Abstract

The redevelopment of West Delta Block 89 consisted of two re-entry wells completed as 6¾ in (172 mm) openhole gravel packs with 4 in (102 mm) pre-packed screens inside 500 ft (152 m) horizontal holes. These two wells were the first application of horizontal technology for Agip Petroleum in the Gulf of Mexico and more than doubled oil production at West Delta 89, while being under planned time and budgets.

This paper will demonstrate that with open communication during the planning and execution phases between operating personnel, service companies, and contract personnel, advanced technology can be employed successfully on the first attempt. Overcoming challenges such as complex directional profiles to ensure proper placement of horizontal wells in a thin oil column between a gas cap and water aquifer, high torque and drag, formation damage, hole cleaning, and completing relatively slim holes requiring sand control are discussed. An industry milestone was achieved on the second well when a steerable rotary assembly was used to kick off the directional well in a soft formation for the first time.

The results are summarized for the wells A-9 and A-21, and expand the use of re-entry drilling technology in complex directional trajectories, and openhole horizontal gravel packing (OHGP) in relatively slim holes. Applications exist in fields requiring an alternative to cased hole gravel packing and in field redevelopment projects where perceived marginal economics exist.

Introduction

Economic redevelopment of an offshore field demands a cost-effective solution that maximizes production. Generally, the field is in some stage of water breakthrough and the oil column is relatively thin. Therefore, horizontal re-entry drilling is an effective option, provided that the drilling of the horizontal section is maintained in the oil column. However, in unconsolidated formations, sand control is required and typically is difficult when small casing to screen annuli exist, which is common in re-entry wells. Openhole horizontal gravel packing (OHGP) is an effective way to achieve maximum production while providing sand control in such wells.

Agip Petroleum's West Delta 89 redevelopment objective was to place horizontal laterals in a thin oil column in the lower "P" sand, then complete the wells with an OHGP. A complex directional profile was needed to properly position the lateral in the reservoir. Due to an overlying gas cap and an underlying water leg in the reservoir, effectively completing the wells posed several challenges.

Wells A-9 and A-21 were successfully drilled and completed under budget, with minimal trouble time. The A-9 lateral was positioned on the western side of the field, with the A-21 lateral placed on the eastern side of the field as shown in figure 1. The resulting oil production from both wells was water free and without any "free" associated gas. Project economics for pay out and rate of return were easily met.

Background

The West Delta 89 field is located in the Gulf of Mexico approximately 200 miles southeast of New Orleans, Louisiana in 210 ft (64 m) of water. The field was discovered in 1988 and resulted in the setting of a 28 slot, 8 pile platform. Twenty-four wells were drilled prior to production start up in March 1991. Agip Petroleum assumed operatorship in December 1991. There are 18 producing wells, 2 water source wells, and 4 water injectors.

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