Multilateral drilling technology has been used in many heavy- oil developmental projects to achieve maximum reservoir exposure from a single surface location. The wellbore geometry and completion strategies for multilateral wells are planned and customized to fit the known reservoir characteristics and sand distribution qualities. Typically, heavy oil reserves are found in unconsolidated sandstone reservoirs that require some form of sand exclusion strategy across the reservoir as well as at the lateral mainbore junction interface. In heavy-oil sand, effective sand-control strategies must be carefully planned since one of the difficult problems to address in heavy-oil targets is their natural tendency to suspend formation solids, often referred to as Basic Solids and Water (BS&W) solids. An effective sand control strategy should allow these solids to be produced to surface and separated by the production facility. The remainder of the solids can be controlled, based on the sand-distribution qualities. If the formation sand is uniform, liner-only completions can be used for effective sand exclusion without sacrificing rate. If the formation sand is non-uniform, gravel packing will be required. For this reason, regardless of the well scenario, the gravel pack or liner only completion should allow BS&W solids to pass through and be produced to the surface.
Most heavy oil development areas use artificial lift such as PCP and ESP pumps. All multilateral completion strategies must always consider the lift strategy, the ID requirements for pump deployment as well as necessary sand exclusion requirements for the pump.
The paper examines successful multilateral completion strategies used in heavy-oil development projects in Canada, Trinidad and Venezuela. It will also explore new synergistic technologies that will impact future development strategies.
Multilateral well-construction technology continues to gain global acceptance as an economically viable and effective heavy oil field development strategy. Heavy crude oils, which are typically identified as having API gravities of <20 degrees and viscosities of >1000 centipoise, represent an estimated 5.5 trillion barrels of global reserves. These heavy oils are traditionally found in weak, unconsolidated sandstone reservoirs that require some form of lateral borehole support and/or sand control solution. Another key to successful heavy oil exploitation is reservoir exposure which increases the mobility of high viscosity liquids within the reservoir matrix. Proven reservoir exposure techniques such as horizontal drilling and well completion technologies have been further enhanced through the successful integration of these technologies into multilateral well construction strategies1.
Lateral access must always be a primary consideration when planning the completion type and junction requirements for any heavy-oil development. If lateral access might be required during the life of the well, there are several re-entry techniques that can be deployed with the primary completion system as well as with remedial strategies. Lateral sand control methods have ranged from perforated and/or slotted liners to horizontal gravel-pack methodologies. In-zone junction placements usually require a sealed junction, which minimizes and/or eliminates formation sand production. If the junction placement is in a competent shale section above the reservoir target, a non-sealed junction may suffice.
While the primary objective of multilateral well construction is reservoir exposure, an optimal lateral design must be chosen for the completion also and integrated into the overall well construction strategy. The lateral completion requirements must consider two issues. The first issue is effective reservoir-completion interface, which must also be considered in conventional, single heavy-oil wells.
Traditional heavy-oil horizontal completion methods range from openhole perforated liners to horizontal gravel packing. The extent of lateral sand control or borehole support requirements will vary and depend on issues such as reservoir lithology, oil viscosity, BS&W solids content along with the solids-handling capacity of the surface facility.