Multilateral Techniques Enhance Feasibility for Deepwater Applications with Limited Reserves
Authors: Longbottom Jim R. 
Published: October 2008

Abstract
In deepwater development, operators must address unique reservoir management conditions that traditionally increase surface facility, completion, and well maintenance costs. To effect economic feasibility for deepwater development, therefore, operators have been compelled to target only reservoirs that promise the greatest production from each well as candidates. Multilateral completion techniques have now beenintroduced that offer solutions to the problems of the high costs inherent to deepwater development. These new completion systems offer design concepts that have the capability to 1) mechanically connect lateral liners to a parent casing, 2) allow through-tubing re-entry access to selected laterals, and 3) provide isolation from adjoining zones at the junctions of the laterals and parent wellbore.-what makes these advantages particularly appealing for deepwater development is the fact that the production potential can be increased without an increase in sea floor facility requirements. The systems can offer more productivity per well slot, reduce the number of slots required, reduce total drilling footage and associated costs, and reduce template or platform sizes and weights, all factors that control well economics. Additionally, reservoirs previously considered as marginal can be economically developed. This paper will review case histories of drilling, completion, and well servicing with a particular emphasis on recent experiences gleaned from a floating rig application. This will illustrate the applicability of multilateral technology to deeper water field development. In addition, the capability to remotely monitor and control laterals will be discussed with a case history review of where this technology has been applied. The flexibility of this type of completion and the associated benefit of providing production options from alternative zones has been shown to reduce the risks previously associated with costly deepwater developments because of the increase in production potential provided by multiple zones. The systems have demonstrated technical feasibility, and although only recently introduced to deepwater needs, economic feasibility that allows development of marginal reserves offshore.

Background Of Technological Advancements
Although multilateral well concepts date back to the early 1900's, this technology has just recently become more feasible for field developments.1,2,3,4 New techniques allow lateral wellbores to be cased with the lateral liner being connected back to the main wellbore casing, and isolation of the junction to be achieved with cement or through mechanical means. In addition, the lateral liner size is maximized in relation to the main wellbore casing to retain the flexibility of access through the lateral with conventional drilling and completion tools. These multilateral completion schemes have been used in several fixed platform applications and have now also been implemented in a floating rig application. Examples of development scenarios, the type of multilateral applicable, and how economics are enhanced are detailed below.

Economics
Multilateral wells have the potential to increase recoverable reserves in a given asset in addition to decreasing the overall drilling and completion costs. The following scenarios are examples where multilateral well solutions are applicable. I. The well system shown in Fig. 1 involves a platform for which justification was based on a known and prolific reservoir.