In Shell Exploration & Production, swelling elastomers have been deployed in a variety of applications: as a means to establish zonal isolation in liner completions, as a production separation packer, and as an integral part of an expandable open hole clad. In these applications, the elastomers have been run in various open hole, casing, and tubing sizes. A total of around 60 deployments in Shell have been recorded, all of which were technically successful. Case examples of each of the three mentioned applications will be presented from Shell operations in the North Sea, the Middle East, and the Far East. Introduction In most areas where Shell operates, especially in the more mature oil field environments, there is a high focus on well cost reduction. Various technology applications have been identified to meet this business need and allow the operator to drill wells cheaper and smarter, making the most of existing infrastructure. One technology that is experiencing a rapid uptake is the application of swelling elastomer packers. These packers, which swell naturally when exposed to the appropriate swelling agent, have successfully been used as a replacement for traditional mechanical packers and cement. The business case for using swelling elastomer packers is different per application and can include time savings as well as direct tool cost savings. Shell implemented swelling elastomers in combination with the deployment of a Solid Expandable Tubular (SET) system called Open Hole Clad (OHC) in July 2002. First application of swelling packers for zonal isolation was in the South Furious field in Malaysia in June 2003. Since then, over 60 deployments have taken place in operations in Malaysia, Brunei, Nigeria, Gabon, Oman and the UK. Theory and Definitions A swelling elastomer packer, or swelling packer, is a rubber element vulcanised onto pipe. The main property of the rubber is that it swells significantly when exposed to either aromatic hydrocarbons or saline water through a process of absorption. An oil swellable packer is a swelling elastomer packer, which swells primarily through the absorption of hydrocarbons. This is a diffusion process. Typical operating temperatures for oil swellables are 80–130°C. A water swellable packer is a swelling elastomer packer, which swells through the absorption of (saline) water. This is an osmosis process. Typical operating temperatures for water swellables are 50–90°C. The three main design parameters of swelling packers are life-span, pressure rating, and swelling time. Because of the relatively recent development of swelling packers, our understanding of these parameters is still growing and a full theoretical treatment of the subject is beyond the scope of this paper. The main factors to consider in determining the three design parameters are temperature and the geometry of the pipe, packer and borehole. Pressure ratings have been tested up to 3500 psi, although higher ratings have been recorded in the industry. Swelling times in our operations range widely from 5 to 50 days. The case examples provided in this paper show three distinctly different uses of the swelling elastomer packer: the liner completion, the production isolation packer, and the expandable open hole clad. A liner completion is defined as a liner system with slots or perforations to allow access to the producing formation. The swelling packers are used in combination with blank liner joints to isolate oil bearing zones from water zones, where conventionally a cement column would be used. The production isolation packer is defined as a seal between a production tubing and a production liner in order to isolate the various perforated sections. Swelling packers are used to replace conventional hydraulically or mechanically set packers. An expandable open hole clad is defined as an expandable tubular used to seal off water bearing formations or water producing fractures in a barefoot well section. Swelling elastomers are used to provide the seal between formation and tubular.
Shell Exploration & Production in Aberdeen, Scotland has implemented through tubing rotary drilling (TTRD) as a cost effective method of accessing small accumulations of hydrocarbons in some of its mature assets in the UK sector of the North Sea. Working together with its contractors, the implementation of TTRD has taken place over the past 6 years. The most recent experience is a 5 well campaign on the North Cormorant platform during the past year. This paper gives an overview of the implementation process including a history of the work done, highlights and lowlights of drilling operations that have taken place to date. However, it focuses on the issues that were addressed in relation to the current campaign. Topics that will be covered are: Planning Process: An evaluation was done leading up to the current campaign to identify the areas of improvement that would yield the highest value. Resources were dedicated to the improvement initiative, beyond what would normally be assigned for conventional drilling operations. Novel Drilling Fluid Application: The conventional weighting agent (barite) was replaced by manganese tetra-oxide to give a low rheology fluid with enhanced anti-sag characteristics. Drilling Performance Optimisation: Work was done to reduce the torque requirement of the drill bits used for TTRD and match those requirements to the capability of the slim hole drilling motors for the required hole size. Equipment Upgrades: Surface equipment and downhole tools were developed and existing tools improved in order to improve performance and increase overall capability. Critical equipment that was either developed or significantly improved included: kick detection equipment, directional drilling bottom hole assembly, perforating guns, and swelling elastomer packers. The benefit of TTRD, demonstrated by the successful campaign on the North Cormorant, is being carried forward to the rest of the Shell Exploration & Production organisation through the establishment of Global Implementation Team specifically for through tubing drilling. Shell is looking forward to realizing the benefit of this technology worldwide. Introduction1 The North Cormorant Field was discovered in 1975 and brought onto production in 1982. The field is located 120 miles (190 km) north-east of the Shetland Islands in the northern North Sea. Production from the field peaked at just over 20,000bbls oil/day in the mid 1980s and then dropped slowly to its current level of below 5,000bbls oil/day. Throughout the life of the field, there have been over 100 wells drilled. One of the main sections of the reservoir is characterized by a high degree of faulting and poor connectivity. The faulting combined with the requirement for water injection makes production from this part of the reservoir difficult to achieve. The combination of the following factors:Large number of penetrationsFaulted and isolated nature of the reservoirSmall size of the individual fault blocks has led to a situation with:A reasonable understanding of the stratigraphyLarge numbers of wells required to access the remaining reservesSmall remaining accumulations. All of the above highlighted the need for a drilling technique that would make it possible to drill low cost, short sidetracks without the requirement for a full Logging While Drilling (LWD) capability.
In 2011, a deepest horizontal Coalbed Methane (CBM) well in China, with a total vertical depth in excess of 1100m, was successfully drilled by Shell China E&P Co. Ltd (SCEPCo). The well, located in the East Ordos Basin, achieved a total 'in-seam' length of nearly 3600 m. The integration of technology across multiple disciplines, which enabled this well to be a success, is presented in this paper. An integrated geological evaluation of both regional and block scale data was used to map the depth, continuity, thickness and gas content of the coal seams. This evaluation, together with understanding of structure and distribution of faults, was then used to pick a well location in an area where the coal seams are thick and the gas content is high. The uncertainties in the evaluation are greater where the coal seam is deeper and include factors such as the stress field, coal mechanical properties, structural complexity of the seam, presence of a roof aquifer and the permeability. When planning the drilling of the well, a comprehensive drilling strategy, together with sidetrack and drilling fluid programs were prepared prior to the campaign. This preparation was invaluable for successfully drilling the first horizontal well despite the geological uncertainties present. The MWD technology and expertise in geosteering were also essential to successfully drill the horizontal laterals in this area as there is a potential aquifer in the limestone roof which needs to be avoided and there are kink bands in the coal seams. A geomechanical evaluation was also completed to understand the stress field and the orientation of fractures in the coal seam. This is required to understand and balance the trade-off between orienting the horizontal laterals to maximize production against maintaining the stability of the well bore. After completion of the well, the well production was initially affected by several shut-ins which delayed gas production. A combined dewatering and control system was then adopted which was shown to effectively mitigate fluid level buildup issues arising from unexpected workovers and well shut-ins. In conclusion, this well demonstrated the feasibility of drilling horizontal CBM wells in the area deeper than 1100 m and it is expected that this technology can be applied in the near future to unlock the potential of other deep CBM opportunities in China.
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