In heavy oilfield development, optimal flow rates usually directly correlate to reservoir exposure. In the case of heavy-oil development, reservoir exposure will play an even greater role because of the inherent flow-resistant characteristics of this type of hydrocarbon. For this reason, heavy oil completions have not been exploited fully. However, by implementing horizontal drilling and the state-of-the-art completion methods now available, heavy oil fields are now being revitalized.
By employing multilateral technology (MLT), the benefits of horizontal drilling and state-of-the-art completion practices can be magnified still further. A drastic increase in the reservoir exposure from a single surface location can be strategically placed within the reservoir using multiple horizontal laterals. This development strategy reduces the number of surface locations and facilities, subsequently decreasing the overall field development costs. The added benefits are accelerated production and enhanced oil recovery, which increase the net present value of the asset.
In multilateral implementation, the reservoir characteristics will always dictate the lateral window placement relative to the reservoir body along with the type of lateral interface with the parent bore. There are various types of lateral interfaces with the parent bore, which have been classified by the Technology Advancement of Multi-Lateral (TAML) Organization.
This paper will review various heavy-oil multilateral applications and will include window construction and the integration of lateral completion strategies such as openhole liners and gravel-pack applications. It will also focus on other multilateral issues such as lateral accessibility and isolation techniques, remedial options, and guidelines for selecting a "fit-for-purpose" lateral window system.
Introduction
Economical development strategies are essential in heavy oil exploitation around the world. Maximum reservoir contact is paramount in heavy oil developments because of the viscosity of heavy oil. Furthermore, heavy-oil lifting and refining expenses mandate greater single-well-flow rates to enhance the economic viability of the asset. Through the implementation of multilateral techniques, reservoir drainage can be increased at a relatively low incremental cost when compared to conventional well construction.1
Different types of multilateral wells have been deployed in heavy oil development (Fig. 1), and splayed or fishbone designs are among the most common multilateral drainage strategies used. Under this construction scenario, multiple laterals or branches, which typically are positioned horizontally across the reservoir, extend from a single mainbore casing. During planning, proper reservoir engineering should consider the degree of reservoir communication required as well as the length of each individual lateral or branch.2
Traditionally, heavy oil reserves are found in unconsolidated sandstone reservoirs, which may require some form of formation sand exclusion and/or borehole stability device. This can range from slotted or perforated liners to premium screens or can require horizontal gravel-pack completions. Sand or solids exclusion and control may also be required at the junction where lateral and mainbore interface. Lateral junctions placed in the producing zone will almost always need some form of sand exclusion system at the lateral and mainbore interface.
The objective of complex reservoir drainage architecture is to increase the reservoir exposure, and thereby, increase potential flow rates and hydrocarbon recovery. Commingled production from multiple laterals is very common in heavy oil reservoirs, and this completion scenario simplifies the multilateral completion requirements and flow configuration.
In heavy-oil scenarios, optimal production rates are achieved using artificial-lift techniques such as progressive cavity pumps (PCP) and electric submersible pump (ESP) production systems.3 Lateral access or re-entry should be considered as part of the completion and artificial lift strategy and can be accomplished with or without pulling the production tubing and pump.
