Key Factors in the Development of High Circulating Temperatures in Horizontal HPHT Wells

Abstract

Abstract One of the major limiting factors when drilling horizontal HPHT wells is the circulating temperature of the mud exceeding the downhole tool specifications. This paper explains the key contributing factors to the development of high circulating temperature in deep horizontal wells and the major well design components that need to be addressed to establish the feasibility of the well. In horizontal wells, frictional pressure loss increases with the measured depth (MD), whereas geothermal temperature remains constant. This causes a progressive increase of the downhole circulating temperature to the extent where it can become higher than the static temperature, and traditional ways of reducing the downhole mud temperature become less effective. The circulating temperature management described in this paper is based on a comprehensive approach, where the key contributing factors were reviewed to address this issue. This review includes frictional pressure loss management, particularly through the drill string, BHA design, and drilling parameters optimization. The industry has traditionally relied on surface mud cooling systems and a strategy of premeditated circulation to cool down the BHA equipment to manage the downhole mud temperature, with mixed results in horizontal wells. Implementation of the comprehensive approach in managing the circulating temperature enables more efficient and consistent temperature management. This paper reviews one horizontal HPHT well, where the downhole circulating temperature was managed through the reduction of frictional pressure loss. This permitted drilling and logging of the well to be completed within the tool temperature rating. Based on the observations gained from this well and a number of other wells not included in this paper, a conclusion was drawn that the feasibility of long reach horizontal HPHT wells heavily depends on the ability to effectively manage the frictional pressure losses in the system. This requires a good understanding of the well temperature environment, mud behavior under the expected temperature and pressure in the high angle section, accurate estimation of heat exchange between the mud-and-pipe and mud and the wellbore, mud coolers efficiency, and BHA component specifications. The paper proposes to address the common issue of excessive circulating temperature in horizontal high-temperature wells from an engineering standpoint through the implementation of the comprehensive approach in managing the frictional losses during circulation. The introduction of this approach in the well design process should enable longer reach horizontal high-temperature wells, which are currently limited due to downhole tool temperature ratings.