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.
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