A New Method for Torque and Drag Retro-Analysis to Obtain Accuracy to Compute the Friction Factor for Wells in Severe Drilling Scenarios of Pre-Salt Fields

Abstract

Abstract New technologies and methodologies for estimating torque and drag (T&D) response during directional and horizontal drilling wells are constantly being researched in the literature. Classical methods developed in the 80s are still used nowadays. However, their approximations involved may incur significant errors during the well drilling design and operations. In contrast, using numerical methods may increase the computational costs of a well plan and result in unfeasible designs. A methodology to determine the friction factor based on retro-analysis of data from drilled wells is presented to support well design in severe drilling scenarios, such as the pre-salt of Brazil. The systematization of the T&D retro-analysis process makes it possible to compose a database and consequently allows to determine the friction factor more accurately, as well as the analysis of the variables' influence on it and results in more accurate decision-making on resource planning and well design, such as: use of power section in the BHA, drill string assembly, maximum casing extension, back-reaming operation, rig type choice and feasibility of wellbore completion. A case study of planning and design in Pre-salt of Brasil is presented, in which the wells have very deep final depths and/or challenging trajectories, the drill string and the rig are subjected to efforts that approximates their operational capacities, even when considering the best on the market. Therefore, in these scenarios, a high accuracy of the friction factors values, used in the design phase, is crucial for planning and execution success. The methodology to determine the friction factor based on retro-analysis of drilled well data results in more realistic and accurate friction factors.