Utilizing Coiled tube rig for mineral exploration application

Abstract

Mineral exploration is in a race to employ drilling technology that can perform the exploration and drilling investigation in a fast and inexpensive manner. After an extensive study of the available drilling technologies in the market, coiled tubing was chosen as a tool to be employed for mineral exploration due to its flexible mobility and ease of operation with minimum number of personnel. Since coiled tubing technology is primarily used in oil and gas industry, it was important to re-design the coiled tube rig to drill hard rocks in a fast and feasible manner. The main requirements were to drill the smallest feasible hole diameter and go as deep in the ground as possible, in the shortest reasonable time. The drilled rock particles, cuttings, are to be collected and analysed at the surface for their metal mineral contents. The process also needs to be repeated multiple times at different locations for mapping, without the need to change the tube on the rig due to failure or potential failure. The focus of the new designed coiled tube, for drilling and mineral exploration, is three fold. First is to increase the rate of penetration (ROP) in drilling by designing a small high speed turbo motor. Second is to determine the controlling parameters of cuttings transport to effectively lift the cuttings to the surface for analysis and third is to minimize the overall weight of the rig for manoeuvring and to prolong the life span of the coiled tube string. In this paper, a small downhole turbo motor, 5cm outer diameter, is designed to achieve a rotation speed of up to 10,000 rpm to fit on a small bit, coiled tube drilling assembly. The motor design utilised multiple finite volume and finite element analysis software for fluid flow study and fluid structural interaction analysis.The paper is also introducing the concept of flow slurry loop that is designed to lift the cutting particles to the surface for mineralisation analysis. The controlling parameters of the cuttings transportation are the particles physical properties such as size, density, concentration and shape, as well as the rheological properties of the carrying fluid, drilled hole angle, as well as the fluid flow rate and flow dynamics within the annulus gap between the coiled tube and drilled hole. Such parameters are addressed via experimental work as well as numerical analysis. The paper is also presenting the selection and testing procedure of the material type for the coiled tube string. The tube needs to be light in weight for rig transportation and to drill few dozens of drill investigations holes before failing due to fatigue. A fatigue bending machine is designed to test the endurance limit of candidate materials for coiled tube string and performance index methodology is followed for material selection of the optimum material. The coiled tube rig is designed to be light in weight for transportation and relocation. It is also required to speed the drilling operation with the minimum foot print and will reclaim the drilled rock particles for mineral composition analysis at the surface.