AOGCC approves Northstar gas injection
Hilcorp plans to start injecting gas into the Kuparuk sands to push up oil production from that part of the Beaufort Sea field
The Alaska Oil and Gas Conservation Commission has approved Hilcorp Alaska’s request to allow the injection of natural gas into the Northstar field’s Kuparuk oil pool for enhanced oil recovery. In its order, issuing the approval, the commission said that reservoir modeling showed that gas injection would result in a substantial enhanced oil recovery benefit; that the maximum injection pressure would be well below a level that might cause fractures in the subsurface rocks; and that there are no underground drinking water sources that might be impacted.
The Northstar field is operated from a gravel island offshore in the Beaufort Sea, with the unit straddling state nearshore waters and waters of the federal outer continental shelf.
Since production started in 2001 oil has come from a reservoir in the Ivishak formation, equivalent to the main reservoir of the Prudhoe Bay field. However, in 2006 BP, the then field operator, began testing production from the shallower Kuparuk sands. Sustained Kuparuk production began from a single well, the NS-08, in 2010.
Four production wellsHilcorp continues to produce oil from the Ivishak but now produces from Kuparuk sands through four wells, the NS-08, the NS-13, the NS-15 and the NS-18. There are two Kuparuk sand units involved: the Kuparuk A and the Kuparuk C, with the C sands lying above the A sands and the sands appearing to be pressure isolated from each other. The A sands contain a gas-condensate cap over an oil rim, while the C sands only contain gas condensate. The sands lie in a four-mile by two-mile, east-southeast to west-northwest trending, faulted anticline.
To date, gas produced from the Kuparuk has been injected into the Ivishak for enhanced oil recovery. In fact, this injection of gas into the Ivishak has restored the reservoir pressure in the Ivishak to a level close the reservoir’s original pressure. This phenomenon has in turn resulted in an increase in the proportion of oil to water in production from the Ivishak, Hilcorp has told the commission.
Opportunity for gas productionBut now, with more than enough gas being produced to support Ivishak production, the opportunity has arisen to start injecting gas into the Kuparuk, to increase Kuparuk oil production. Initially Hilcorp plans to convert the NS-18 for Kuparuk gas injection, but there may be further developments in the future involving the drilling or sidetracking of new wells.
The peak gas injection rate could reach 120 million cubic feet per day, with individual wells injecting at rates between 50 million and 80 million cubic feet per day. Primary oil recovery from the Kuparuk is estimated at 9 million barrels. Gas injected at a rate of 50 million cubic feet per day could elevate oil recovery to 13 million barrels, while injection at 80 million cubic feet per day could result in recovery of 14.6 million barrels, Hilcorp has estimated.