Predicting and Preventing Wellbore Instability: Tullich Field Development, North Sea
- Kenneth A. Russell (Schlumberger) | Cosan Ayan (Schlumberger) | Nick Hart (Kerr-McGee North Sea UK Ltd) | Jean Rodriguez (Kerr-McGee North Sea UK Ltd) | Howard Scholey (Kerr-McGee North Sea UK Ltd) | Christopher E. Sugden (Kerr-McGee Oil & Gas Corp.) | John K. Davidson (Predrill Stresses Intl.)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- March 2006
- Document Type
- Journal Paper
- 12 - 22
- 2006. Society of Petroleum Engineers
- 1.11 Drilling Fluids and Materials, 1.6.9 Coring, Fishing, 5.1.7 Seismic Processing and Interpretation, 1.6.7 Geosteering / Reservoir Navigation, 3.3.2 Borehole Imaging and Wellbore Seismic, 1.6.2 Technical Limit Drilling, 2 Well Completion, 1.6.1 Drilling Operation Management, 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties), 5.6.4 Drillstem/Well Testing, 5.6.1 Open hole/cased hole log analysis, 1.6.6 Directional Drilling, 5.3.4 Integration of geomechanics in models, 1.2.1 Wellbore integrity, 1.2.2 Geomechanics, 5.1.2 Faults and Fracture Characterisation, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 4.1.5 Processing Equipment, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 3.3 Well & Reservoir Surveillance and Monitoring, 3.3.1 Production Logging, 3 Production and Well Operations, 2.4.3 Sand/Solids Control, 1.6 Drilling Operations, 1.1 Well Planning, 1.12.2 Logging While Drilling, 5.1.5 Geologic Modeling
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Innovative geomechanical, drilling, logging, and seismic techniques have been used to successfully develop a geologically complex discovery in the North Sea, Tullich field. With individual reservoir-unit thicknesses below the limit of seismic resolution, and a restricted depth window for completion, optimal placement of horizontal production wells was vital to the successful and economical development of the field. Wellbore instability was a key concern after recent experiences while drilling similar formations in nearby fields. These events had resulted in significant nonproductive time and cost overruns. A geomechanical model was constructed from data acquired during the appraisal-drilling phase and was used to make stability predictions for the proposed horizontal production wells. Wellbore instability while drilling was prevented through the application of a real-time wellbore-stability management system that validated the stability predictions by monitoring surface and downhole drilling parameters, produced solids, fluids, and log data. By combining efficient teamwork and a variety of logging and drilling technologies, the complex reservoir was successfully developed, both in terms of cost savings during well construction and subsequent oil production that exceeded expectation.
The Tullich oil field is situated in Block 9/23a (Fig. 1) and operated 100% by Kerr-McGee North Sea (U.K.) Ltd. It lies 5 km south of the Gryphon field and came on stream in August 2002 as a subsea tieback from a central manifold to the Gryphon "A?? floating production, storage, and offloading facility.
Hamilton Brothers originally discovered the field in 1991 by drilling Wells 9/23a-27 and 9/23a-27Z, where thin oil- and gas-bearing sands were encountered within the Eocene Balder formation. The sidetrack Well 9/23a-27Z was successfully drillstem tested. However, development of the prospect was not considered commercially viable at the time. Advances in seismic and drilling technologies led Kerr-McGee to reconsider the prospect and acquire the block in 1999. In 2001 they implemented an exploration and appraisal program by drilling two vertical Wells (9/23a-29A and 9/23a-31) and six sidetracks (9/23a-29Z through 9/23a-29U).
Kerr-McGee recorded a 3D seismic survey in 1990, and in 1999 a 3D ocean-bottom cable (OBC) seismic survey was acquired over the Gryphon field and northern part of Block 9/23a. Inversion of the shear data from the OBC survey indicated the potential for extensive development of the Lower Eocene Balder sand, culminating in the exploration drilling program in 2001.
The reservoir is of excellent quality and is interpreted to be a complex of turbidite sands, which lie in the Balder B2 zone directly above the massive tuff (Balder B1 zone) shown in Fig. 2. While the individual sands are below seismic resolution, the package could be mapped on the new seismic. An oil column extends 200 ft between a gas cap above and an aquifer below.
The development program of four horizontal wells began in early 2002 with the drilling of Well 9/23a-T2 and concluded in October the same year with the completion of Well 9/23a-T3. The wells had horizontal sections between 3,852 and 5,606 ft.
This paper describes how the seismic, core, drilling, and logging data acquired during the appraisal phase were used to evaluate wellbore-stability hazards, and how that information was included in the successful drilling and completion of the horizontal development wells. Details of how drilling and well-placement difficulties in this structurally complex environment were overcome are presented in recent publications by Greiss et al. (2003) and McDonald and Tribe (2003).
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