Nitrogen lift continues at 88 Energy's Project Icewine

Nitrogen lift was continuing at Project Icewine, 88 Energy said on Friday, as it updated the market on its projects located on the North Slope of Alaska.

The AIM-traded firm said that as at 1730 Alaska time on 21 June, the flowback rate at Icewine#2 was 50 barrels of water per day on a variable choke setting.

Wellhead pressure had been managed lower to 75psi to reduce back pressure in the system.

“Since the last update on 18 June, adjustments were made to the flowback system to determine the optimal settings for the nitrogen lift operation,” the board said in its statement.

“Consequently, flowback rates fluctuated between an average rate of 50 barrels of water per day to 120 barrels of water per day.”

The company said the percentage of hydrocarbon gas in the flowback dropped to 5% at one stage due to an increased nitrogen injection rate - 300 scf/m - which was deemed to have limited the flowback of both water and gas from the borehole.

“The reduction in productivity is attributed to an effective downhole choke created between the 4.5" annulus and the 1.75" velocity string, limiting the flowback when the nitrogen rate is too high.

“The nitrogen injection rate is now being reduced back to 150 scf/m and should result in an increase in flowback of water and gas from the borehole.”

During the period, there had been “no meaningful change” to the composition of the returned gas and fluid, 88 Energy said, adding that flowback was considered to be 100% stimulation fluid and gas.

Hydrocarbon gas content continued to be predominantly methane at 90%, with some heavier elements up to trace C6+.

The composition and rate was as expected for the current stage of the flowback, 88 Energy claimed, and results were considered unrepresentative of the hydrocarbon composition in the reservoir, as the well was still in clean-up phase.

Salinity measurements of the flowback fluid were also not indicative of connectivity to the reservoir, as expected at the current stage of clean-up, it added.

“Total clean up fluid returned since commencement of flowback on 12 June, net of diesel for freeze protection and any other fluids introduced as part of the current operation, is 1,100 barrels interpreted as 100% stimulation fluid.

“Total fluid returned for the entire Icewine#2 flowback operation, including last year, is now 6,632 barrels or 24% of the frac fluid injected vs a target percentage return of at least 30%.”

The Icewine#2 well is located on the North Slope of Alaska, with 88 Energy - via its wholly-owned subsidiary Accumulate Energy Alaska - having a 77.55% working interest in the well.

The well was stimulated in two stages over a gross 128-foot vertical interval in the HRZ shale formation, from 10,957-11,085ft TVD, using a slickwater treatment comprising 27,837 barrels of fluid and 1,034,838 pounds of proppant.

Prior to the 2017 winter shut-in, 20% of the stimulation fluids had been flowed back compared to a projected minimum target of 30% to gain connectivity to the source rock reservoir.

Flowback re-commenced, on schedule, at 2230 Alaska time on 11 June, to clean-up stimulation fluids from the Icewine#2 borehole with a well head pressure of 3,000 psi and flowback rate of 253 barrels of water per day on an 8/64" choke.

A production log was run on 12 June, 88 Energy reported, which confirmed that all perforations were contributing to flow.

As per the flowback design, nitrogen was then introduced gradually to the wellbore from 0845 Alaska time on 13 June, prior to the installation of the coiled tube velocity string, to artificially lift stimulation fluids in order to gain connectivity to the reservoir.

The flowback rate stabilised at 200 barrels of water per day through an 8/64" choke, and then steadily declined to circa 100 barrels of water per day, as per expectation.

“Flowback was interrupted, as per the programme, on 15 June at 0800 Alaska time, to allow installation of the velocity string,” 88 Energy explained.

“Flow was re-established on 15 June at 2000 Alaska time with nitrogen introduced into the annulus between the 4.5" casing and the 1.75" velocity string.”

After displacement of fluid in the annulus, the flowback rate stabilised at 350bpwd through a variable choke to maintain a target wellhead pressure of 200-400psi.

“This technique decreases the backside pressure in the system and optimises lifting of fluid from the wellbore.”