Casing Window Milling With Abrasive Fluid Jet

Abstract

Abstract Methods for through tubing re-entry drilling of multilateral wells has a large potential for increasing hydrocarbon production and total recovery. One of the bottle-necks of this technology is initiation of the side-track by milling a window in the casing downhole. A new approach to this problem has been investigated in a joint industry project. An experimental set-up has been built for milling a 4" window in a 7" steel casing at surface in the laboratory. A specially designed bit developed at RF using abrasive jet cutting technology has been used for the window milling. The bit has an abrasive jet beam which is always directed in the desired side-track direction, even if the bit is rotating uniformly. The bit performs the milling with a combined mechanical and hydraulic jet action. The method has been successfully demonstrated. The experiments has shown that the window milling can be performed with very low WOB and torque. and that only small side forces are required to perform the operation. Casing milling has been performed without a whipstock, a cement plug has been the only support for the tool. The tests indicate that milling operations can be performed more efficiently with less time and costs than what is required with conventional techniques. However, the method still needs some development of the downhole motor for coiled tubing applications. The method can be used both for milling and drilling giving the advantage of improved rate of penetration, improved bit life and increased horizontal reach. The method is planned to be demonstrated downhole in the near future. Introduction Through tubing re-entry drilling with coiled tubing is a technology which has large potential for improving cost efficiency for increasing petroleum production and oil recovery. The technology has applications for multilateral drilling and for safe underbalanced drilling in a reservoir zone, especially in mature oil fields with low or decreasing reservoir pressure. Reliable and effective window milling for the drilling of multilateral wells in the reservoir is one of the most challenging aspects of this technology. Abrasive jet cutting is a technology in steady development, finding new applications in various industries. One reason for this is the development improved equipment for abrasive fluid handling. Another reason is the special features this technology has for cutting, for example the possibility to efficiently cut hard materials with very low forces acting on the cutting tool. Abrasive jet technology has previously been investigated in connection with oil-well drilling. Previous investigations have proven high efficiency of abrasive jet systems, but equipment reliability has been a limitation for application of the technique. However, with development of improved technology and new applications this does no longer seem to be true. There are special applications for this technology in drilling and well operations, especially in combination with coiled tubing. A coiled tubing drilling system has a limitation in available downhole force and thus can benefit from this technology. A casing window milling system based on abrasive jet cutting technology developed in a joint industry effort is presented in the following. The method can be used in combination with coiled tubing, as well as snubbing and conventional drilling equipment. The abrasive jet milling system The conceptual solution for the coiled tubing window milling system is shown in figure 1. The coiled tubing enters the well through a production tubing. The window milling operation is performed in casing in the reservoir zone. A cement plug is placed in the casing downhole prior to the window milling operation. The hole drilled in this cement plug by the milling system will give sufficient support for the milling system to be able to penetrate the steel casing. The window milling system uses abrasive jet technology for an efficient initial cutting and subsequent milling of the steel casing. An abrasive injection unit at surface adds abrasive particles to the fluid which is pumped downhole through the coiled tubing. A downhole pressure intensifier can be used to further enhance the efficiency of the operation. P. 45