The Practice and Evolution of Torque and Drag Reduction: Theory and Field Results

Abstract

Introduction In the past two decades, drilling extended reach wells (ERWs) has become commonplace in the petroleum industry as companies seek to drill deeper and further to optimize the oil and gas production in the target field. ERWs are defined as wells that have two times more horizontal stepout than true vertical depth. Drilling longer horizontal sections allows more area of the reservoir to be exposed as well as less surface area disruption. As a result, with the global trend moving toward drilling ERWs, engineers can no longer ignore the high torque and drag forces expected in the well. There are numerous methods and tools engineers have developed to lower torque and drag forces and ultimately allow the drill string to drill to total depth (TD). However, only a few have proven to be a worthwhile investment. An early high-visibility, large scale ERW drilled was the Wytch Farm project conducted by BP Exploration Operating Co. Ltd in 1993. The company originally considered creating an artificial offshore island; however, it was neither economical nor environmentally friendly. Instead, they drilled 10.1 km or 33,136 ft horizontally from an onshore platform to the target of interest. The well was known as the longest ERW drilled at the time. It is notable that back then, without knowing as much about torque and drag as we do today, they were able to control the torque and drag within the limitations of the drilling components. The mechanisms they used that allowed them to drill such a hole included a combination of hole cleaning improvements and mechanical friction reduction. This paper focuses on the different torque and drag reduction methods utilized in the past and how individual methods have proven to be worthwhile for engineers to use. The methods that are discussed in this paper include wellpath design, light weight string components, lubricants, hole cleaning, co-polymer beads, and mechanical friction reduction tools. History Of Torque & Drag In the past, engineers rarely encountered torque and drag problems simply because the wells drilled were not as challenging as the wells drilled today. As "easy to drill" conventional oil and gas wells have diminished, engineers are drilling wells and sidetracks that are more complicated and deeper than ever before. This results in higher torque and drag forces during downhole operations. Since the Wytch Farm well was successfully drilled in 1993, operating companies have challenged the limitations of the tubulars, the rigs, and the personnel in hopes of discovering reserves that were not accessible in the past. This use of onshore extended reach drilling (ERD) to avoid the creation of offshore islands has been repeated many times, including well known wells in Sakhalin Island.