Field Study of Offshore Cement-Spacer Mixing

Abstract

Summary Rheological data from cementing-spacer fluids are usually based on laboratory-prepared samples of the spacer and used to determine the flow rate required to provide the flow regime necessary for maximum efficiency of the spacer and to estimate the annular friction pressures associated with the spacer. Actual rheological properties are rarely measured on location, and the problems experienced with settling, foaming, and mixing are difficult to simulate in the laboratory. This paper reviews the field data from three commercial spacers mixed at offshore locations and compares them with laboratory data for base spacer materials and weighted spacer mixes. The flow rates required to obtain turbulent and plug flow for each spacer are compared, and settling, foaming, and mixing problems are discussed. Because of solids settling in either the slugging pits or surface samples, the spacer formula is sometimes modified on location to improve solids suspension. The rheological effects of increasing concentrations of base spacer material, bentonite, and polyanionic cellulose (PAC) are discussed with a comparison of the rheological data from these spacers.