Low Cost Slim Hole Drilling System

Abstract

SPE/IADC Members Abstract Interest in reducing the cost of exploration in frontier areas and in areas of special environmental concern has given rise to a variety of initiatives to develop ‘slim hole’ drilling systems and down hole tools. The market over capacity of conventional rigs offered at unrealistic commercial rates masks the real cost of operating heavy drilling equipment. This acts as a disincentive to the development of smaller innovative drilling rigs and associated equipment and the development of a smaller scale drilling system that has wide acceptance in the industry. Furthermore, funding for development of such systems has been sadly lacking. In response to a contractual commitment, an opportunity arose to design and construct a small, low cost drilling system suitable for a range of slim hole and downsized drilling scenarios. In this particular case, the equipment was required to drill both vertical and slant boreholes with slant angles up to 45. The drilling unit and associated equipment combine a blend of oilfield and mining ideas with the objective of demonstrating that a low cost unit could satisfy the requirements of the industry for frontier drilling. The drilling unit is capable of both conventional destructive drilling up to 17-1/2 in diameter and continuous coring using heavy duty systems up to 6-1/4 in hole size. The singles rig is 100 ton capacity with a rotary capability from the top drive system of up to 400 rpm which gives a slim hole capability of over 3500 m. The mechanised pipe handling system includes a hydraulic clamping device within the top drive head and an elevating and extending catwalk with hydraulic power breaker capable of breaking 8 in drill collars. The handling system will accommodate 13-3/8 in Range 3 casing. Triplex mud pumps, power pack and generators are housed in acoustic containers. The rig and associated equipment is designed to oilfield standards and all pressure lines are rated to 5000 lb/in2. A BOP handling system is included especially to cater for slant drilling and a hydraulic crane mounted at drill floor level together with a tugger winch provides general handling facilities around the rig. All main rig units are configured to 6 m ISO container standards for ease of shipping and port handling including mud tanks. The rig includes a comprehensive computerised rig instrumentation system with a local computer network for the site and a sensitive automatic drilling facility operating through the hydraulic drawworks winch control system. The paper describes the background philosophy, the equipment and the initial operations since commissioning the equipment in June 1994. Introduction Recent interest in reduced size drilling systems for oil and gas exploration and development has given rise to a number of initiatives to develop ‘slim hole’ systems and downhole equipment. The idea of downsizing is not new and indeed many of the wells drilled today as ‘slim hole’ were considered common in the past. P. 463