Advances in the Completion of 8km Extended Reach ESP Wells
Authors: Jariwala H. , Davies J. , Hepburn Y. 
Published: December 2007

This paper describes the key planning and operational experiences gained during the completion phases of the record breaking extended reach wells at the Wytch Farm oil field in England. Nine wells have been drilled, of which four have a horizontal departure in excess of 6 kilometres. Well 1M-O5SP (M5) currently holds the world record for the highest departure well, 8,035m, at any vertical depth, and a record departure:true vertical depth (TVD) ratio of 5.0.

The Wytch Farm extended reach wells are completed with cemented, perforated liners and electrical submersible pumps (ESPs). This paper presents an overview of how the wells have been completed and describes how a combination of existing technology and new technology has been applied to meet the challenges of designing and completing very long reach wells. The paper includes a detailed discussion of open hole data acquisition and perforation of reservoir sections in excess of 2,000m in length. Running ESP completions and packer setting in horizontal sections is also discussed, together with experience of using a 'formation saver valve' device. The paper reports experience gained, identifies improvements made and reviews lessons learned from well to well. In particular, there is a discussion of a number of ESP failures observed from the use of very long electrical cable and a variety of wellhead penetrator systems, and how these were overcome.

It is hoped that the conclusions will be of use to other projects contemplating the completion of extended reach wells with cemented, perforated liners and also the completion of ESP wells in general, where high power ESPs and/or long cable lengths are involved, e.g., subsea completions.

Introduction

The Wytch Farm development is located in an unusually sensitive environmental area on the south coast of England. The main Sherwood sandstone reservoir lies under Poole Harbour, and extends offshore under Poole Bay (Figure 1). Nearly one half, (ca. 145 million barrels), of the Sherwood's 330 million barrel reserves, lies in the offshore extension.

The Sherwood is a Triassic sandstone, with top reservoir at Ca. 1,585m TVD subsea with a maximum 110m column of oil bearing sand above the oil water contact (OWC).

During 1991, advances in drilling technology enabled offshore recovery to be contemplated using extended reach wells drilled from existing onshore facilities (Reference 1).

Since project sanction in December 1991, 9 extended reach wells have been drilled and completed within the initial well programme. Well productivity and drilled lengths have far exceeded initial expectations and led to many records being set for drilling and completion performance. Details of well departure and completion statistics are given in Table 1 together with operating statistics.

Well Completion Overview

This section summarises the completion design and completion operations. Key aspects of interest in four areas, namely open hole data acquisition, perforating, completion running and ESP experiences are then detailed in subsequent sections.

Well Design. The shallow reservoir depth requires that the tangent angle of the well trajectory (Figure 2) is built very quickly from the top of the 12-1/4" hole section. A tangent angle of 70-85 is maintained from this point to top reservoir. The tangent section is cased off with 9-5/8" casing. The reservoir section is then completed with a 5-1/2" liner in 8-1/2" hole, cemented and perforated with 3-3/8" guns.

Reservoir section profiles and perforating strategy have been modified during the well programme as shown in Figure 3. In the early wells, hole angle was built from the tangent section to near 900 to maximise productivity from the high permeability sands in the Lower Sherwood, with the tail angle of the well dropped to penetrate the OWC for regional mapping purposes.

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