Remaining oil and gas resources situated in easily accessible reservoirs are continuously dwindling, forcing the drilling industry to extend the range of possible targets for production activity to deposits located at considerable depths and a long way from drilling sites. With significant increase in the price of oil, a large number of deposits whose development was previously considered non-economical became suitable for exploitation. Most of these deposits lie offshore and need a borehole of considerable length to reach them from land. Recently the industry experienced a rapid increase in TMD of ERD wells, and reached the record of 11,282m TMD at Sakhalin-1 project in Russia. Several other ultra-long ERD wells include 11,278m TMD (10,728 m displacement) at Wytch Farm M-16 in UK; 11,184 m TMD (10,585 m displacement) at CN-1 in Argentina; 9,082m TMD in Visund, North Sea and etc. Drilling of such long wells, where conventional technology is stretched to its limits, is extremely challenging. Most critical of such challenges is increase in weight of the drill string, leading to considerable growth of drag. In ultra-long wells, the drag may rapidly reach values making it impossible to continue drilling without either reducing frictional forces or reducing the gravity force component acting between the contact surfaces. Reducing the weight of the drill string provides great benefits in ERD operations.

One of the solutions for extending the limits of horizontal well drilling is the replacement of conventional steel drill pipe with light alloy drill pipe. This pipe contains a number of superior properties offering important benefits. The most important of them is decrease of drag and torque in horizontal sections, which reduce the possibility of buckling initiation. Aluminium drill pipe (ADP) has extensive productive operational experience in drilling various types of wells. One of the outstanding achievements gained with utilization of ADP was reaching the world record depth of drilling at Kola Ultra-deep Well in 1990. The drilling of this well was performed by use of downhole motors with simultaneous drill string rotation, which predominantly consisted of ADP. The drilling of this well presented a huge amount of operational experience, which in turn was effectively used in drilling less complicated wells. In fact, ADP usage averaged about 80% of all drill pipe in operation in the Soviet Union by 1980-s.


Severe-ERD wells with a TMD/TVD ratio >3 were first enabled through the development of Rotary Steerable Systems (RSS), in combination with refinement of conventional operating procedures and conventional technologies. There are only a few examples of implemented step-changing technologies besides RSS, specifically developed for deviated wells. Sequentially installing expandable drilling liners without reducing inner diameter is one example of a potential future technology that may be utilized to secure drilled sections in ERD. The key to success in most ERD projects today is solid detailed planning with regards to ECD management, hole cleaning and ability to handle occurring challenges such as lost circulation and well control scenarios. It is now time to focus on step-changes in improving ERD technology, with drill string material selection as one of the enablers for >17 km MD wells with horizontal displacement of >15 km.

Series of simulations were run in order to evaluate the theoretical length limits of Extended Reach Drilling. Initial data for DS calculations and hydraulic losses in a well was taken in accordance with data for a well in North Sea. We performed calculations using special-purpose DDTBHC software.

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