Oil Base Spacer System for Use in Cementing Wells Containing Oil Base Drilling Muds
Authors: Morris E.F. , Motley H.R. 
Published: December 2007

This paper was prepared for the 48th Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Las Vegas, Nev., Sept. 30-Oct. 3, 1973. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made.
Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

Abstract
The incompatibility of a cement slurry and oil base mud mixture can be very severe to the point where an unpumpable mass may form. The point where an unpumpable mass may form. The presence of an oil base mud in a well to be presence of an oil base mud in a well to be cemented requires a spacer system to pump ahead of the cement slurry. Many types of spacers have been used with varying degrees of success. This paper describes the development and field application of a one-stage, oil base spacer system that is compatible with oil base muds or cement slurries and imparts compatibility to a mixture containing all three components. The spacer has a solvent action on oil base muds to improve mud removal and leaves surfaces contacted water wet. The density of the system may be varied as required. The system exhibits the desired effects under high temperature and pressure conditions. A number of field jobs have pressure conditions. A number of field jobs have been performed with excellent results.

Introduction
Drilling muds are normally present in an oil well at the time of cementing the necessary pipe strings. The accepted procedure is to pipe strings. The accepted procedure is to displace the drilling mud with the cement slurry. Drilling muds may be classified as water base or oil base systems. A broad definition of an oil base system is a mud where oil is the continuous phase and any water present is the dispersed phase. Oil base muds consist of two basic types:a water-in-oil emulsion referred to as an invert emulsion mud with the per cent water ranging up to 50 per cent by per cent water ranging up to 50 per cent by volume;an oil mud consisting of a hydrocarbon fluid and asphalt with very little if any water present.
The hydrocarbon fluid in either case is usually diesel oil or kerosene. Various additives and weighting materials are added to accomplish the desired drilling performance in a given well.
The possibility of comingling or mixing of a cement slurry and drilling mud downhole always exists during pumping and displacement. The incompatibility of an aqueous cement slurry and either type of oil base mud can be severe to the point where a mixture of the two forms an point where a mixture of the two forms an unpumpable mass. This results in failure to displace the mud and cement slurry to the desired position in the annulus. Cement may be left in position in the annulus. Cement may be left in the casing, tubing, or drill pipe requiring costly drilling out or result in even more serious problems.
The presence of oil base mud in a well to be cement normally requires a spacer system to pump ahead of the cement slurry. pump ahead of the cement slurry.