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Analysis

Slotted Liner Applications for Production Optimization

Tue, 01/22/2013 - 14:33

Designed primarily for sand control, but with several other uses, slotted liner is a fairly well established and low cost oil and gas technology for open-hole well completion. It serves as an alternative to pre-holed or pre-drilled liner, where sand flowing into the well can often cause production difficulties. There are two main alternative sand control technologies currently being used by operators around the world: gravel packs and sand screens. However, as John Bilsland, Director General of Regent Energy Group Mexico explains, “on one hand, the gravel pack is often a less exact solution when it comes to sand control. On the other hand, sand screens are effective, but the cost of placing them in long sections of horizontal pipe is often prohibitive.”

In some ways, slotted liner works in a very similar way to gravel pack solutions: a natural barrier is created that stops sand from flowing into the well. Regent Energy Group produces a liner for this purpose that has very fine slots - ranging in thickness from that of a sheet of paper to around 6 millimetres and with an approximate length of 4 centimetres - depending on data received from the customer regarding the formation they are drilling in and the granule size of the sand in the formation where the liner is to be inserted.

The slots are cut longitudinally in the pipe, and as oil flows through the slot, it carries sand with it. This sand is stopped in the slot, where it forms a natural bridge, and acts as a filter for fine sediment, which results in cleaner oil flowing into the liner. “Slotted liner provides you with a better grade of oil, as well as fewer processes at the surface to get rid of the sand, and the resulting crude is a lot easier on your surface equipment because you are not bringing up abrasive sand with your oil,” Bilsland asserts. This works best when the slots in the liner are seamed: after slots have been cut in the pipe, they are transversally rolled at a given pressure, which forces the top of the slot to close slightly, forming a slot with V-shaped sides, with the wide end of the V facing into the liner. As sand comes into this slot, it stops at the top, where the gap is narrower. This shape is also intended to make blockages in the slots much less likely to occur: the V-shape means that the built up blockage can easily flow out of the slot.

Bilsland explains that there are additional applications for slotted liner. As well as being used for sand control, the liners can also be utilized for steam injection, a key tool in producing heavy oil. Vacuum insulated tubing allows operators to maintain a high steam temperature all the way down into the well and to the slotted liner, where it is then distributed throughout the well via the slots. “Often, if steam has not been run through vacuum insulated tubing, it has turned to water by the time it gets to the end of a horizontal well. Hot water injection does have some value, but it is nothing compared to applying steam,” says Bilsland. Regent also has tools to ensure that distribution of steam is constant throughout the well, rather than having poor distribution of steam towards the toe of the well.

Another application for slotted liner, currently being tested in a pilot project, is water injection in marine environments. “Slotted liner allows for water injection throughout the formation, while being able to manage the pressure of the water being injected,” Bilsland details. The company is also investigating applications for slotted liner in coalbed methane and shale gas production.

Whilst slotted liner has been used for some years in countries like Canada, Colombia and Venezuela, its introduction in Mexico is a fairly recent event. Because Pemex is now tackling the challenge of heavy oil in fields like Samaria, steam injection is being used increasingly, and slotted liner is increasingly being applied to the NOC’s heavy oil extraction projects. Pemex also has to deal with sand control issues at some wells, according to Bilsland, which means that the potential demand for the company’s liner is growing. Regent Energy is also finding work with private sector service providers and integrated service contract winners.

Another area where the company has seen some early success in Mexico is working with Pemex on well recompletions. A pilot test at a well that was recompleted with Regent technology has seen great production improvements, and according to Bilsland, Pemex was extremely happy with the results. It seems that, given the multiple applications for slotted liner and the NOC’s receptiveness to it, this technology is destined to gain increasingly widespread acceptance in the coming years.