Steerable Drilling Liner (SDL) was originally designed to remove downtime related to drilling in unstable formations and/or into depleted formations as it allows the well to be lined/cased off simultaneously as it is drilled. The SDL system consists of a standard drill pipe as the inner-string, inside a conventional liner. The system uses a conventional rotary steerable Bottom Hole Assembly and has been designed to drill complex 3D well trajectories, up to 2000 m long, with the same directional and logging capabilities as conventional drilling. Two sizes are developed: 7" for 8 ½" hole and 9 5/8" for 12 ¼" hole. Using SDL gives several benefits to the drilling process, including: Reduced openhole time; the liner is always on bottom. Reduced pressure fluctuations; tripping of BHA/innerstring is always in cased hole. Reduced mechanical impact on the formation; stable centralised liner with no lateral movement against formations when drilling. All the above will contribute greatly in the goal of preventing formation collapse prior to drilling a section to planned total depth (TD). Based on a request from the Grane field in the Norwegian Continental Shelf (NCS), additional ways of using the SDL technology has now been introduced as an 7" SDL system was drilled fully into open hole and left as an open hole clad (with both the liner top and bottom in a reservoir sand) to prevent unstable intermediate formations to collapse and subsequently prevent drilling the 8 ½" reservoir section to planned TD. Unstable shale protruding into the reservoir at Grane causes regular adjustment to the wellpath. As the formation instability develops over time, getting the liner/completion through a shale interval has been proven difficult and often results in sidetracks due to wellbore collapse and/or pack-offs. The solution has been to place the well path above the shale intrusions to avoid the stability problems. This drilling practice limits the total reservoir drainage since the gravity based drainage only allows the reservoir above the drilled wellpath to be produced. Using 7" Steerable Drilling Liner (SDL) on a well on the Grane platform allowed drilling through the shale section and seal it off immediately before problems started to develop. This enabled optimisation of the well placement for improved access to reserves that otherwise would be inaccessible due to shale intrusions. The entire operation was carried out withd great success. SDL not only removed drilling related issues but also contributed to, based on the more optimally placed wellpath, increased reserves. At TD, the liner was released from the inner-string without any issues and left as a horizontal protection through the shale with both ends of the liner in the reservoir sand.

Using Steerable Drilling Liner to drill through an unstable formation has been a proven solution from fixed installations where this technology greatly increases the chance of successfully drilling a wellbore and landing a liner at planned depth. The key to the increased performance are the reduced open hole time, mechanical impact on formation and pressure fluctuation in the well. In previous subsea wells on the Vigdis field on the Norwegian Continental Shelf, stability problems have led to setting the liner prematurely, resulting in loss of production. The stability problems seen in the offset wells have been time dependant, with few difficulties experienced during drilling. However, when running the liner afterwards, pack-offs, shallow setting of liners and problems with cementing have occurred. The Steerable Drilling Liner solution was selected to prevent initiation of instability while drilling the reservoir and in addition to ensure the section could be secured with the liner in place before formation instability problems occur. The implementation of the Steerable Drilling Liner enabled drilling of a nearly horizontal section with several unstable palaeosol intervals without any stability related problems, hence meeting the objective of reaching a challenging target. It has been concluded that the section would have been difficult to drill with conventional methods. In contrast to previous Steerable Drilling Liner utilization, this well was drilled from a semi-submersible rig in rough weather conditions. These harsh conditions in the North Sea demanded high attention with respect to drilling practices and well control which had to be addressed accordingly. In the following, the planning and execution phase, leading up to the successful drilling operation from a floating installation will be described. The paper will also touch upon some improvements for further use of the Steerable Drilling Liner technology.

The Steerable Drilling Liner is an integrated drilling system that combines the advantages of rotary steerable drilling- and logging-technology with the liner drilling concept. This allows drilling complex 3D wellpaths with the same logging and directional capabilities as a conventional drill string, enabling operators to drill and secure the wellbore with a liner in one continuous operation. The technology has been successfully applied in several drilling operations and has been recognized as a method to overcome stability challenges in unstable formations. The technology offers the following benefits compared to conventional drilling: Reduced initiation of formation instability due to: – Reduced hydraulic surge (no tripping in open hole) – LBHA/drill-string always tripped in cased hole also when a bit trip is required – Reduced mechanical load on borehole wall – Low rotational speed (~30 rpm) and fully centralized liner with "non-rotating" centralizers prevent mechanical interaction between pipe and borehole wall. – Low shock and vibration effects due to low rotation speed reduce risk of tool failures Reduced time consumption and open hole time: – Remove time between drilling and lining of formation. Wellbore secured before collapse processes start – Reduced operational time as reaming, back-reaming, wiper trip or general wellbore conditioning are not required for successful liner installation This paper will elaborate on the Operators Steerable Drilling Liner technology experiences. Focus will be on the mechanisms why Steerable Drilling Liner is an enabling technology when used in unstable/troublesome formations, compared to conventional drilling methods. It will also describe expected future utilization and applications and finally touch upon the next generation SDL system, which currently is under development.

In liner drilling operations the annular velocity of the drilling fluid drops significantly when it transits from the narrow cross section of the openhole-liner annulus into the increased annular volume between the casing and the drillpipe above the liner. The reduced annular velocity might cause critical hole-cleaning problems that can jeopardize the entire drilling operation and therefore needs to be managed. To effectively mitigate this problem Statoil (operator) and Baker Hughes (service company) have jointly developed and tested a smart flow diverter (FLD) that can be positioned in the drillstring directly above the liner running tool. The FLD is designed as a standalone tool that can be placed anywhere in the drillstring and can be used in different applications where enhanced hole cleaning is required, independently of the measurement-while-drilling (MWD) supplier. The tool ultimately must deliver a continuous flow split during the drilling operation, so the main considerations of required features and specifications were carefully reviewed in the early phase of the project:• Unlimited activation/de-activation on demand • Failsafe closed • No compromising of and interference with normal well-control procedures • Direction of flow exit to annulus • Adjustable flow split • No interference with mud pulse telemetry

In liner drilling operations, the annular velocity of the drilling fluid drops significantly when it transits from the narrow cross section of the openhole-liner annulus into the increased annular volume between the casing and the drillpipe. The reduced annular velocity above the liner can cause critical hole cleaning problems that can jeopardize the entire drilling operation and, therefore, must be managed. To effectively mitigate this problem, a major operator and service company jointly developed and tested a smart flow diverter that can be positioned in the drillstring directly above the liner running tool. The flow diverter (FLD) is designed as a standalone tool that can be placed anywhere in the drillstring and is independent of the measurement-while-drilling (MWD) service-supplier. It can be used in different applications, e.g. under-reaming operations and liners without tieback, where enhanced, continuous hole cleaning is required. The fluid bypass of the flow diverter is simply activated either by drillstring rotation and flow or by a flow pattern signal if string rotation is not possible. These surface manipulations are recognized and interpreted by the flow diverter sensors and electronics. The concept enables an unlimited amount of activations and both activation principles can be incorporated into standard connection procedures, thereby eliminating nonproductive time (NPT). The FLD went through extensive testing and was run in steerable drilling liner and in other applications. The paper presents the features and activation principle of the technology, its benefits and field experience in combination with steerable drilling liner (SDL) technology and how the utilization of the technology in an underreamer application resulted in an optimized bottomhole assembly (BHA) design preventing previously experienced formation washouts.