Optimal Configurations of Multiple-Lateral Horizontal Wells
Authors: Retnanto A. , Frick T.P. , Brand C.W. , Economides M.J. 
Published: December 2007

Drilling multiple-lateral wells and employing intelligent completion systems would very likely lead to considerably higher productivity and increased recovery at relatively low incremental costs. Completing such a well system is a challenge and today it is still considered an extravagant effort. An important reason is that the performance of wells with multiple-lateral completions has not yet been investigated fully.

There are several potential configurations for multiple-lateral wells, including planar, multi-planar, branches etc. The reservoir geometry and especially the areal and vertical-to-horizontal permeability anisotropies are critical. Using a versatile simulation model, the calculation of the multiple-lateral well performance is presented. Based on example calculations, optimum spacing, length and number of sidetracks are identified for various reservoir conditions. Shape factors for a number of well configurations are presented.

Introduction

Multiple-lateral well systems have become a compelling recent topic in the petroleum industry. The reason is that these wells can provide several interesting, and previously inaccessible, opportunities to drain a reservoir efficiently. The idea of spanning a bundle of drainholes out of a single hole and connecting these drainholes with the surface is an appealing possibility. Similarly, drilling one or more horizontal sidetracks from an existing vertical wellbore is a means to enhance the production of the well. Although costly to drill and fraught with operational challenges, these wells may provide better economics than stimulating a specific horizontal well or drilling new wells.

Obviously, any decision to drill (multi-) laterals should be based on careful evaluation of the expected well system performance, operational and economic risks, possible production scenarios and, very importantly, (selective) wellbore management and maintenance of the individual drainholes. The technology to drill lateral well branches (often short radius and often using coiled tubing) is available today. However, selection of the right candidates and production and completion technologies is critical. Thus, several new developments and improvements of existing concepts can be expected in this area. This paper highlights reservoir engineering and production aspects of multiple- lateral well systems. Uncomplicated methods for calculating inflow performance of various well configurations are presented and important production engineering concepts are discussed.

Classification of Multiple-Lateral Well Systems

Multiple-lateral systems are wells with more than one lateral leg branching into the formation(s). This general definition gives rise to several configurations listed below and pictured in Fig. 1:–Multi-branched wells (Fig. 1a)–Fork wells (Fig. 1b)–Several laterals branching into one horizontal "mother hole" (Fig. 1c)–Several laterals branching into one vertical mother hole (Fig. 1d)–Dual opposing laterals (Fig. 1e)–Stacked laterals (Fig. 1f)

Selection of the most beneficial well system for a given reservoir is the challenge. The available systems can be and have been classified according to drilling (curvature, workover vs. coiled tubing rig, conventional vs. slimhole), completion (cased and perforated or slotted liner vs. open hole), production, and reservoir engineering aspects. This paper will be limited to the reservoir and production engineering aspects.

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