Abstract

This paper describes how the team at Wytch Farm met the challenge of drilling and completing selective re-entry laterals in an increasingly price competitive and performance-focused environment. One of the key elements in this success was the creative application and modification of existing technology. Utilizing predominantly mature technology, the team was able to proceed with confidence in the management of risk associated with new applications.

Introduction

The Wytch Farm Field is the largest onshore oilfield in the United Kingdom. The producing formation extends under Poole Harbor, a recreational area and wildlife sanctuary. As such, the area is highly sensitive from an environmental perspective. Hence, work in the field must be performed under strict conditions while remaining cost competitive. In this instance, combining mature technologies enabled both requirements to be met.

First, the paper explains how a selective re-entry system works. Second, it describes the functionality of a one-trip milling system. The paper then describes how the wellbore scenario enabled these technologies to be combined, providing additional benefits without additional risk. Finally, the paper describes the successful utilization of the system to create two multilateral wells at Wytch Farm.

Selective Re-Entry System

Selective re-entry systems have been in use for several years. The system components include a big bore packer with an orientation key, a mechanical latch, extensions (as required), a debris sub, an alignment device, and a casing exit system.

Historical utilization of the system began with setting the big bore packer below the lowest lateral to be drilled. Next, survey tools were used to determine the orientation of the key inside the packer. Based on the orientation of the key, the alignment device was manipulated and placed below the whipstock to ensure that the window was created in the proper direction. A debris sub was installed to prevent a potential malfunction caused by the cuttings from the milling operation. Depending on the desired results, extensions were added between the alignment device and the whipstock to space out the exit from the packer. The mechanical latch was added below the extensions. Thus, the assembly consisting of the mechanical latch, extensions, debris sub, alignment device and whipstock were run in the hole and secured to the big bore packer.

In its normal application, the selective re-entry system included a conventional two or three trip casing exit system. This meant that the aforementioned whipstock assembly was typically run in hole on the starter mill. Once the assembly was securely latched into the packer, the starter mill was sheared free of the whipstock. At that time, an initial cut out was created. The next trip consisted of a window mill and watermelon mill. If necessary, a third trip could be added to further elongate the window. Finally, the appropriate drilling assembly was run to create the lateral.

Upon completion of the lateral, the whipstock assembly was retrieved using a hook or a die collar. This meant the anchor latch, debris sub, alignment device and any extensions were all retrieved simultaneously. All that remained in the well was the big bore packer, through which, the original borehole could be accessed, albeit at a reduced diameter.

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