Innovation in Drilling Using Replaceable Drilling Bit

Abstract

In conventional drilling a majority of drilling problems occur during tripping such as key seating and wall sticking. This leads to increase in rig time hence cost is unnecessarily high, especially in deep sea drilling. Conventional drilling techniques use rotary drill bits which need to be replaced depending on the formations encountered. If the formation is very hard, the bit has to be replaced by a diamond bit. These bit changes unnecessary increase trip time and eventually rig cost. This trip time which can take up to a day, especially for deep wells can be eliminated by using a novel "Replaceable Drill Bit" system. The concept of replaceable drilling bits is attractive for deep drilling because of the high rig costs and the lengthy round trips needed to replace worn bits. These bits are sturdy, capable of withstanding the high dynamic loads imparted by the vibrating drillstring and are capable of operating with highly abrasive drilling mud containing large amounts of sand and drill cuttings. Thus an entire hole can be drilled conveniently without frequent tripping operation to change the bit. Maximum efficiency can be achieved by this mechanism during drilling. Introduction Rotary drilling, the technique most commonly used today, has been continuously improved since it was first developed at the turn of the century. While great strides have been made in rig power, depth capability, bit life and penetration rate, this work has been centered on recovery of oil and gas reserves. Comparatively little attention has been directed to the harder, hotter crystal-line formations. To assure that future geothermal energy reserves can be economically exploited, new and more economical methods of drilling wells into harder formations must be found. The future exploration and development of the geothermal resources of the world will require a high level of drilling activity. Much of this drilling will be through formations as difficult as extremely hard igneous and metamorphic formations and wells will be drilled to great depths. Current drilling technology has been developed for the softer oil- and gas-bearing sedimentary formations. Even drilling in these is expensive and increases almost exponentially with depth. Since the difficulty of drilling increases with rock strengthdrilling for geothermal reserves will be much more costly than for hydrocarbon reserves. Description The primary objective of the downhole replaceable drill bit program is to reduce the footage costs of hard-rock drilling by increasing the net downhole life of the bit system, thereby reducing the number of trips required. A second objective that must be attained is to maintain or increase the instantaneous penetration rate compared to conventional bits. Both of these factors are significant contributors to overall drilling time, and therefore cost. In addition, a design is envisioned that can provide these improvements over a wide range of borehole diameters. A basic assumption in this program is that the replaceable bit must be directly compatible with existing rotary drilling rigs, drill pipe, drill collars, and liquid circulation systems. Power is delivered to the rock face by a combination of static loading and rotation of the bit. The drilling fluid pressure is used to cycle the replaceable cutter head when needed.