Prudhoe holding steadyDecline in oil production from the unit has now been halted for three years Alan Bailey Petroleum News
Despite the challenging oil price environment, production from the Prudhoe Bay unit on Alaska’s North Slope has held steady for a third year, rather than continuing the production decline that had previously marked the field’s performance, executives from BP Exploration (Alaska), the field operator, have told Petroleum News. The sustained Prudhoe Bay production presumably provided a solid base for increased oil throughput in the trans-Alaska pipeline in 2017.
Prudhoe Bay data for 2017 have yet to be finalized, but preliminary figures show an average production rate of just over 280,000 barrels of oil per day. That compares with 281,800 bopd in 2015 and 280,700 bopd in 2016.
The historical production decline rate would have resulted in a figure closer to 260,000 bopd in 2017, said Scott Digert, BP Prudhoe Bay subsurface manager. Digert attributed the Prudhoe Bay performance to the efforts of the Prudhoe Bay workforce in improving operational efficiency in the field, rather than to any particular characteristics of the field itself.
“It’s a tremendous performance,” Digert said. “What we’re really happy about is that that has been done, not through the physics of the field, but through human endeavor.”
Operational efficiency A key factor in the field performance is the operational efficiency, the extent to which the production uses the available capacity of the production facilities. Sustained, high operational efficiencies drive steady-state production, with laminar fluid flow enabling more material to move through the systems, explained Jennifer Starck, Prudhoe Bay production manager. The efficiency has climbed steadily from a level around 79 percent in 2014 to around 85.3 percent in 2017, she said.
Achieving such a high level of operational efficiency in a field system as complex as Prudhoe Bay is a major achievement, Digert said. The Prudhoe Bay unit moves 8 billion cubic feet of gas, 1.5 million barrels of water and 300,000 barrels of oil each day though seven processing facilities and two major gas plants. There are 1,800 well penetrations in multizone reservoirs.
“To keep all of that running at an 85 percent efficiency is pretty remarkable,” Starck said.
Active wells One key factor that overall efficiency is the number of active wells in the field. The more wells available for use, the greater the possibility of swapping wells out to allow some wells to recover, and the easier it becomes to maintain maximum production from the field. While two years ago there were about 650 active wells, in 2017 that number increased to nearly 750. Having around 630 to 650 wells online at any one time will fill the field facilities, Digert said.
Achieving this high active well count has involved around 500 production related, non-rig well work jobs over the course of 2017, a figure up from around 430 in 2016 and 465 in 2015. Well work typically involves entering and re-perforating an existing well bore. In one particularly effective project, for example, re-perforating a well relatively high in the well bore has resulted in new production of gas rich in natural gas liquids, a gain equivalent to the drilling of a new well at a fraction of the cost.
BP also continues drilling into reservoir areas where untapped pockets of oil remain. The company has been using data from a new 3-D seismic survey in the north Prudhoe Bay area to identify new drilling targets.
New production in the northern area has boosted throughput in the Lisburne Production Center, pushing production in that facility from 23,000-25,000 barrels per day a year and a half ago to 40,000 bpd in 2017, Digert said.
Maintenance efficiency Although there are days when the high number of active wells enables operational efficiency to approach 100 percent, the need to take equipment out of service for maintenance dilutes the efficiency level over the course of a year. But the efficient planning and execution of maintenance work can minimize maintenance impacts on production without compromising safety.
For example, 2017 saw a major maintenance “turnaround” at Gathering Center 1, one of the hub facilities in the unit. Rigorous planning for this complex project had started two years earlier. The project was completed a week ahead of schedule, with no safety incidents, Starck said.
Work culture Another factor in improved efficiency has been a change in work culture introduced in 2016, in which people are now identifying work that really needs to be done, rather than automatically continuing traditional jobs, or doing what people want to do without necessarily questioning the benefits. The result in 2016 was a smaller work program that delivered world class results in terms of value to the business, Starck said.
Digert commented that in 2017 the work program expanded but became more efficient, focusing on work simplifications and quickly stopping jobs that were not delivering results. A key is to progress a number of relatively small, efficient jobs, rather than chase elephants, he said. He also commented that science projects have been cut, unless projects deliver value. And projects such as the use of different types of enhanced oil recovery must be justified in terms of cost benefits.
Team structure Another key change at Prudhoe Bay has been a move from an organization based on functions such as reservoir engineering and production engineering, to a team structure, with one team for each main production facility, Digert said. The field operations manager for a facility is aligned with a reservoir management team in Anchorage. Each team then acts as a business, seeking efficiencies in its sector of the unit and able to make quick decisions over operational improvements. A team takes ownership of the profitability of its sector of the field.Interconnected facilities But the teams also operate cooperatively with each other, seeking ways to improve field performance as a whole. This is particularly important, given the manner in which facilities in different parts of the unit are now interconnected, allowing production fluids to be moved from one facility to another, to make optimum use of all of the facilities. For example, in one situation it proved possible to alleviate production constraints in the Lisburne Processing Center by shuttling some production to Gathering Center 1, where there was available capacity. That improved efficiency at Gathering Center 1 while also opening up space in the Lisburne facility, thus enabling some shut-in wells at Lisburne to come back on line.Extending field life A question now is how to continue to viably and safely extend the life of the oil field. So far about 12 billion barrels of oil have been produced from the field and another 10 billion barrels remain in place. With the economics of producing additional oil being marginal, the operating efficiency now being achieved is critical to flattening the production decline at a $50 oil price, with well work proving especially profitable, Digert said. The current operations are viable at current oil price levels, he said.
And improved efficiency at Prudhoe Bay has resulted in oil production gains equivalent to bringing a new North Slope oil field on line annually, Digert said.
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