Statoil Develops New Method for Sand Handling

Statoil has developed a new method for handling sand entrained with the oil and gas from the well reservoirs. The result is like a golden egg: Improved recovery, better safety and reduced discharges to sea.

GULLFAKS B: October 1st was a good day for the 115 offshore workers on Gullfaks B: The sun was shining and the statistics for September showed zero incidents with personal injuries, 99.9 percent regularity in operations and a production rate of 70,500 barrels of oil (11,208 Sm3).

This is an increase in production of 15,700 barrels or about 30 percent compared with Statoil's own estimates for September, and thus the highest monthly production on Gullfaks B in three years.

"The excellent results are due to the facility having been upgraded and well-maintained. We have an experienced and competent crew and, not least, a talented and well-qualified reservoir group," says platform manager on Gullfaks B, Sven R Gundersen.

The production boost on Gullfaks B is in part due to the fact that investments have been made in horizontal and long-range wells and alternating water and gas injection. And last, but certainly not least important: Investments have been made in technology and knowledge in order to handle sand production in a better and more safe manner.

Toiling with sand
Average annual sand production is one ton per sand-producing well. Sand production has consequences for safety because sand erodes the production equipment and impairs production because wells are choked if the sand rate becomes too high. Sand production is also an environmental challenge.

The goal is therefore to design more effective and safer ways of handling the sand that is entrained with the oil and gas. This enables production with a larger choke valve opening and thus recovery of more oil and gas from the reservoir without affecting safety or the external environment.

Statoil has more than 200 sand-producing wells. The reservoirs with the lowest sand strength are on the Gullfaks field, where the sandstone is so weak it crumbles if you squeeze it between your fingers. Statoil has therefore designated this field as the most time-critical in relation to improving sand handling.

"Handling sand entrained with oil and gas from the reservoirs has always been a challenge. At the same time, sand production is something we have to live with, not least here on Gullfaks," says technical adviser and head of the sand handling project in Statoil, Halvor Kjørholt.

Statoil's breakthrough occurred about two years ago after Kjørholt, in cooperation with Gullfaks RESU (resource exploitation department) and Det norske Veritas, had collected and systemized knowledge about the erosion problems, and evaluated various technical solutions on this basis.

"The goal has been to replace the guesswork related to sand production with quantifiable facts. Individual elements in the new sand handling technology are not revolutionary, but we have enough knowledge to choose solutions that enable us to produce more in a safer and more environmentally friendly manner than before," Kjørholt emphasizes. Statoil conducted a pilot test on Gullfaks A in 2001.

"In the course of a limited period of time with testing on three wells, we recovered 5 000 more barrels of oil per day without demonstrable damage to pipes, chokes or other equipment," says Jan-Magne Garnes, RESU department manager on the Gullfaks field. The extra oil is worth about NOK 30 million.

Gullfaks B was chosen as the first installation where the sand handling system was to be implemented and is currently in the process of being put into full production. The results are already very encouraging:

In the course of the running-in period in 2003 the gain from increased oil production as a result of the sand handling technology on Gullfaks A and B is estimated at about 950 000 barrels of oil. This means a value added of more than NOK 150 million, without extra costs incurred due to increased wear and tear/erosion.

Garnes estimates that Gullfaks A and C with sand handling equipment will increase production on average by about 10 percent, i.e. about 12 000 barrels per day. The investment in sand handling has thus already been lucrative both for Statoil and the State. Statoil will also test the method on other fields and started a pilot test on Statfjord B on 6 October.

From skepticism to safety
"When the sand project was launched there was a great deal of skepticism among those of us who work here every day, says the safety officer for production on the installation, Kjetil Mæland.

"But it was healthy skepticism," adds John T. Asheim, head of production and mechanical operations. "The people who work here have long experience, and they have seen how much erosion damage sand can cause."

They both feel that there is a lot of enthusiasm for the sand handling project among the employees.

"We would never have been able to complete this project without extensive and good cooperation between the land organization, the employees offshore and, not least, the safety delegate service," Garnes emphasizes.

"A project goal has been that all feedback from the employees offshore would be considered and risks assessed before the sand handling technology was employed," he adds.

"We have managed to communicate that sand handling provides good results that benefit all parties. The working environment is improved because we have installed more robust equipment and valves that are also easier to handle. We have improved safety by improving monitoring of wear and tear/erosion. In addition, production has increased considerably, which means there is good economy in the project," says Garnes.

Extends the tail
According to the plan for development and operation (PDO), which was submitted in 1981, the Gullfaks field should have been shut down long ago. Instead, new technology and increased knowledge have contributed to improved recovery and thus to a longer lifetime. This has provided substantial extra assets for both the company and the public purse.

  • Tanker no. 1,000 recently left the Gullfaks field with oil worth about NOK 120 million.

  • Oil and gas with a total value of NOK 300 billion has been recovered from Gullfaks.

  • Just one of the 30 production wells on Gullfaks B has financed the entire development of this installation.

  • The recovery rate on Gullfaks is 59 percent (of base oil reserves), but Statoil has ambitions to recover 62 percent due to new sand handling technology, among other things.

  • "The Gullfaks field is in the tail phase and we know that at some point the field will no longer be profitable. One major goal of the sand handling project has been to increase the production rate without implementing expensive sand control measures. Several wells with small reserves thus become commercially recoverable, and the recovery rate increases in that the wells can produce more before the oil rate falls below the limit for profitability. At the same time as production increases in the short term, the sand handling project contributes to extending Gullfaks' lifetime," says Garnes.