Development and Evaluation of Slimhole Technology as a Method of Reducing Drilling Costs for Horizontal Wells

Abstract

SPE Members Abstract Slim hole wellbores offer significant potential to reduce drilling costs in horizontal wells. This cost savings is especially important with the reduced capital budgets under current economic conditions in the oil industry. The savings can be achieved by the use of smaller drilling rigs and/or workover rigs, reduced casing sizes, minimized drilling wastes and other costs associated with hole size. However, the cost savings achieved from slim hole drilling can be offset by increased mechanical failures, reduced lateral hole length and lack of directional control. The paper reviews the advantages provided by slim hole (4-3/4" - 3-7/8" I.D.) wellbores as compared to the known capabilities of using reduced hole (6 1/2" - 6" I.D.) and larger hole (8 1/2" I.D.) technology. It uses information gained from horizontal drilling operations in the Austin Chalk Formation in the Pearsall Field in South Texas. Various improvements in directional drilling equipment are discussed as to their impact on reduced hole/slim hole drilling. The paper also discusses the decision process which must be used to determine if a slim hole well is applicable. It concludes that slim hole drilling offers great opportunity for cost reduction in drilling operations, but requires interactive involvement from all areas associated with the welt to prevent the limitations of a smaller wellbore from exceeding its benefits. Introduction Slim hole drilling involves drilling a major portion of the length of the well with drill bits less than 7 inches (17.8 cm) in diameter. It is not necessarily new technology. Slim hole drilling has been actively utilized since the early 1920's and was studied indepth in the 1950's by at least one major company which had an active slim hole development program. Both research and field data have shown that slim hole drilling vertical wells can be very cost effective. With current conditions in the petroleum industry where exploration activity is moving to more remote areas of the world, and in maturing developed areas where margins are declining, the need to reduce costs has become even more critical. In this climate, slim hole drilling is being proposed more often as a method of significantly reducing capital investment. Many operators and service companies are looking to variations of slim hole drilling to stretch Limited exploration budgets. The petroleum industry has reviewed many various slim hole techniques such as those used in the mining industry for ideas to improve slim hole drilling operations and further its use. However, utilizing the knowledge gained from slim hole vertical wells to reduce costs in horizontally drilled wells has not been simple. The limitations of downhole equipment often have precluded drilling lateral intervals of less than 6" (15.2 cm) in diameter. Until recently, cost savings that could be seen from reduced size tubulars would be more than offset by Lower rates of penetration or directional control problems. Today's economic and technological climate has changed that scenario. P. 681^