New Downhole Tool for Coiled Tubing Extended Reach

Abstract

Abstract Extending the reach is one of the main challenges for coiled tubing operators, as illustrated by the multiple efforts to develop downhole traction devices for coiled tubing (CT). This paper presents a simple, yet reliable and efficient tool for extending the reach of CT. The tool, called CT Friction Drag Reducer (FDR), is based on a unique patented concept, and uses fluid flow to generate axial oscillation in the CT and bottom hole assembly. As a result, time-averaged friction forces can be reduced significantly. Calculations based on a simple physics-based model predict that the reach can be extended by over 3000 meter in a horizontal well with a measured depth to true vertical depth ratio (MD/TVD) greater than 2.0. Model results match well with full-scale tests. The tool will normally be integrated as a part of the bottom hole assembly (see Figure 1). The FDR tool has been developed and tested at RF- Rogaland Research (RF) as part of a joint industry project (JIP) with Saga Petroleum ANS and Shell International Exploration & Production B.V. as main industrial sponsors and with co-funding from commercial investors. The FDR tool has an outer diameter of 3.5 inch, is 1.2 meters long and is designed for flow rates in the region of 100 to 900 liters per minutes. Laboratory tests at RF demonstrate the feasibility and functional efficiency of the concept. Full-scale tests using a 7-inch internal diameter horizontal surface loop at RF have proven the friction reducing efficiency of the concept. In several tests with 600 meter of 1.75 inch coiled tubing and a bottom hole assembly weighing 600 kg, the friction force during run-in and pullout from the 7-inch test well was reduced by up to 90 %. In one case of run-in, the measured friction reduction was 94%. An acceptance test with 2-inch CT has been conducted at RF using the CT unit at the Well Intervention Test Center to demonstrate and document the endurance of the FDR tool. The technology will aid in CT intervention and drilling operations, but can also be used in conventional operations such as placing liners in extended reach wells and pipeline operations. Introduction The application of extended reach technology has resulted in extended reservoir drainage, increased production rates, improved production management and improved field economics. Drilling and completing extended reach wells are common operations worldwide and have developed rapidly in the Norwegian, Danish and UK sectors of the North Sea. However, current coiled tubing techniques and equipment have not developed rapidly enough to keep up with the operational challenge which these extended reach wells represent. Due to the high angles of the long tangent sections combined with the TVD of the reservoir, limitations on the horizontal displacement occur because of the frictional forces between CT string and borehole while running CT. This causes helical buckling and can lead to lockup of the CT, thereby limiting the reach. The onset of buckling can be postponed by reducing the frictional contact force between the coiled tubing and wellbore leading to additional reach. This can be achieved by introducing axial oscillations to the coiled tubing string, and thereby reducing the effective friction factor between the coiled tubing and wellbore. Axial oscillations are generated by pumping fluid down the CT and through the FDR tool. During the development of this concept all three modes of oscillations were considered, axial, torsion and lateral oscillations. It was concluded that the axial mode proved to be the most suited one, mainly because axial oscillation are more easy to generate in a controlled manner, but also because its effect on friction is greater. The FDR tool is a double acting hydraulic cylinder with mechanical valves that cause a minor reciprocating movement. A set of springs facilitates the operation of the valves. The mass of the bottom hole assembly below the FDR tool directs the majority of the oscillating action up the CT string.