Percussion drilling technology was considered many years ago as one of the best approaches for hard rock drilling. Unfortunately, the efficiency of most hydraulic hammer (HH) designs was very low (8 percent maximum), so they were successfully used in shallow boreholes only. Thirty years of research and field drilling experience with HH application in former Soviet Union (FSU) countries led to the development of a new generation of HH designs with a proven efficiency of 40 percent. That advance achieved good operational results in hard rock at depths up to 2000 m and more. The most recent research has shown that there are opportunities to increase HH efficiency up to 70 percent. This paper presents HH basic design principles and operational features. The advantages of HH technology for coiled-tubing drilling is shown on the basis of test results recently conducted in the USA. [S0195-0738(00)00101-1]

Significant part of axial compression load transferred to the bit while drilling of wells with high zenith angles is resisted by service drill pipes. By the action of static critical load, buckling of drillstring occurs initially in the shape of a sinusoid and subsequently, as the load increases, in the shape of a helix. Drillstring rotation promotes the occurrence of critical modes. As a result the drillstring can start snaking motion at the low side of the hole. When the rotary speed grows, whirling of the drillstring can occur with axial load much lower than the buckling load. In this paper, a nonlinear mathematical model of lateral vibrations of a rotating drillstring in straitened space of a straight inclined hole is proposed. A numerical method to solve drillstring motion equations has been developed that allowed to reduce time of computation. This made it possible to conduct a detailed study of how the main drilling parameters (compression load, drillstring rotary speed, hole angle, friction factor, etc.) effect drillstring motion in the well. Results of the study may be used to choose drillstring operation modes for rotary drilling of inclined and horizontal wells.

Drilling shallow stratigraphic boreholes in deep water is an important component leading to reduction of exploratory costs. The Complete Coring System (CCS), using special retrievable tools and large diameter aluminium drill pipes has proved to be a possible way to perform this task. CCS combines experience of Russian continental scientific drilling techniques with ODP research efforts and is represented by several coring methods along with sequential drilling using a retractable bit and logging without tripping of the drillstring. Separate units of the system have been used both onshore and offshore in different geological conditions. In 1993 OCS has been utilized for drilling in 1500 m water depth offshore Norway. Introduction Generally the accepted way of the new offshore area investigation for oil and gas or other deposits consists of several stages which include:Geophysical survey;Sampling and coring with soil investigation;Prospecting or exploratory drilling with coring, logging and (probably) testing the hole;Development drilling for production Every stage needs a certain type of vessel to conduct the work. The most expensive and complex is stage "C" because an unknown geological structure will have to be drilled from the "full scale" platform. That means: large diameter hole spudding; running the casing strings; riser and BOP system application. But the risk of unexpected problems and negative results are always present. P. 823^

This paper presents the experience gained with the use of special large diameter aluminum drillpipes (ADP) in the Atlantic Ocean, Norwegian Sea, Gulf of Mexico and Gibraltar Straight. The maximum water depth achieved was 1616 m. Both rotary and down hole motor drilling and coring techniques have been used for drilling and coring in variety of formations - from soil till hard rocks. Various types of retrievable tools are available to offer a spectrum of possibilities. Introduction Deep water exploration for oil became a prominent field of strategic research efforts during past years. To prove the evaluation of future oil and gas provinces productiveness, soil samples and rock core need to be recovered and investigated. So-called stratigrafic boreholes can be drilled with relatively small drilling vessels normally used for geotechnical purposes. However the conditions of such drilling operations are beyond the capabilities of such vessels when the water depths at the location exceed 500–600 meters. A solution to this is the usage of a light weight aluminum drillstring. The drill pipes described combines the large Russian experience in design, manufacturing and application of aluminum drill pipes for oil field and continental scientific drilling of super-deep boreholes. The 6-5/8" OD internal flush pipes provides several coring methods along with sequential drilling and logging without tripping of the drill string. Four years offshore operating experience confirmed the analytical and experimental data. The results presented in the paper lead to a conclusion that use of aluminum alloys for offshore exploratory and development drilling from floating platforms holds much promise. Some result of drill string behavior analyses on the basis of analytical model are presented as well. Aluminum Alloys and ADP Applications Background Aluminum alloys, one of today's most important and efficient construction materials possess a number of specific physical and mechanical properties that are in favor of steel drill pipes, which is the traditional material used for the manufacture of drill pipes and other elements of offshore drilling systems. Issues related to the use of aluminum alloys for the manufacture of drill pipes gained close attention and became the object of detailed research in Russia when drilling began of directed extended reach and horizontal wells and ultra deep wells. Furthermore the extension of drilling to areas with difficult environmental conditions and limited infrastructure required the reduction of transport costs of equipment and materials. This was also true for offshore drilling. It was realized that these problems could be alleviated by the use of lightweight drill pipes. Experience gained in the design and application of ADP in Russia may be relevant to future applications of such technology to offshore drill strings. As the offshore drilling in deep water areas around the world has been significantly expanded in the past decade, such developments could plainly benefit from lightweight drill strings. Table 1 gives the main physical characteristics of three types of aluminum that were selected for ADP production. The modulus of elasticity, which to a large extent determines allowable deformation characteristics of structures, is only one third the modulus of steel. The weight in water of aluminum is only one quarter that of steel, whereas the strength, particularly of the alloy 1953 T1, is about half that of high strength steel. ADP made of D16T alloy were widely used for drilling wells at all industrial depths and under various geological and technical conditions. P. 219^

While drilling deepwater stratigraphic wells in the water basins with ice sheets, drillers usually encounter the problem of a drillstring protecting from ice loads. One of the methods of the drillstring protection from ice impact provides for clearance installation of an ice pipe in the drilling vessel unit moonpool with the pipe bottom several meters below the keel. The paper suggests the numerical-analytical method of the stress-deformated state calculation for the drillstring and the ice-protection pipe with allowance for contact interaction between the drillstring, the ice protection pipe and the moonpool wall. The ice load value is determined based on the condition of equality between the kinetic energy of a moved ice floe and the elastic energy of the “drillstring – ice-protection pipe” system. The principle of the minimum potential elastic energy is used for calculating the system equilibrium configuration, with account to constraints of the system element displacement. The method of coordinate-by-coordinate descent is used to find a solution for the conditional minimization problem. The developed method is employed to evaluate the efficiency of the ice pipe design to be used while drilling deepwater stratigraphic wells from the Botnica multi-function icebreaker in the Arctic region under the International Ocean Drilling Program (IODP). The study showed that the suggested ice pipe design was capable of withstanding impacts of ice floes moving at 1.5 m/sec with thickness of 1 m and with diameter up to 3.5 m.