Primary Cementing: The Mud Displacement Process

Abstract

Abstract Various displacement factors which influence the primary cementing displacement process, other than primary cementing displacement process, other than pipe movement, were investigated using a large-scale pipe movement, were investigated using a large-scale apparatus that simulates actual field conditions. Results show that the condition of the drilling fluid is directly related to primary cementing success. Characteristics of the mud filter cake are dominant parameters affecting removal of the mud. Simply parameters affecting removal of the mud. Simply stated, if mud loses its fluidity, it becomes very difficult to displace. Results indicate that annular velocity is an important factor affecting displacement. High flow rates, whether or not the cement is in turbulent flow, provide better displacement than plug flow rates. Additional conclusions are stated governing cement rheology, density, centralization, and other displacement parameters. The relative importance of displacement parameters. The relative importance of displacement factors may be realized by considering the mud immobility factor defined in this report and the total flow energy of the cement. There appear to be two major opposing forces in cement/mud displacement, namely: a resisting force (the immobility of the drilling fluid) and a displacing force (the flow energy of the displacing fluid). Displacement may be improved by either decreasing the immobility of the drilling fluid by improving the mud properties, or by increasing the flow energy of the cement. Introduction Effective displacement of drilling fluid by cement is a critical factor in successful completion of oil and gas wells. Primary cementing failures are predominantly created by channels of drilling fluid predominantly created by channels of drilling fluid by-passed by the cement in the annulus. This paper will demonstrate that channels are highly dependent upon how the drilling fluid deposits a filter cake upon the permeable wellbore wall. A theoretical study could not adequately simulate the removal of or the thixotropic characteristics of the mud filter cake. Because of this, any theoretical study of the actual displacement process requires great. care in interpreting results. An experimental approach was adopted to determine the importance of various displacement factors in the primary cementing of a vertical wellbore. This paper identifies the importance of various factors under actual field conditions in the absence of pipe movement. Optimization of the displacement factors may then be realized to improve probability of obtaining a satisfactory primary probability of obtaining a satisfactory primary cement job. PRIOR INVESTIGATIONS PRIOR INVESTIGATIONS Research in displacement mechanics was first done by Jones and Berdine in 1940. From their work, and subsequent research, six basic factors which influence displacement in a vertical wellbore have been recognized, namely:–-condition of the drilling fluid–-pipe movement–-pipe centralization–-flow rate–-amount of fluids flowed past a particular interval–-difference in density between the two fluids. Howard and Clark first recognized the importance of the condition of drilling fluid. They concluded that a decrease in viscosity of the drilling fluid will increase displacement efficiency. McLean, Manry, and Whitaker also studied mud condition effects. They concluded that increasing gel strength increased the difficulty of displacing the drilling fluid. McLean, et al., went on to define a "critical yield strength" as a function of drilling fluid yield point and wellbore geometry. Minimizing this critical value, by lowering the yield point of the drilling fluid, would greatly improve point of the drilling fluid, would greatly improve the probability of successfully displacing the drilling fluid. McLean, Manry, and Whitakers performed an extensive study on how pipe movement affects the displacement process.