Since the first patents related to multilateral technology were filed in 1929, drilling and evaluation technology has advanced at a rapid pace, enabling multilateral drilling to become a common method of cost-effectively developing reserves around the world.

Various types of multilateral projects exist, and each project has its own specific challenges. Reservoirs that benefit most from multilateral drilling as a field development strategy to increase drainage area per well include low-permeability tight reservoirs and heavy oil and thin reservoirs, coalbed methane resource developments, shale gas basins, and reservoirs prone to coning undesired fluids.

To increase production, reduce costs, delay coning, and minimize the environmental impact, a whole-asset-team approach is necessary in planning and executing these operations. To determine the most effective means to develop a field, a complete understanding of the reservoir and well-construction process is required. A global network of subject matter experts who are able to connect directly with local operations, such as certified drilling and completion application engineers and geoscientists, is needed.

Multilateral development

Baker Hughes’ applications engineers use proprietary software to design extended-reach drilling (ERD) solutions for drillstring design, torque, and drag modeling and hydraulics management in the wellbore, enabling the operator to make better decisions. In one of the world’s most complex and extensive multilateral field developments, the Statoil Troll field, Baker Hughes worked closely with Statoil to develop specific technologies and operational procedures to drill and recover oil. At the time of discovery Troll was considered a gas field that contained a considerable amount of oil. However, due to accessibility challenges in the reservoir’s thin oil column, oil production from Troll was considered technically unfeasible.

Today, through the extensive use of precisely positioned multilateral wells, Troll has become Norway’s largest oil field and has delivered more than 1 Bbbl of oil. By combining multilateral drilling with ERD, enormous amounts of a reservoir can be exposed from a single slot using up to seven laterals.

Critical data for ERD

Advanced correction and quality-control techniques for MWD surveys that use multiple sensors and continuous measurement can reduce uncertainty while drilling, particularly true vertical depth, which is critical in ERD wells. LWD services include images of geological features provided by high-definition LWD imaging tools and deep-reading acoustic shear tools in tandem with a geochemistry and magnetic resonance system.

Personnel work closely with the operator’s team to place the well in the optimum stratigraphic position within the reservoir to maximize both initial production and ultimate recovery. The company’s Reservoir Navigation Service (RNS) reduces stimulation costs and potentially decreases the number of wells required to effectively drain a reservoir.

Additionally, the RNS can help operating companies drill and complete difficult horizontal wells and multilaterals with improved penetration rates and decreased hole tortuosity as a result of significant reductions in unnecessary course corrections.

Surface systems use communications algorithms to pull the signal from the most complex noise environments as a method for meeting the demand for more data while drilling. Baker Hughes developed a high-speed telemetry service, which is tiered and linked to the requirements of each well.

Increased ROP and reduced surface rotary speed decrease the number of drillstring rotations per foot of hole drilled, which lowers drillstring and casing wear in multilateral drilling operations.

Coiled tubing for ERD

Drilling multilaterals with coiled tubing in reentry well applications can prove challenging due to the increased flexibility of the coiled tubing (CT) compared to conventional jointed pipe, which can hinder steering control as well as the effectiveness of openhole sidetracking operations. However, a directional drilling bottomhole assembly can contain automated closed-loop steering functionality with downlinking from the surface to precisely steer slim-hole reentry wells.

The limited-reach capability of standard bottom-hole assembly (BHA) setups in CT drilling applications is extended with the use of rib-steered motor technology. Straight and/or optimized wellbore trajectories are now possible with the lowest required dogleg severity and minimized tortuosity.

A reduction in the friction of the CT string with the borehole wall is achieved, resulting in a smoother weight transfer to the BHA and a deeper CT depth measurement in the wellbore profile.

An electric hydraulic orienter allows the tilt of the drilling motor to be oriented in the desired direction, allowing CT drilling to be a cost-effective drilling method for ERD.

Liner hanger systems

Liner hanger systems are an important enabling technology for both extended-reach and multilateral wells. In extended-reach applications liner hangers are used to secure long liner strings from intermediate casing to total depth. A float-in liner assembly meets the challenges associated with running a liner in extended-reach horizontal wells where significant hole drag can result in the need to run multiple liner strings. The float-in liner string can decrease the weight of the liner by filling it with air. This reduces the friction between the liner and the borehole wall and allows use of longer strings. A specially designed landing sub in the float-in running tool string enables the drillpipe to be filled with mud for weight and rigidity while the liner stays full of air.

Liner hanger technology also helps enable completion of multilateral wells in problem formations. On a recent well in Ecuador, the operator wanted to drill and complete a multilateral well from a tight surface location through a potentially collapsing limestone formation below 3,636 m (12,000 ft). Baker Hughes combined its EZ-Case liner drilling technology, an expandable liner hanger, and the Hook Hanger multilateral junction to ream the liner to 3,662 m (12,015 ft) and continued drilling another 41 m (134 ft). The Hook Hanger provided support for the lateral casing string. The 7-in. by 9 -in. expandable liner hanger was hung off, and the running tool was released before displacing cement or setting the packer.