Abstract

The installation of the first single-trip Technology Advancement for Multilaterals (TAML) Level 4 multilateral (ML) junction system was completed in a subsea, gas-injection well. It was drilled to support oil production from the Tilje and Ile formations in the Smørbukk Sør field in the Norwegian Sea, approximately 193 km offshore in 300 m water depth.

After injecting for ten years, the well will be converted to a gas producer from the same formations. Because of the Norwegian Sea's environment, the multilateral system had to be low risk and simple to install, with the capacity to minimize pipe trips and withstand the heaving seas. The casing exit had to be long enough to accommodate running a rotary steerable system through the window to drill the lateral to TD. This window had to be milled in a single trip in 13%Cr 110 casing followed by milling into the Garn 4 hard-impermeable sandstone with possible quartz stringers.

Hollow-whipstock technology has been employed for more than ten years in the North Sea, but a new system, designed to be installed in a single trip--a savings of two pipe trips--was selected for this project. The hollow whipstock was perforated through after the liner was installed in the lateral to regain hydraulic access to the main bore below the junction. The hollow whipstock was used for the milling and production/injection phases and was not retrieved, saving an additional pipe trip. The well completion used several cementing and completion products and services, including liners with screens and swell packers. Stage cementing was performed to isolate permeable formations between the junction and the reservoir.

The well was successfully completed and gas injection began with increases in production being noted from the adjacent producing wells. Although it was unusual to use a multilateral well for gas injection, the technology proved that it can be applicable to any multilateral well requiring a Level 4 junction.

Introduction

The Åsgard license is a subsea development incorporating three separate fields, Smørbukk, Smørbukk Sør and Midgard. It is located approximately 193 km offshore Norway in some 300 m of water depth in the Norwegian Sea where largely unpredictable and extreme weather conditions are the norm (see Fig. 1). Winds can change from dead calm to full gale in a period of less than one hour and the accompanying sea conditions present major challenges to both equipment and personnel. The prospect development is well advanced and available slots in the subsea templates for new well development are at a premium.

As a result, new wells are more cost effective if a multilateral approach is used that enables the maximization of drainage points in the reservoirs. On the Smørbukk Sør field there are four templates, three for production wells and one for injection which had only one available slot (the R-3). Studies of injection patterns and requirements concluded that additional injection was required into both the Ile and Tilje formations to optimize production patterns. Another complication was the fact that both zones would require sand-control installations. A multilateral well was then planned with the objectives of providing the needed gas injection and allowing for subsequent conversion to a gas producer after ten years in operation.

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