This paper describes a case study of planning, drilling, completing and production of an extended reach horizontal infill well in the giant Al Shaheen oil field, offshore Qatar. The completion has been designed with three surface controlled zones. The completion is supplemented by a straddle on mechanical open hole packers to isolate a section which has higher risk of pre-mature water breakthrough. This completion provides flexibility for selective production, production testing and performance monitoring. Seven infill wells were planned in the Shuaiba formation for optimization of oil recovery. The first wells were brought online with higher than expected water cuts. A completion was designed for the fourth well in the area to improve reservoir management and liquid handling. The well was successfully drilled with a long step out in order to avoid installing a cemented liner for well spacing purposes in the inner section. The completion was designed based on the downhole logs and record of mud losses while drilling and was installed to 15,000ft. The completion consists of surface controlled sliding sleeves and a ball valve complemented by a pressure gauge and chemical injection. The completion was installed inside a predrilled liner which separated the liner section into zones by timer set mechanical open hole packers. In addition a straddle was installed to isolate a natural fracture zone in the outer part of the well. The completion was run and installed successfully and selective production testing has been conducted. The results show that the three zones have water cuts ranging from 5 to 50%. Selective control of the completion helps to optimise oil production and minimise water production as an integral part of an intelligent field management strategy. Net gain from this completion amounts to some 4,000 stb/day.

fax 01-972-952-9435. AbstractThe idea of drilling single diameter wells has been debated for a number of years. And in recent years, the dream of monobore wells is taking form thanks to the development of new technologies. The use of expandable tubulars and the drilling with casing system are the most favoured processes. This paper discusses the possibility of coagulating these two technologies in an attempt to achieve maximum economic and productive efficiency. The system consists of the usual assembly for drilling with casing, which uses the top drive mechanism, and an expansion cone (mandrel) installed above the drill lock assembly. The expansion cone is operated from the surface through the rotary table. The operation involves drilling to the casing depth using the drilling with casing assembly, and then bringing the expanding cone into action. The expansion procedure starts by conditioning the string and pumping in the expanding fluid through the expansion mandrel. It is caught in the area between the mandrel and the drill lock assembly by closing the bypass valves in the latter. Thus the pipe joints above the drill lock assembly are expanded by the normal procedure, till the mandrel reaches the surface. The mandrel is pulled out, and subsequently the drilling with casing BHA is retrieved by a wireline.This procedure makes use of the economic savings achieved in case of drilling with casing and the productive maximisation which is achieved for expandable tubulars. By using the expandable tubulars at shallow depths, more casing strings can be accommodated resulting in production of deep formation(s). This procedure also involves a reduction in time related to tripping operations which was earlier associated with the drill string assembly.More importantly this new technology finds it major application in extended reach deep water drilling, where ultra-slim wells need to be drilled to reach the formation. This technology requires a class three or four drilling vessel instead of a conventional class five vessel, thus reducing the drilling costs substantially. These two technologies are currently being used in independent fields and there is no published evidence about the combination of these two operations. Now as this method is researched further, new and more improved versions of the same can be developed.

TX 75083-3836 U.S.A., fax 01-972-952-9435. AbstractIn 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.

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.

In conventional vertical drilling, the drill string is tripped in, allowed to drill to the predetermined depth and tripped out so that a bit of a smaller diameter can be attached to continue drilling the hole. Extendable arm drill bit is essentially a rotary drill bit in which the roller cones can be extended so that the diameter of the bit corresponds to the required diameter of the hole to be drilled. This extension is done hydraulically by diverting some of the pressure of the circulating drilling mud to compress an assembly which would push down the roller cones, thus increasing the diameter. Now as drilling continues, the diameter of the bit can be adjusted by diverting a lesser amount of circulating pressure on the bit thereby "contracting" it to achieve a smaller diameter. It could be imagined like a tripod standing on its three legs. The idea behind this proposal is to save the time, power and the cost of tripping operations of the drill string to change the bit to a smaller diameter one, by reducing the frequency of tripping the string, if not completely eliminating the process. This would result in an increase in the overall rig efficiency, both in terms of time and mainly money. Thus, the time and money saved can be diverted, if required, towards problems arising due to unexpected hole problems and pipe stuck-ups. This paper gives the description of the most suitable design of such a drill bit and the possible modifications of this concept to be applicable in future developments. Introduction Through the history of oil well drilling, individual concentric lengths of pipe are used to line the borehole. This process results in stability of the hole and avoiding the hole from caving in. But it also leads to structural redundancy of the casing that is used as a bore-hole liner and results in an increase in the cost of both the material and logistics involved. During the drilling operation, there is a need to isolate sections of the well depending upon a variety of geological factors which range from abnormal pore pressure to wellbore instability to hydrocarbon or water bearing zones. From the time rotary drilling was employed, wells have been drilled in a step-wise manner i.e. drilling a larger diameter hole at the surface and proceeding to the reservoir with a receding hole diameter. The bore-hole drilled is cased in between changing of the bit to drill a smaller diameter hole. A single diameter bore-hole cannot be drilled throughout its entire length due to certain parameters arising largely due to geothermal pressure gradients. But still, two techniques, namely the expandable tubulars and drilling with casing methods drift apart from the traditional drilling operations. In cases where there is an uncertainty about the bore-hole instability, simultaneous lining or casing of the hole alongside drilling removes some concern. But this method, which is employed in casing while drilling operations, reduces the annular space between the casing and the bore-hole as it involves drilling with concentric casing strings rather than the traditional drill pipes. Certain grades of steel have much greater ductility which allows adequate plastic deformation to be achieved without much harmful work-hardening, in such a way that it is feasible to increase the diameter of a pipe uniformly and without any uneven thinning of the cross section. The development of pipe connections which are capable to accommodate this increase in diameter has brought the concept of mono-bore wells in the limelight. One of the convenient methods for drilling a mono-bore well is employed by the casing while drilling method. The drilling BHA passes through the casing of restricted diameter to get attached at the bottom of the casing to drill till the pre-determined depth. Later the BHA is retrieved by wireline at the end of drilling. But since the BHA has to pass through the casing, the size of the pilot bit and the underreamers used suffers. Also a smaller size of motor is used which reduces power output and increases sliding drilling ratio due to its flexibility.