Improvement of Drilling Operations on Horizontal Wells at the Orinoco's Heavy Oil Belt, Venezuela

Abstract

Abstract Stuck pipe incidents and excessive torque and drag have been common problems encountered while drilling horizontal wells in the Orinoco Oil Belt which contains Venezuela's largest heavy oil reserves concentration. These incidents have been attributed mainly to high levels of friction between the drillstring and the heavy oil sands. To help prevent sticking, a common practice has been to add 10 to 20 vol% of diesel to the water-based fluid when drilling the horizontal sections. Open hole displacement of mud by diesel had also has been used to free stuck pipe. However, many of these incidents have resulted in the loss of the bottomhole assembly and the need to perform sidetrack operations. Typically, engineered fluid solutions have been required to solve friction issues related to horizontal sections and tortuous well geometries. Additionally, a hydrocarbon-free and non-damaging lubricant option has been necessary to help prevent excessive torque and drag when drilling 2D and 3D well trajectories with a water-based fluid. Recently, a viscoelastic drilling fluid comprised of a blend of special synthetic oils and surfactants has helped reduce the coefficient of friction in water-based mud by as much as 50% without adversely affecting the rheological properties, as well as dissolving bitumen and preventing emulsification of the heavy oil and sand. After the lubricant treatment, torque and drag values experienced while drilling highly deviated sections through unconsolidated sands at instantaneous penetration rates of up to 1,300 ft/hr have decreased from 18,000 to 12,000 lbf-ft. Also, because no stuck pipe incidents occurred and clean-up trips weren't required, considerable rig time was saved. This paper discusses key aspects of the performance of the water-based, hydrocarbon-free, non-damaging lubricant used in drilling the Orinoco Oil Belt horizontal and multilateral wells, as well as the factors that enabled PDVSA to achieve project targets in a safe and timely manner and to minimize any detrimental environmental impact. Introduction Excessive rotating torque and axial forces (drag) on drillpipe can account for significants portions of the hookload when the drillstring is moved in a directional well. Parameters affecting torque and drag are well trajectory, drilling fluid, pipe geometry, coefficient of friction (for both cased and open hole), and borehole conditions. One of the most important of these factors is coefficient of friction (COF). COF results from wellbore and drillstring interaction in the open hole and is a complex process that is affected by temperature, pressure, properties of contacting surfaces, their geometries and contact loads in the presence of drilling fluids and filter cakes. During the process of drilling a directional well, frictional forces that occur between the drillstring and the wellbore or casing can cause a variety of severe problems, including stuck pipe incidents. High torque and drag can exceed the capabilities of the drilling equipment and limit horizontal displacement of the hole. When drilling highly deviated sections, high friction forces between the drillstring and the borehole wall can increase the torque and power required to rotate the drillpipe and the stress on the pipe.