Abstract

ML technology was started in PDO since 1994 where over 240 ML have been drilled in PDO majority of them are level 2. The increasing complexity of well architecture demands more complex ML systems. Many system available in the market are not mature yet and the other do not meet the specific requirement of PDO. As it is known the main drives for this technology is a reduction in UTC by combining wells (One surface casing, one X-mass tree, and one completion) and reduce number of locations hence surface facilities as the pipe lines and headers. PDO activities with ML can be divided into three different applications. Northern fields where there is no hole instability or sand production problem therefore level 2 is of great success. As an example, in Saih Rawl wells the 6 to 8 producing laterals of level 2 from the same backbone is a routine construction. However, in the southern carbonate fields the hole instability and sand production problems exist. To avoid the sand production problem the lateral should be lined up by WWS or PDL, which required level 3 junction. The present of highly unstable shale at the cap rock add more complicity to the system by requiring a high strength junction for ML system. The third application of the ML technology is in deep stringer oil wells and gas wells where a level 6 system could be applied in the future where high pressure is required due to the reservoir high pressure. This article will brief in the experience we have with different ML systems of level 3 and how this drive us for the level 4 MX-select from Smith Red Baron which is initial design to meet our requirement in Amin field. Also this article will show how to go through sand production and shale ingress through the junction where a cemented junction is not appropriated (Flanged Hook Hanger) and the learning points from the first trial.

Deep set ML design

The Amin Field located in Southern Oman with the reserves contained in a single sandstone reservoir at depth of 900 m. Due to the highly unconsolidated sand, the Wire Wrapped Screens are very essential for the completion design. The Original design of Amin ML consists of a 9 5/8" surface casing and 7" cemented liner (Figure 1). The 9-5/8" casing are run and cemented in the Shammer Shale at ±750m. The 8 1/2" hole is then landed horizontally in the reservoir. Both legs completed with 4 1/2" WWS one drilled along the 7" shoe and the second leg out of the window in the 7" liner. The liner in the second leg was extended all the way to the 7" motherbore with perforated joints to allow the production from the fist leg to flow through it. It was absolutely necessary to be able to measure the production from each leg and to prevent sand production through the window. This lead to the introduction of the External casing Packer (ECP) in the second leg and deployed just outside the window. The inflation of the ECP was not successful in many cases, due to the damage of the packer element when passing over the window. The possibility of ECP failure in the second leg lead to the sand production around the window. Sand production leads to choking of the flow path for leg 1 and cause great damage to the ESP. Moving the window from the reservoir to the cap rock solve this problem. This lead to the introduction of the Deep set design (Fig 2) where the surface casing was run all the way to the cap rock. Both laterals penetrate the cap rock shale allowing for much higher separation between the reservoir entry points. Shale closing in on the sand control liner in the second leg provided isolation between the two laterals.

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