Screening Variables for Multilateral Technology

Abstract

Introduction The multilateral well was one of the leading technologies of 1999, and it will continue to be one of the leading technologies for the next 5–10 years. It is likely that because of the cost reduction driver, management will ask, "Why isn't this a multilateral well?" much like the current justification for horizontal wells. The two challenges in 2000–01, unmet in 1999, will be consistent success of the technology and the low cost multilateral. When evaluating multilateral technology, it is important to understand three things. First, in its simplistic scenario, the only difference between a multilateral well and a sidetrack or redrill is that the original wellbore will remain open when placed on production. The second thing to note is that multilateral technology is a reservoir development technology rather than a drilling technology. The drilling department is simply the vehicle by which this reservoir technology is brought to fruition. And third, all major operating companies will utilize multilateral technology; the question of consequence is ‘when?’. The purpose of this paper is to present the first steps in applying multilateral technology to the operator in a practical way. This paper will cover only one aspect of multilateral technology - screening variables. These screening variables should be viewed as fundamental criteria from which, to begin a multilateral feasibility study. One of the screening variables is the driver for multilateral technology. Since the business driver must be evaluated before any other screening variable, it will be covered first. The remaining variables will be covered according to the order in which they appear in the planning, design, and implementation of a multilateral project. The completion variables will be specified first, followed by reservoir and geological screening variables. Finally, drilling and other general screening variables will be covered. Discussion of the different classifications or levels of multilaterals is taken from the TAML (Technical Advancement of Multilaterals) Classification system (Chambers1, Mackenzie and Hogg2). Business Drivers for Multilateral Technology While the following list of business drivers for multilateral technology is not complete, it represents the primary justification for considering the technology application. All multilateral projects will have a combination of drivers specific to the field application. Cost Reduction This business driver is almost always considered in conjunction with one or more drivers. The purpose of the technology is to reduce CAPEX. The concept of multilateral technology is to incur only the additional cost of rig time, tools, services, and equipment needed to drill and complete an average deviated lateral of 300-1500 feet. The costs of mobilization/ demobilization, casing, and drilling to top of zone will essentially be borne by the main wellbore. A typical cost reduction model would have the multilateral well contributing up to twice the production, but only 1.5 times the cost of a monobore completion. Similarly, a trilateral may cost twice the monobore completion, but supply up to three times the production. Increased Reserves Additional reserves may be isolated lenses of pay or compartmentalized reservoirs. The degree of the compartmentalization will dictate the number of laterals and the wellbore geometry needed to optimally exploit the reservoir. Multilateral technology may also allow access to smaller or marginal reservoirs that, if evaluated as separate drilling projects, would be uneconomic. Cost Reduction This business driver is almost always considered in conjunction with one or more drivers. The purpose of the technology is to reduce CAPEX. The concept of multilateral technology is to incur only the additional cost of rig time, tools, services, and equipment needed to drill and complete an average deviated lateral of 300-1500 feet. The costs of mobilization/ demobilization, casing, and drilling to top of zone will essentially be borne by the main wellbore. A typical cost reduction model would have the multilateral well contributing up to twice the production, but only 1.5 times the cost of a monobore completion. Similarly, a trilateral may cost twice the monobore completion, but supply up to three times the production. Increased Reserves Additional reserves may be isolated lenses of pay or compartmentalized reservoirs. The degree of the compartmentalization will dictate the number of laterals and the wellbore geometry needed to optimally exploit the reservoir. Multilateral technology may also allow access to smaller or marginal reservoirs that, if evaluated as separate drilling projects, would be uneconomic.