Differential-Sticking Mechanisms and a Simple Wellsite Test for Monitoring and Optimizing Drilling Mud Properties

Abstract

Summary Differential sticking has a major impact on drilling efficiency and well costs. It is known to be influenced by drilling-fluid properties and other parameters, such as the characteristics of rock formations. Mechanisms of differential sticking were investigated using laboratory data and information in the literature. The knowledge gained was used to design a simple and robust device for measuring the sticking properties of drilling fluids, both in the laboratory, or at the well site. This device comprises a half-area high-pressure, high-temperature (HPHT) fluid-loss cell, modified to allow a metal sphere to be placed in contact with a growing mud filter cake. The torque required to rotate the sphere free from the mud cake is determined using an electronic torque gauge. A plot of torque against the 3/4 power of time gives a linear fit to the data. The slope of this line is indicative of the sticking potential of the mud. Laboratory and field data indicate that the test gives a good indication of mud condition and allows the user to investigate various options for reducing the sticking potential of the fluid. This information is useful both in the initial selection of mud type and in making technical and economic analyses of various mud treatment options. In addition to the laboratory evaluation described above, the sticking device has been used in several well-site tests with encouraging results. Some of these are described.