Underbalanced Coiled Tubing Drilled Horizontal Well in the North Sea
- Philip Wodka (Maersk Olie Og Gas AS) | Henrik Tirsgaard (Maersk Olie Og Gas AS) | C.J. Adamsen (Maersk Olie Og Gas AS) | A.P. Damgaard (Maersk Olie Og Gas AS)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- May 1996
- Document Type
- Journal Paper
- 406 - 413
- 1996. Society of Petroleum Engineers
- 1.7 Pressure Management, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 4.1.2 Separation and Treating, 2 Well Completion, 4.1.5 Processing Equipment, 2.4.3 Sand/Solids Control, 3.1.6 Gas Lift, 1.7.7 Cuttings Transport, 3 Production and Well Operations, 5.8.7 Carbonate Reservoir, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 4.3.4 Scale, 4.5 Offshore Facilities and Subsea Systems, 3.3.2 Borehole Imaging and Wellbore Seismic, 1.6.6 Directional Drilling, 1.6 Drilling Operations, 1.11 Drilling Fluids and Materials, 1.1.3 Trajectory design, 1.10 Drilling Equipment, 1.14 Casing and Cementing, 6.5.2 Water use, produced water discharge and disposal, 1.6.1 Drilling Operation Management, 5.6.4 Drillstem/Well Testing, 1.7.5 Well Control, 1.12.2 Logging While Drilling, 1.7.1 Underbalanced Drilling, 2.2.2 Perforating, 1.5 Drill Bits, 3.3.1 Production Logging, 5.1.2 Faults and Fracture Characterisation, 1.6.7 Geosteering / Reservoir Navigation, 4.3.1 Hydrates
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Maersk Olie Og Gas AS has drilled a 3,309 ft long near horizontal drainhole with coiled tubing to a total measured depth of 11,000 ft in the Danish sector of the North Sea. The well was completed in May 1994 as a 3 1/2" open hole producer in the Gorm field chalk reservoir
Part of the well was drilled at underbalanced conditions with oil production rates of up to 1,100 stb/d during drilling. Conventional well test equipment was used for handling returns. A nearby process facilities platform supplied liftgas and received the produced hydrocarbons during the drilling phase.
Worth noting are the penetration of several chert layers, the fairly long reach, and the application of geo-steering Indications are that the well productivity is significantly improved compared to that of a conventionally drilled well, but problems were experienced with borehole stability in a fractured region.
Maersk Olie og Gas AS (Maersk Oil) produce approximately 180,000 stb/d of oil from soft chalk reservoirs in the Danish sector of the North Sea. The largest producing fields have reached a stage, where the majority of the development activities concentrate on infill drilling and implementation of secondary recovery by means of water injection. Since 1989, development activities have almost exclusively been based on horizontal wells with a total of 78 wells drilled in five fields. Most of these wells are completed with a 7" cemented liner and perforated in multiple intervals with each interval straddled by 4 1/2" tubing (PSI system) for stimulation and production management purposes (Ref. 1 and 2).
As part of the continued efforts to produce the reservoirs in a cost effective manner and increase ultimate recovery, the emerging technology of coiled tubing drilling is seen as one possible method of obtaining low cost well re-entries, e.g for sidetracking and well extensions. It is recognized that the attractiveness of this technique depends on the long term production performance, including borehole stability, and the capability to decrease the costs, e.g. by performing the drilling operation from existing wellhead platforms on the relatively small wellhead platforms in the Danish sector, limited deck space necessitating placement of equipment on two bridge connected wellhead platforms and limited crane lifting capacity are the main problems in this respect
No field proven method had been developed for sidetracking from a horizontal well with a coiled tubing drilling assembly. Therefore, surface tests were initiated onshore in a coiled tubing test loop during August 1993. The objective was to test the technical feasibility of performing sidetracks and well extensions from existing horizontal 4 1/2" PSI completions with 3.688" restrictions. Several methods were tested, and a successful horizontal through tubing sidetrack was achieved already in the second attempt.
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