Canadian Natural Resources Dewatering Procedure Using High Pressure Methane

Prepared by Sam Hajar, Production Technologist– Canadian Natural, St. Albert District

Canadian Natural Resources Limited (Canadian Natural) has taken a common industry practice and adapted it to meet its’ current business needs. The company has modified the established process of dewatering gas wells utilizing nitrogen gas. In order to reduce servicing costs Canadian Natural has decided to use methane gas to dewater wellbores that have a history of hydrostatically loading with produced liquids.

The theory of using compressed gas to enhance gas well production has been in place for many years. Traditionally the gas used has been nitrogen which is transported to the well site in pressurized gas cylinders. Canadian Natural has modified the procedure, utilizing methane gas instead.

The process simply uses methane gas, which is transported in pressurized gas cylinders to the well site, where the gas is then injected into and circulated down the wellbore displacing any existing wellbore fluids out of the well. Alternative uses have also been identified, which include the cleaning of pipelines and chemical treatments on flowing gas wells.

The idea of using methane gas was originated by a collaboration of both contract and company employees in an effort to minimize operating costs, while endeavoring to meet or exceed gas production targets.

Liquid Loading of Gas Wells

A common problem with low pressure, low producing gas wells is liquid loading. The rate at which a well starts to load up depends on downhole pressure and tubing diameter. Theoretically wells require a critical gas lift rate of approximately 7-10 e3m3/day if tubing size is 60.3 mm. If rates drop below these rates a gas well can begin to experience liquid loading, to the point where the hydrostatic head of the fluid is greater than the bottomhole pressure. The typical end result being that the well is unable to lift gas to surface.

Gas Lift Procedure Using Kickaround Trailer (Gas Unit)

A practice still used today by many producers to solve the problem of liquid loading is to purge the wellbore clean of any fluid by circulating nitrogen gas down the wellbore and catching any fluid at surface in a container or tank. In an effort to reduce costs and eliminate the need to subsequently purge nitrogen from the system, Canadian Natural has replaced the nitrogen gas with methane gas. In order to use the gas lift methodology, the tubing string and the casing must be in communication with each other. The gas is then injected into and circulated down the tubing, causing the fluid to circulate up the casing to surface. This same procedure can be reversed to circulate the methane gas down the casing and up the tubing. Either circulating procedure will work. By eliminating the fluid out of the tubing string, the well will have a better chance to produce gas. The methane gas is transported to the well site in cylinders connected to support equipment; all mounted on a trailer towed by a truck (referred to as a “Kickaround trailer”) or alternatively on a flat bed four-wheel drive truck (referred to as a “Kickaround unit”). As the job function of both is identical, the terms may be interchanged throughout this discussion. Canadian Natural continues to look for new uses for the kickaround unit, as it has become a significant part of Canadian Natural’s daily operations.

Evolution of the Kickaround Unit

The original idea to build a Canadian Natural operated kickaround unit for dewatering gas wells, rather than using a third party, was initially proposed by a Canadian Natural contract operator in order to reduce well cleanout costs and improve efficiency. The idea was further developed with the collaboration of other Canadian Natural employees from various disciplines. The process has evolved to the point of the unit be used in other applications in addition to dewatering low pressure gas wells. Further applications identified to date include performing chemical squeezes on wells and displacing and pigging stagnant pipelines, and are discussed below.

The first prototype, although effective, had issues with mobility and capacity. A second generation unit was then built, which took into consideration weather conditions and typical lease road conditions in Northern Alberta. The second generation kickaround trailer was designed to accommodate more gas bottles and was housed in a livestock trailer, however there continued to be limitations related to the unit’s inability to access leases with poor ground conditions . In the current unit the trailer/truck combination has been replaced with a flatbed four wheel-drive truck carrying the gas cylinders and all necessary support equipment (see Figure 1).

The gas cylinders mounted on the Kickaround unit are refilled and charged by a small fill station which utilizes a 95 HP compressor (see Figure 3). The fill time with the first and second generation kickaround trailers was upwards to eight hours. With the 3rd generation unit, the fill station compressor was also upgraded and now the fill times are less than 30 minutes.

The idea and evolution of these Kickaround units are the direct result of collaboration between Canadian Natural’s field and operations staff.

Operational Benefits of Using Kickaround Unit.

1) Using methane gas to dewater low pressure gas wells allows the methane gas to be recovered down the pipeline. Previously nitrogen would have to be purged from the well, as nitrogen gas is not combustible.

2) Canadian Natural has many compressor stations in Alberta, BC and Saskatchewan making replenishing the gas cylinders simple.

3) Dewatering with the Kickaround unit reduces swabbing costs significantly.4) Pipeline pigging operations take less manpower and time because of the high

pressure gas on the Kickaround unit can physically move a pig a long distance in a relatively short period of time. This ultimately reduces labour costs and downtime.

5) Low producing gas wells, which previously could not pay out swabbing or reactivation costs can be put back on production for a fraction of the cost.

6) Chemical treatments on low producing wells now have a more attractive payout due to eliminating the high cost of a third party pressure unit.

Downhole Views

Below are two examples downhole configurations required in order to utilize the Kickaround unit for dewatering. It is important to note that the flow direction, although shown as uni-directional in the examples, the methane gas can go either down the casing or up the tubing (as depicted below) or reverse circulated down the tubing and up the casing.

Equipment

In addition to the two prototype Kickaround units constructed in 2007, Canadian Natural has formed an alliance with Flo Solutions who has built and operates two units featuring the four wheel-drive / flatbed design. These units are each equipped with 26 gas cylinders capable of holding a total of 900 m3 of gas at approximately 18300 kpa. The bottles are filled with a compressor located at a Canadian Natural compressor station. The compressor is capable of filling the gas bottles in approximately 30 minutes. The ability to fill the bottles in short period of time allows for the units to be used in multiple applications in one day. The units are hooked up to the compressor with a high pressure hose rated for 30000 kpa. At the well, the unit is connected to the wellhead, once again using a high pressure hose. The bottles are connected in series to allow for gas to flow freely through a manifold from any or all the bottles. Typically each shallow well will use approximately 6-8 bottles to unload a gas well of any wellbore fluid. It should be noted the bottles can be filled at any compressor station however the fill pressure is limited to the discharge pressure of existing compressor on site.

Wellbore Scenarios Where Unit Works

Figure 1 – Kick Around Unit Figure 2 – Kick Around Unit Cylinder Manifold

Manpower

Figure 4 – Kick Around Unit At Fill Station

Figure 3 – Unit Hooked Up To Kick Down Casing

Canadian Natural currently has an alliance with Flo Solutions who initially participated in the design and development of the technology. The Flo Solution staff own and operate the Kickaround units exclusively. Canadian Natural operators will tie the Kickaround unit into the gas well and circulate gas to dewater the well. As the Kickaround unit is a flat bed truck with the gas bottles on the back, it only requires one operator.

Additional Uses

The Kickaround unit is also capable of assisting in pipeline maintenance. Canadian Natural has used the unit to clean fluid from gas pipelines of fluid. A pig is placed in the pipeline and the Kickaround unit is hooked up to push the pig down the line. As many of the gas pipelines operate at low pressure and are connected to low pressure gas wells, the time it takes to pig a line without the Kickaround unit, often exceeds 3-5 hrs. Conversely, on suspended gas lines, no producing gas wells may be available making it impossible to pig the line without an external pressure source. By utilizing the Kickaround unit, Canadian Natural has reduced the time it takes to clean a low pressure gas line as well as clean out lines which previously were unable to be cleaned out. This has had a positive impact our Canadian Natural’s pipeline integrity program. Further it has reduced Canadian Natural’s operating costs by reducing labour costs.

Chemical treating of gas wells is another use for the Kickaround unit. Occasionally, some gas wells will develop a buildup of heavy tar-like material called asphaltenes. This build up can occur at the sandface of the wellbore perforations, which in turn impedes the gas production. Canadian Natural is using the Kickaround unit to help treat these wells with chemical or condensate. The procedure involves circulating the chemical or condensate down the wellbore and spotting it near the well perforations. The Kickaround unit is then hooked up to the well and using the high pressure gas, the chemical or condensate is squeezed into the formation with the intention of breaking down the asphaltene buildup. By performing the chemical squeeze using the Kickaround unit, Canadian Natural is able to enhance production at a reduced cost compared to standard chemical squeezes.

Summary

The evolution of the Kickaround unit has made a significant impact in how Canadian Natural has optimized, restarted, dewatered and stimulated low pressure gas wells. The innovative thinking by the field staff at Canadian Natural has helped lower operating costs while maintaining production forecasts.