Chemically-Enhanced Drilling with Coiled Tubing in Carbonate Reservoirs

Abstract There has been a dramatic increase in the use of continuous reeled tubing (coiled tubing) for drilling operations. Much of this increase can be attributed to improvements in the quality and dimensions of coiled tubing itself – pipe sizes have steadily increased over the years from 1 inch OD to 3 ½ inch OD and bigger. Other developments have included improved downhole motors and, for directional work, sophisticated survey and orienting tools that can be controlled, in real time, from surface. Despite these developments, CT drilling is still applied to very few wells, or a tiny percentage of the total drilling market. There are many reasons for this including high equipment and personnel costs, low rates of penetration (ROP), and issues related to the reliability of high-cost "smart" bottom hole assemblies (BHA's) needed for directional work. The idea that CT drilling would offer a cheap alternative to conventional rigs is, and probably will remain, an unfulfilled pipe-dream. However, CT drilling certainly has its place, particularly for vertical well deepening and for slimhole multilateral work. The method presented here provides the opportunity to improve the efficiency and lower the cost of such operations. This paper describes a technique that we call Stimulation While Drilling (SWD), a drilling method that is particularly applicable to the use of coiled tubing. In particular, the method is intended for use in the drilling of multiple short, lateral drainage holes originating in the main borehole and extending outward radially through the reservoir, at one or several depths. However, any hole, including the main borehole itself, can be created using this technique, depending on the lithology. This ability to make large multilateral conduits, at high speed, in underbalanced conditions, if desired, and with no drilling damage offers significant advantages for well construction and completion, particularly in hard carbonate reservoirs.