The interest in the re-entry of existing wells for the purpose of drilling multi-laterals is growing. This paper discusses the options available for drilling multi-laterals. The paper also discusses where completion technology for multi-lateral wells is heading in the future.
The reasons for drilling multi-lateral re-entry wells vary from well to well, but always comes down to one point: economics. If it is possible to increase the production of an existing well with a minimum of cost, then a multilateral should be drilled. The cost effectiveness of a multilateral program goes beyond the scope of this paper and will not be discussed in great detail.
One of the primary purposes of re-entry drilling, in the past, was to drill to new targets from an existing wellbore to save the cost of the vertical section of a new well. Due to advances in completion and drilling technology, the idea has advanced to the point where these additional targets can be drilled without losing the existing production interval. Additional targets may be entered, or additional horizontal sections can be drilled from the existing wellbore to increase the savings over the traditional method of one production casing per wellbore The savings associated with drilling multi-lateral sections out of existing wellbores become even more significant when the work is performed offshore. Utilizing existing slots to intercept one or more additional targets from an existing wellbore reduces the cost of adding slots to the platform.
1) There are various types of multi-lateral wells that may be drilled and completed. The first is a simple multileg, open-hole completion with a single string packer. This type of completion has been used in the Austin Chalk formation in Texas. In this completion, the original perforated interval is abandoned and the casing is milled up at the appropriate level for new drilling. The new sections are drilled through the milled section and completed open hole. A packer is then run in the casing above the open-hole section. and the well is completed. The advantages of this type of completion are the cost savings of the casing in the open- hole section and the simplicity of the drilling operations. The disadvantages are the lack of access to the different laterals and the possibility of hole collapse. (See Figure 1.)
A more complex method of drilling and completing the multiple open-hole multi-lateral is to use an open-hole whipstock packer to drill the upper lateral.