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Santos applies for pool IO
Pt 1 of 2: Nanushuk Oil Pool AIO for Pikka enhanced oil recovery, storage
Kay Cashman Petroleum News
Oil Search (Alaska) LLC, a subsidiary of Santos Limited, applied to the Alaska Oil and Gas Conservation Commission on April 16 to establish an Area Injection Order for the Nanushuk Oil Pool in the Pikka unit, which lies west of the central North Slope.
Basically, Oil Search (Alaska) as Pikka unit operator requested authorization and proposed rules for enhanced (water and gas) recovery and storage injection operations.
A public hearing has been scheduled for June 4 at 10:00 a.m.
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, which is expected in 2026 per Santos Managing Director and Chief Executive Officer Kevin Gallagher
Operators within a quarter mile radius of the proposed injection wells are ConocoPhillips Alaska Inc. and Oil Search (Alaska). The surface owners within a quarter mile radius of the proposed injection wells are Kuukpik Corp. and the state of Alaska.
Enhanced recovery ops Enhanced recovery operations within the Nanushuk Oil Pool, or NOP, will employ a horizontal well line drive pattern with a Water Alternating Gas 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, the application said.
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.
Description, depth to be affected The Nanushuk reservoir is a thick accumulation of deltaic shoreface deposits and is the up dip topset equivalent of the deeper water Torok formation.
The NOP is defined as the accumulation of hydrocarbons common to and correlating with the interval defined by the Nanushuk formation, between Nanushuk and Torok formation tops, from measured depths of 3,892 and 5,166 feet or 3,785 feet true vertical depth subsea, or TVDSS, to 4,985 feet TVDSS shown on the Qugruk 3 well log. (Qugruk, drilled in 2013 by partners Armstrong and Repsol, is considered the discovery well for Pikka.)
The Torok formation underlies the target reservoir Nanushuk formation and is dominantly comprised of claystones and silty shales and thick shale sequences. The formation grades from silty shales in the shallower section to shale at the base of the Torok. The shales are described in offset wells as very fine grained medium dark grey to dark brownish and greyish black. Soft to easily friable, occasionally firm. The succession is dominated by tabular to platy cuttings with very well developed laminations, and high organic content overall with layers of organic/carbonaceous material.
The fracture gradient for this sealing shale is 16.0-17.0 ppg.
Depth and thickness: 5,200 MD/5,135 TVDSS, ~250 feet TVT.
The upper confining interval is the Seabee formation, which immediately overlies the Nanushuk formation. The base of the Seabee is the shale wall facies which is a marine flooding surface composed of condensed mudstone facies deposited during a maximum transgression and creates a good regional seal.
Distant volcanism occurred during its deposition resulting in numerous bentonite interbeds. The overall Seabee formation is a thick shale/claystone dominated unit which represents the distal deep-water slope and basinal deposits.
The claystones within the Seabee are described as medium grey to dark grey, soft and mushy to slightly firm, locally partings along laminations, commonly micas and scattered very fine lithic grains. Grading to weakly fissile shale. The fracture gradient for this sealing shale is 14.9-16.8 ppg confirmed by a leak off test in well CD4-594 at 14,767 feet MD/4,059 feet TVD (16.8 ppg EMW or .87 psi/ft) and a formation integrity test in NDB-43 at 6,260 feet MD/4,323 feet TVD (14.9 ppg EMW or .77 psi/ft).
Depth and thickness: 3,175 feet MD/2,830 feet TVDSS, ~1,000 feet TVT.
The Torok and Nanushuk formations are the lower portion of the Brookian sequence and are Lower Cretaceous in age. The Lower Cretaceous section is a large-scale constructional siliciclastic clinoform system, where the topset unit is the Nanushuk formation and the foreset unit is the Torok formation.
The internal architecture of the system is comprised of multiple clinoforms, of different order, accretionary deposited from west to east. The development of the NOP in the Pikka unit contemplates the drilling of long horizontal wells across a number of different order clinoforms, per the application.
The Nanushuk hydrocarbon bearing sandstones are often present at the topset of the clinoforms and comprised of amalgamated sands gradationally changing to clay-siltstone with abundant thinly laminated mudstones.
Note: See part 2 in the May 12 issue of Petroleum News.
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