Critical Technologies for Success in Extended Reach Drilling
- M.L. Payne (Arco British Ltd.) | D.A. Cocking (BP Exploration) | A.J. Hatch (Anadrill/Schlumberger)
- Document ID
- Society of Petroleum Engineers
- SPE Annual Technical Conference and Exhibition, 25-28 September, New Orleans, Louisiana
- Publication Date
- Document Type
- Conference Paper
- 1994. Society of Petroleum Engineers
- 2.2.2 Perforating, 1.6.10 Running and Setting Casing, 1.14 Casing and Cementing, 2.4.3 Sand/Solids Control, 1.12.1 Measurement While Drilling, 1.10 Drilling Equipment, 1.2.5 Drilling vibration management, 1.6.3 Drilling Optimisation, 1.6.6 Directional Drilling, 1.1 Well Planning, 1.6.2 Technical Limit Drilling, 4.1.5 Processing Equipment, 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties), 1.11 Drilling Fluids and Materials, 1.6.1 Drilling Operation Management, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 1.2.2 Drilling Optimisation, 1.11.4 Solids Control, 1.4.1 BHA Design, 1.6 Drilling Operations, 1.12.3 Mud logging / Surface Measurements, 1.4 Drillstring Design, 1.12.2 Logging While Drilling, 1.7 Pressure Management, 1.2.3 Rock properties
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This paper overviews critical technologies for extended-reach drilling (ERD). ERD is a pivotal industry activity because it enables optimisation of field development through the reduction of drilling sites and structures and provides access to otherwise unavailable reserves. These efficiencies increase profit margins on viable projects and can make marginal prospects financially viable.
ERD technologies to be reviewed include torque/drag, drillstring design, wellbore stability, hole cleaning, casing considerations, directional drilling optimisation, drilling dynamics, and rig sizing. These technologies have been found critical to the success of ERD.
Overview of the Wytch Farm ERD Project
BP Exploration owns majority interest and operates the Wytch Farm (WF) oilfield on behalf of its partners ARCO British Ltd., Premier Consolidated Oilfields, Clyde Petroleum, Purbeck Exploration, and Goal Petroleum. The WF field was discovered in 1974 and is located southwest of London on the UK coastline near Poole, England. The main producing reservoir in the field is the Sherwood Triassic Sandstone which contains about 270 million barrels of recoverable oil at 1585m TVD. About a third of the Sherwood's reserves are offshore under Poole Bay. Previous plans to develop the offshore reservoir with an artificial island were cancelled in favour of ERD from an onshore drillsite as depicted in Figure 1. This action, taken in 1991, followed various ERD achievements in the industry which made the feasibility of ERD at WF more evident.
By avoiding the artificial island, ERD development of the offshore Sherwood reservoir is expected to save $150 million in development costs and has accelerated the production of offshore oil by 3 years. Table 1 shows well data for the WF ERD project in terms of wells drilled and now being drilled, The second well, F19, is believed to have set a world record for reach at the subject reservoir depths. That record is being broken by F21, the well currently being drilled and will be furthered by later wells now being planned. Figure 2 shows how WF wells compare to other published ERD operations. Wells have been provisionally scheduled with reaches of 6.2km and studies are ongoing on 7km well designs and drilling/completion procedures.
Figure 3 shows a generic ERD well schematic for WF. 26" conductors are preset on the drillsites. The 18.5/8" casing is set in 24" hole at 220m TVD to protect surface aquifers. The 17.1/2" hole is drilled to 750m TVD to the base of the reactive Oxford Clay. Shale inhibition in this section is achieved with KCl additions to the water-based mud (WBM). Following setting of 13.3/8", cementing to surface, and installation of BOPs, WEM is displaced to low-toxicity mineral oil based mud (OBM). A 12.1/4" hole is drilled to finish the build to the high tangent angle which is then held for the long 12.1/4" sections. These 12.1/4" sections are up to 4500m long at over 800 inclination. The top of the Sherwood is identified and then 9.5/8" casing is run and cemented. The 12.1/4" mud weight of 1.25 sg used for wellbore stability is reduced to 0.98 sg in the 8.1/2" section as the reservoir is mechanically competent and losses into the depleted production sand need to be minimised. The 8.1/2" reservoir section is built from the tangent angle to near-horizontal. Reservoir is drilled until sufficient productive interval has been exposed and the well is then dropped off through the oil-water-contact. A 5.1/2" liner is run and cemented across the reservoir. The wells are perforated underbalanced and completed with large ESP completions utilising 5.1/2" tubing. Production rates vary from 14,000 to 20,000 BOPD in the ERD wells. Prior to the ERD project, WF was producing 68,000 BOPD. Current field production with three (3) ERD wells on stream is now over 90,000 BOPD.
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