Enhanced Oil Recovery
The core of the Alberta Bakken pool at Ferguson has been brought under an EOR program aimed at minimizing the decline rate of producing wells and maximizing the proportion of the pool’s oil-in-place that can be recovered over the long term. Solution gas produced in association with the pool’s oil is reinjected in order to maintain reservoir pressure, replace the voidage created through the removal of oil, and improve the movement of reservoir oil to producing well bores.
Rationale – The Upper Bakken reservoir is an oil-saturated, near-continuous sheet, but is relatively shallow, with low reservoir pressure and no natural water drive, and is under-saturated for gas. The production characteristics of early horizontal wells drilled at Ferguson, along with careful technical study by Granite’s predecessor company, suggested the technical need and economic benefits of initiating pressure support at an early stage in the reservoir’s producing life.
DeeThree opted against the more typical approach of pumping in water (“waterflood”) in favour of gas reinjection. Unlike in waterfloods, taking advantage of the mobility of gas enables up to nine producing wells to be supported by each gas reinjection well. Low gas pricing, the high carbon dioxide (CO2) content of the solution gas at Ferguson and other technical factors provided a strong rationale for basing the EOR scheme on gas reinjection.
EOR essentials – As the illustration and graphic illustrate, the EOR scheme is conceptually simple. Natural gas is:
Following injection the gas helps to maintain reservoir pressure and increases the mobility of the oil. The goals are to mitigate decline rates in the producing wells and increase long-term oil recoveries.
Program Development – Granite’s predecessor company initiated a pressure maintenance pilot in August 2013, converting a producing well to gas injection. Initial results were very good, with sharply increased oil production in surrounding wells and mitigation of the test well group’s overall production decline.
The EOR program was expanded to three wells in 2014 and by year-end approximately 70 percent of the solution gas produced at Ferguson was being reinjected. Just prior to Granite’s founding, the predecessor company drilled the first producing well designed specifically to optimize EOR performance, being drilled into the base of the reservoir near an existing gas reinjection well, with very promising initial results.
In May 2015, two more wells were converted from producers to injectors, bringing the total to five injector wells. This activity is still part of the EOR scheme’s Phase I, focused on a 14-section area in the heart of the pool. Please click here for more information on the three EOR phases. The go-forward plan includes further conversion of mature producing wells into gas injectors to reduce capital outlays.
Effects and Benefits – The EOR scheme delivered strong results in mitigating production declines.
The gas reinjection scheme at Ferguson is:
Long-term Objectives – Granite’s over-arching goal is to maximize the value of its asset by increasing the proportion of oil-in-place that is recovered over the long term (or "recovery factor"). This objective will be achieved through the measured, capital-efficient addition of producing wells and steady expansion of the EOR program.
A modelling study concluded that the EOR scheme could well over double the recovery factor from an estimated 6.5 percent under primary production, with producing wells spaced 400 metres apart, to more than 15 percent under full EOR with 200-metre lateral well spacing. Each 1 percent increase in the recovery factor represents an additional 5 million barrels of oil, given current resource estimates.