin Gallagher.
Proposed EOR ops Enhanced oil recovery operations within the NOP will employ a horizontal well line drive pattern with a Water Alternating Gas ("WAG") or rich gas flood, to enhance oil recovery from the reservoir. Due to the highly laminated nature of the reservoir, all the wells (including injectors) will be hydraulically fracture stimulated to enhance productivity and improve vertical injection sweep.
Additionally, to remove potentially damaging fracturing gel and confirm rate capacity, frac flowbacks will be conducted; and accompanying oil production from the wells will be re-injected into the reservoir prior to startup to prevent waste.
Only pre-production test fluids recovered beyond the initial load recovery will be re-injected, with volumes and injection pressures being tracked to ensure fracture gradients are not exceeded. For flexibility in dispersing pressure, test fluids may be injected in both producers and injectors which have been previously hydraulically fractured.
Mechanical integrity of injectors Surface holes will be drilled and set above the Tuluvak formation for proper anchorage, prevention of uncontrolled flow, and protection from permafrost thaw and freeze back.
In the Pikka area there are some known areas of shallow gas within the Tuluvak formation, so top-setting the Tuluvak will allow blowout prevention equipment to be installed prior to drilling the gas-bearing formation. This casing setting depth provides adequate depth for required kick tolerance to drill the intermediate section.
Within the planned development area, the base of permafrost is interpreted to be between 750 feet and 1,400 feet TVDSS, or true vertical depth subsea.
The blowout prevention equipment will be installed and tested in accordance with 20 AAC.25.035 requirements. A formation integrity test will be performed in accordance with 20 AAC 25.030(f).
Intermediate sections will be drilled utilizing the latest directional techniques from surface casing, encountering the top of the Nanushuk at 40-85 degree inclination. Casing will be set and cemented with the shoe just above, or just into, the Nanushuk reservoir and containment will be verified with a bond log.
The Tuluvak will be cemented where gas is present. A gas-tight liner top packer will provide secondary containment above with the surface casing cement as additional protection against gas movement. The section between the Tuluvak and the top of the Nanushuk reservoir consists primarily of mudstones and siltstones with no significant hydrocarbon zones. See figures 5 and 6 for a sketch of a typical producer well design for the first injector completed in the NOP, NDB-43.
Storage operation The storage operation will involve re-injection of NOP crude oil, solution gas and minor amounts of water recovered from well tests prior to facility startup.
Seawater with alternating gas-injection is proposed for enhanced recovery injection into the NOP. After water-breakthrough, individual well patterns may be swapped to produced water.
Injection history at the Colville River unit has demonstrated the compatibility of both produced water and seawater in Brookian age reservoirs, specifically the Nanushuk formation at the Qannik pool, over the past 10+ years.
No issues are expected with injection of either seawater or produced water/gas into the Nanushuk formation. Liquid injection rates between 2,000 and 10,000 barrels per day and gas rates between 3 million and 15 million standard cubic feet per day are expected at each injection well drilled for the project and will be managed to achieve and maintain a voidage replacement ratio of 1.
AOGCC will hold a public hearing on OSA's application on June 4.
--KAY CASHMAN
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