Lubricant enabled completion of ERD well

Abstract

Abstract Lubricants are often added to the completion or drilling fluid, in order to reduce friction between tubular equipment run into the well, and the wall of the well. This paper shows in detail how the addition of a lubricant to an oil based drilling fluid affected the lubricity significantly in the second of two comparable drill pipe runs, resulting in historically low coefficients of friction. The use of an ultra-low viscosity drilling fluid resulted in a clean metal to metal contact between the casing and the drill pipe, which caused high static friction. The selected lubricant was designed to stick to metal surfaces, and the result showed that the lubricant had a significant effect on both torque and drag forces. In the drilling phase, the apparent static friction factor decreased from 0.23 to 0.13 and the dynamic friction factor from 0.13 to 0.11. Comparing the two 8 ½″ sections drilled, the average off-bottom torque was reduced by 25 % after adding this specific lubricant to the drilling fluid. In selecting the lubricant, different lubricants were tested using a novel laboratory instrument capable of measuring the coefficient of friction at elevated pressure and temperature. These laboratory measurements proved to be consistent with the observed effect of the lubricants in the field. Introduction Statfjord Øst is a satellite field located northeast of the Statfjord main field. It has been shown to have pressure communication with the very mature main field (fig. 1). The Statfjord Late Life (SFLL) project is currently underway, where the main purpose is to reduce the reservoir pressure and to convert the main field to gas production. As a consequence, the reservoir pressure in Statfjord Øst will decrease, resulting in an accelerated reduction of well potentials and finally, (around year 2013) the wells would stop producing due to lift problems. Fig. 1. Statfjord main field and Statfjord Øst. The SFLL project would therefore result in lower recoverable reserves on Statfjord Øst. It was decided to mitigate this effect through the addition of a gas lift well in the Statfjord Øst field in order to both accelerate and prolong production from this prolific satellite. The costs of drilling the well from a semi submersible, and of installing gas lift facilities for a subsea well, were prohibitive. Consequently, the well was designed as an 8440 mMD extended reach well from slot C-33 on the Statfjord C platform, and it would become the second longest well ever drilled from a Statfjord installation (fig. 2). Originally, drilling fluid lubricants were not included in the plans. Simulations and empirical data showed that the well could be drilled and completed using existing top side equipment and conventional downhole fluids and equipment. However, severe drag anomalies during pipe running prompted the evaluation and subsequent successful application of friction reducers, both in the drilling and completion phases. The evaluation was carried out using a ‘HPHT lubricity tester’, in order to simulate the downhole properties of drilling fluids and their additives.