Unique ESP Completion and Perforation Method Maximizes Production in World Record Step-Out Well

Abstract

Summary In this article we describe the key planning and operational experiences gained during the perforation and completion phases of the world record step-out extended reach well at the Wytch Farm oilfield in Dorset, England. We present an overview of how the M-11 well was completed successfully and describe how a combination of existing and new technology was applied to achieve Wytch Farm's most prolific producer. Well 1M-11SPy (M-11) the world record for the highest horizontal departure, 10 114 m, at any vertical depth, and a record departure to true vertical depth ratio of 6.24. The Wytch Farm extended reach wells are completed with cemented, perforated liners and electrical submersible pumps (ESP's). A new technique for perforating the well was developed to maximize inflow efficiency. This technique enables underbalance perforating without any subsequent requirement for a well kill. The impact of these improvements on completion efficiency is discussed, along with associated operational issues. The large departure required the ESP to be set at 8625 m, another world record, with the 1,000 HP motor requiring a new 7 kV cable system and a 1500 kVA variable speed controller (VSC) at the surface. We describe the VSC selection and the physical testing of the complete ESP/cable/VSC system, which was conducted before installation to ensure that sufficient torque could be generated at the ESP for a range of startup and operating conditions and to configure the new type of VSC used for optimal system performance. We also report the experience gained and review the lessons learned. Introduction The Wytch Farm development is located in an unusually sensitive environmental area on the southern coast of England. The main Sherwood sandstone reservoir lies under Poole Harbour and extends offshore under Poole Bay (Fig. 1). The Sherwood is a Triassic sandstone with the reservoir top at 1585 m true vertical depth (TVD) subsea with a maximum 110 m column of oil-bearing sand above the oil/water contact. Approximately 90% of the field total reserve basis is contained within the Sherwood reservoir. Nearly one half of the Sherwood's 430 million barrel reserves lies in the offshore extension. During 1991, advances in drilling technology enabled offshore recovery to be considered as the preferred option, utilizing extended reach wells drilled from existing offshore facilities. Since the start of extended reach drilling (ERD) in 1993, 15 ERD wells have been drilled with stepouts ranging from 3800 m up to the record breaking result of 10 114 m for well M-11. The geoscience planning, drilling, and completion of Wytch Farm ERD wells have been extensively documented. The field is now in a mature development stage and was producing approximately 100 thousand BOPD. Background Drilling Summary. Figs. 2 and 3 show the final well trajectory. A 9 5/8 in. casing was set just above the Sherwood reservoir top, which allowed 8 1/2 in. drilling of the reservoir. After drilling approximately an 800 m horizontal section into the reservoir, it was apparent that the wellbore was high within the structure, and had insufficient permeability thickness (kh) to achieve the well objectives (M-11z). At this point, it was decided to abandon this wellbore and perform an openhole sidetrack (M-11y). The sidetrack was completed successfully in the openhole section just below the 9 5/8 in. casing shoe and wellbore and drilled to its record-setting horizontal departure and total depth. The hole was then lined and cemented. Well Performance. Prolific productivity indices (PI's) for the project, up to 135 B/D/psi, have been achieved, of which M-11 realized a PI of 45 B/D/psi. As discussed in detail later, these high productivities, coupled with relatively low reservoir pressures, have pushed ESP technology to the technical limits in terms of capacity and power requirements. In addition, the inability to effectively interpret pressure-transient test data has resulted in uncertainty in determining precise completion efficiency and PI potential estimates. Perforating and Workover Operational Histories. The conventional tubing conveyed perforating (TCP) underbalanced shoot, kill pill, and test string recovery method has previously been adopted as the preferred completion technique. Key issues of the deployment technique, charge design criteria for debris, and kill pill formula were engineered to minimize formation damage and maximize productivity. In addition, workover operations have traditionally relied on pumping viscous, fibrous lost circulation material (LCM) kill pills that were perceived to be nondamaging to attain well control. Current production logging tool (PLT) information has indicated that select production intervals are not contributing to production. There is no obvious reason for this selective productivity other than that the intervals may be plugged with residual LCM. Because of the operational complexity and associated high costs to attain PLT data, baseline data are not readily available to distinguish between formation damage from the initial perforating vs. subsequent workover operations. With production depletion and known decreases to static reservoir pressure, the recent risk of kill pill formation damage has increased because of greater applied overbalances in combination with less available production underbalance. ESP and Drive Summary. The three different types of VSC's that Wytch Farm uses to control ESP systems are a variable voltage source quasisquare wave, a current source, and a constant voltage source pulse width modulated (PWM).

Inflow Performance Relationship for Perforated Horizontal Wells

“…in some fields, horizontal wells may need to be cased and perforated. Selective perforating have been implemented in the horizontal wells drilled in many fields such as Bongkot, 1 Joanne, 2 Andrew, 3 Oseberg, [4][5] Wytch Farm, 6 Statfjord, 7 Elk Hills, 8 Beryl, 9 Dan, 10 Alba, 11 Yowlumne, 12 and Prudhoe Bay. 13 In the Bongkot Field, the deviated wells were perforated across multiple reservoirs and equipped with sliding sleeves to allow selective production.…”

“…gun with 6 spf at the poorer quality sands. 6 Production logs have indicated that some of the perforated intervals are not contributing to production.…”