Planning for success

Optimum completion. Photo from Weatherford.

Weatherford’s Yvonne McAnally and Ben Lake show how collaboration and integrated methodology delivered an operator’s first subsea well project in Norway.

The risky business of oil and gas development is no more evident than in the subsea sector, where the complexities of positioning the wellhead and infrastructure on the sea floor have taken technology development to a new level of sophistication.

In venturing into this important frontier, however, the industry has learned that successful completions require more than the application of advanced tools and technologies. Operators are looking for methods that bring integration and collaboration to the subsea arena, from extensive planning and testing, to the installation of correct equipment to ensure wells are designed and produce as expected.

In 2013, a North Sea operator used an integrated, collaborative approach to complete its first subsea well project in Norway. This was a two-year undertaking that resulted in two satellite oil wells being successfully brought online. For service company Weatherford, the project was the first fully integrated subsea completion involving both the upper and lower sections of a subsea well.

The wells, at total vertical depth of 3600m (11,811ft), are located in the North Sea’s Jette field, estimated to hold 14MMbo. The region is highly regulated by Norway’s Petroleum Safety Authority (PSA), which oversees technical and operational safety in hydrocarbon production, ensuring that companies implement the appropriate safety barriers to ensure long-term well integrity. Weatherford was selected to design, build and install the subsea completion into 9 5/8-in. main-bore casing strings for the two subsea wells in 127m (417ft) of water. The wells were eventually tied back to the ExxonMobil-operated Jotun B production platform.

The completion system needed to include a safety valve, packers, liner hangers, swellable packers and screens, as well as the capability for the required cable and gas-lift systems and well control. The cornerstone of the operation was Weatheford’s Optimum cased-hole upper-completion system, which combines various modular tools that, when used together, create a customized solution based on the needs of a specific well.

Weatherford worked closely with the operator in conducting extensive analysis of the reservoir data to ensure selection of the proper equipment. Extensive studies of the expected production profiles and planned operating life of the wells were performed, along with casing configurations, connections and subsurface tree design, which has an impact on how the completion is carried out. For example, trees must be designed to enable operations, such as chemical injection, that may be required later in the production life of the well.

Well on paper

The planning phase included a comprehensive well design on paper, where both companies examined the running procedures for every aspect of the completion, including all the equipment that would be needed for the lifespan of the well. The process was repeated several times prior to equipment installation. Ongoing project management also included a quality control plan that documented the quality-assurance requirements for the safe manufacture, inspection and testing of all cased-hole completion components for the wells. Most of the equipment was built in Houston or Aberdeen to meet the delivery deadline.

Since many wells in the region at some point require artificial gas lift to enhance recovery, the design incorporated gas lift mandrels and other equipment to eliminate the need for future costly workover operations. Risk and contingency planning also were built into the completion design.

The lower completions included more than 100 standalone screens with inflow control devices (ICD) that were installed to regulate flow into the screens and establish consistent production. The ICDs also prevent formation sand from creating localized erosion, a phenomenon known as hot spots. Swellable packers were installed in the open hole zone to isolate the formation’s different production zones and prevent cross-flow between the zones in the event of a pressure differential. Liner packer hangers were installed to take the weight of the tubing string and serve as barriers between the reservoir and the casing.

For the upper completion, all elements of the Optimum completion platform were implemented. The OptiMax tubing-retrievable, surface-controlled subsurface safety valve (SSV) was installed to provide positive shutoff protection in the event of a catastrophic well control incident. SSVs are required in the Norwegian North Sea for well control and to prevent the release of any reservoir fluids. Safety was further enhanced by a 9 5/8-by-5 ½-in. hydrostatic set removable production packer that provided a seal between the outside of the production tubing and the inside of the casing.

Avoiding workovers

Because most North Sea wells are completed with chemical lines in the event chemical injection is required during the lifespan of the well, a chemical injection mandrel with shear-out valve was installed to deliver production chemicals, such as scale and paraffin inhibitors. By installing the lines at the outset of the project, the operator can avoid a subsequent costly well intervention operation.

The same rationale applied to the pre-installation of two 5 ½-in. gas-lift mandrels, both unloading and orifice styles, for artificial-lift, an operation that simulations conducted during the planning phase had predicted could be needed within 12-18 months after the wells were brought online to maintain production rates.

After the upper completion was run, a 10 ¾ in.-by-5 ½-in. tubing hanger was run and landed in the hole. Pressure tests were conducted on the tubing hanger. The production packer was set and final pressure tests were carried out on the production tubing, packer and the chemical injection control line. The installation procedure was completed with an inflow test of the SSV and other pressure tests on the tubing hanger and valves set in various positions.

The customized completion system was successfully installed in both wellbores, with the entire operation finished two days ahead of schedule, reducing rig time and associated costs. In the lower completion, the standalone screens and ICD protected the sand from hot-spotting. By providing an effective seal between the outside of the production tubing and the inside of the casing in the upper completion, the hydrostatic set removable production packer eliminated the need for additional wireline work, resulting in further cost savings. Pre-installation of gas-lift mandrels and the chemical-injection system will eliminate the need for future workovers to maintain production.

The two wells were brought online 2Q 2013, and are currently producing 14,000 b/d. The success of the collaborative strategy encouraged the operator to implement the approach for additional wells in the region. The Optimum completion system has since been updated to include a radio-frequency identification (RFID) module that uses radio transmitters and receivers to control packer setting and opening/closing of sleeves, which further reduces costs and enhances safety.

As operators continue to exploit complex and risky subsea well projects, collaborative, integrated methods that include extensive planning, strong project management and innovative application of advanced technologies are critical to maximizing production while enhancing safety.

Yvonne McAnally serves as global product line director, upper completion for Weatherford. Over the last 16 years, she has held various roles in engineering, marketing and business development. She has a BS in mechanical engineering from University of Houston. 

Ben Lake serves as the global product line director, safety systems, for Weatherford.  Over the last 12 years, he has held various roles in engineering and marketing.  He has a BS in mechanical engineering and a MBA from Oklahoma State University.