Solid Expandable Tubular Technology: Case Histories of Value-Adding and Enabling Applications in Sabah Deepwater Campaign

Abstract

Solid expandable tubular technology has seen an impressive uptake in recent years. The technology has the potential to reduce cost, increase production and give access to new reserves. In 2004/2005, Shell Malaysia Exploration & Production installed solid expandables in seven wells, putting itself at the forefront of the technology and adding significant value to the business. The design philosophy that has been adopted in Shell Malaysia can be described as:Use solid expandables as a planned-in contingency application in case the "trouble zone or event" is encountered. This approach allows for planning of aggressive well designs that fall back to expandables to mitigate problems.Use solid expandables in base-case casing design for deepwater wells with more than 5,000 to 6,000 ft below mud line and with four casing string design. This paper describes four case histories of solid expandable tubular technology for the Sabah Deepwater exploration campaign in Malaysia. The technology was successfully applied and was very instrumental in achieving the well objectives and delivering a successful exploration campaign. The key to this success was strong management support throughout the process. This took the form of creating an enabling environment to taking on board new technology and also by supporting actions to build up solid expandable tubular stock in the region to be able to quickly react to opportunities. Technology support in Malaysia was provided through representation of Shell's Global Implementation Team for solid expandables, making sure that global lessons were shared and best practices were applied. The Global Implementation Team also worked closely together with the technology provider on QA/QC and job planning aspects, which helped to keep a 100% success record with solid expandables tubulars for Shell in Malaysia. Introduction In 2004, Shell and its partners started an exploration campaign in Sabah Deepwater, offshore NW Borneo, Malaysia. Figure 1 indicates the location of the block. Shell Malaysia acted as the operator of the block on behalf of the partnership. Drilling took place in water depths ranging from 1,931 to 4,831 ft. The Sabah Deepwater area is characterized by elongated NE-SW toe thrusts that parallel the NW Borneo Trough and shelf edge. The age of these thrusts is from middle/late to recent Miocene. Turbidite sediments have been deposited from mid-Miocene to the present and are both unconfined and confined in character and controlled by the timing of the thrust structures. The limited accommodation space along the narrow shelf caused eroded sands from the mountainous hinterland regions of Sabah and the inboard area to cascade over the shelf edge into the toe-of-slope and basin floor through a system of upper slope feeder channels and canyons. The onset of toe thrusting becomes younger outward and pre-deformation turbidite sands are unconfined sheets in a toe-of-slope depositional environment leading to a clastic sequence of rapidly stacked reservoirs. Basin modelling indicated that the toe-thrust structures within the Sabah Deepwater trapped hydrocarbons migrating from a mature source kitchen in the deep basinal trough. The trapped formation pressure, with the addition of basin inflationary overpressure trends from background aquifer overpressures within the individual reservoir units, yielded a pore-pressure prediction with possible steep changes in overpressures with formation depth. These geological characteristics and the overlying water depth posed three major drilling challenges:Weak formation strengths in the shallow sections as a result of the reduced overburden stressSharp predictions of pore-pressure transition in the stacked reservoirsNarrow drilling margin from the formation strengths and predicted formation pressures with the increasing probability of losses and well control problems during drilling