Multi-lateral drilling and completion techniques involving cased primary and lateral well-bores have become increasingly prevalent in the oil and gas industry over the past five years. The experience gained in this time has permitted technological advances which now allow operators the flexibility to plan for increasingly complex multi-lateral applications. An effective planning process is essential to the successful drilling and completion of every multi-lateral project, whether it be a single open hole lateral application with no reentry or isolation requirements or a complex combination of multiple laterals in different formations requiring fully selective reentry and isolation capabilities.
This paper discusses the many technical issues which must be considered when planning the drilling and completion of multi-lateral wells.
Consideration is given to the selection of the optimum drilling and completion systems for particular applications, and includes a comparison of the advantages and disadvantages of pre-milled casing window systems with those of downhole window milling techniques.
Various drilling and completion issues are then discussed in detail as they relate to the planning of multi-lateral wells. These issues include well profile considerations; cementing options; reentry and isolation requirements; well control considerations; constraints imposed by the technology and the importance of contingency planning. A case history which serves to illustrate the importance of a comprehensive planning process is presented.
The paper presents a set of guidelines which are based on a continually increasing level of experience gained during the installation of over 100 casing window systems in various applications worldwide in addition to the extensive bench testing which has been carried out on these systems. This experience has resulted in enhanced planning processes which lead to reduced risk when implementing multi-lateral systems.
The successful implementation of multi-lateral systems is heavily dependent upon a comprehensive planning and review process. In every application a large number of factors are involved which must be taken into consideration when planning a multi-lateral well. The constraints imposed on the well design by the limitations of the system selected should be clearly understood and factored into the planning process. The purpose of this process should be to minimise the risk of problems occurring during the deployment of the system. To that end, careful attention must be paid to the smallest details, to ensure that nothing is left to chance and every operation is carried out as smoothly as possible.
Although it is recognised that a large number of multilateral wells have been drilled utilising open hole sidetracking techniques, the discussion will concentrate on the newer systems which involve drilling laterals from a cased primary well bore, with the ability to line the laterals. As the majority of these applications involve the utilisation of pre-milled casing window systems the emphasis will be on the technical issues associated with planning the implementation of these systems. However, it will be evident that a number of these issues are common to all multi-lateral applications whatever method or system is selected.
Once a candidate reservoir or well-site has been selected, experience has shown that a multi-disciplinary approach should be taken from the earliest stages of the well planning process. In many instances special multi-lateral teams have been formed in order to ensure that the planning and implementation of projects have been carried out successfully. P. 45^