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April 2018

Vol. 23, No.15 Week of April 15, 2018

AOGCC approves Meltwater water injection

Commission agrees that production technique change will increase oil production from the ConocoPhillips field in Kuparuk River unit

Alan Bailey

Petroleum News

The Alaska Oil and Gas Conservation Commission has issued an area injection order allowing ConocoPhillips to inject seawater and produced water into the oil reservoir for the Meltwater satellite oil field in the Kuparuk River unit. ConocoPhillips has said, and the commission agrees, that water injection will increase the ultimate recovery of oil from the field.

Currently ConocoPhillips injects natural gas into the reservoir to encourage oil production. However, this has resulted in an increasing gas to oil ratio in the produced fluids. In addition to impacting the oil production at Meltwater, a test performed in 2017 showed that the high ratio has been causing the backing out of 900 barrels per day of production elsewhere in the unit, the commission said in its order.

Meltwater produces from the Bermuda interval in the Seabee formation, a part of the Brookian sequence, the youngest of the North Slope petroleum bearing rock sequence. The Kuparuk River field itself produces from sands within the older Beaufortian sequence. The Bermuda sands at Meltwater have relatively low permeability.

Development history

When production from Meltwater began in 2001 ConocoPhillips used alternating water and gas injection to boost oil production. Initially, miscible injectant, a mixture of natural gas and natural gas liquids, was used for artificial lift in the production wells. However, in 2009 water injection ceased because of corrosion problems in the water line to the field - replacement of the line was deemed unacceptably expensive. Instead ConocoPhillips started using miscible injectant for enhanced oil recovery, a technique which the company said was the best means of maximizing production at that time.

At that point, with ConocoPhillips having no further plans for water injection, water was no longer authorized as an injection fluid for the field.

Indications of leakage

During the period of water injection, ConocoPhillips observed increased pressures in the outer annuli of three wells, but no conclusive reason for this anomaly was determined. However, in 2012 subsurface features identified from seismic data appeared to offer a potential route for miscible injectant to leak into the well outer annuli. ConocoPhillips implemented measures to contain this problem.

In 2015 AOGCC approved the injection of water into the Meltwater reservoir for specific purposes, for surveillance, logging, formation displacements near wellbores and well maintenance.

The miscible injectant used at Meltwater was delivered through a gas line from the Kuparuk River unit Central Processing Facility 2. However, in 2014 ConocoPhillips stopped importing miscible injectant into the Greater Kuparuk Area - at that point gas injection replaced miscible gas injection at Meltwater.

Given the emerging issues arising from continuing gas injection, ConocoPhillips now wants to switch to water injection by converting the gas line to Meltwater, between the Meltwater pad and the Kuparuk 2N pad, for the carriage of water.

Can only inject one fluid

In its application to AOGCC for water injection approval, the company said that, with only one functional injection pipeline to the Meltwater pad, only one fluid at a time can be injected into the field reservoir. ConocoPhillips plans to inject water at a lower pressure than was used for the original water and gas injection in the field - maintaining the injection pressure below the fracture pressure of the reservoir and the reservoir overburden helps ensure continued containment of fluids in the reservoir, ConocoPhillips told the commission.

Modeling has indicated that low pressure waterflood will increase ultimate oil recovery by 1 to 2 percent, ConocoPhillips told the commission. Moreover, the potential to recycle injection water through the Meltwater production line can prevent the production line from freezing, as production rates decline. The use of water injection should extend field life by five to 10 years. The AOGCC also commented that the reduction in the produced gas to oil ratio from the use of water rather than gas injection could result in the field reservoir becoming a more appealing target for further drilling.

And, although miscible injectant use is being restored in the Greater Kuparuk Area, to pursue newly drilled targets, the previous injection of miscible injectant into the Meltwater reservoir has rendered further use of the material in the field relatively inefficient in terms of production enhancement.





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