Mud Displacement During Cementing State of the Art
Authors: Sauer C.W. 
Published: December 2007

Distinguished Author Series articles are general, descriptiverepresentations that summarize the state of the art in an area of technology bydescribing recent developments for readers who are not specialists in thetopics discussed. Written by individuals recognized as experts in the area, these articles provide key references to more definitive work and presentspecific details only to illustrate the technology. Purpose: to informthe general readership of recent advances in various areas of petroleumengineering.

This paper is a summary of past and present work on the subject ofmud displacement during cementing. Such topics as centralization, pipemovement, pipe-lowering speed, drilling-fluid conditioning, hole geometry, spacer design, flow rate, equivalent circulating density, job monitoring. postjob evaluation. and the application of each to the mud-displacement postjobevaluation. and the application of each to the mud-displacement process arediscussed. This work includes a mud-displacement "checklist" process arediscussed. This work includes a mud-displacement "checklist" for use before andduring cementing. Although most of what is discussed has been presentedpreviously, this discussion will tic all these critical points into onediscussion for use by both operations and engineering points into onediscussion for use by both operations and engineering personnel involved incementing jobs, personnel involved in cementing jobs.

Introduction

The replacement of drilling fluids with cement to support and to protectcasing, as well as to seal formation pressures hydraulically, has been thedesire of prudent operators for 75 years and is at a point where well-definedmechanics of mud displacement are understood. Personnel and environmentalsafety, the success of an exploration program, the validity of reservoirengineering calculations, and good placement control of stimulation treatmentsdepend on placement control of stimulation treatments depend on well-cementedcasing, yet there are still many instances of poor placement design incementing operations.

The cementing of an oil, gas, or injection well can be one of the mostdifficult tasks encountered during the drilling or completion of the well if itis done correctly. Unfortunately, at least one cementing operation is performedon every well drilled, so the cementing is often thought of as routine and maynot get the proper attention. Because it is seldom required to prove thequality of the cement job, and even when it is, evaluation tools and methodscan be less than perfect, many cement placement mistakes are never discovered. if enough subsequent production tests show communication with zones other thanthose desired, it may be believed that a good cement job is impossible toobtain.

But a good cement job is possible. It takes a considerable effort by allconcerned: the drilling foreman, drilling engineer, drilling contractor, andvarious service companies involved. The planning must take place days, weeks, or sometimes months before drilling. To replace the mud used to drill the hole, to cement, and to form a hydraulic seal properly, efforts will have to be takenduring drilling, properly, efforts will have to be taken during drilling, logging, casing running, precirculation, cement mixing, displacement, plugbumping and waiting-oncement time.

It should not be believed that the cement job will be easy. regardless ofwhat else is taking or has taken place during drilling to the casing point. Hole place during drilling to the casing point. Hole geometry, mud viscosity, pipe running speed, centering of the casing, mud type, mud/cementcompatibility, displacement flow regimes, and many more aspects of the totaloperation must be considered. No single additive, technique, or magic will makecementing a success. A complete engineering analysis of all the parameters inthe cementing equation must be undertaken to guarantee success.

With this in mind, this report will investigate the state of the art of muddisplacement during cementing. Although oil-based muds are used on a regularbasis in some areas of the world, the greatest amount of work reported on muddisplacement has been with water-based muds. Still, it is believed that most ofthe basics apply regardless of the type of mud in the hole.

P. 1091