New Lab Tests and Models Improve Planning for Complex Cementing Jobs Offshore New Zealand

Abstract

Recent investigative work for cementing highly deviated liners offshore New Zealand (NZ) employed several types of laboratory tests and numerical models-with many developed specifically for this project-to determine the best way to prepare the hole and then complete the cement job. Well-established test methods were used along with tests designed specifically to understand certain formation, mud, and cement interactions. The newly developed laboratory testing methods include: mud film testing using mud, spacer, and cement; ultra-low shear rheology (ULSR) testing under downhole conditions to determine mud and cement static gel strength development, as well as erodibility and removal of the mud by spacer and cement; Dynamic High Angle Sag Testing (DHAST) for both mud and spacer; and dewatering and filter cake build-up testing of mud, spacer, and cement, using a Fann 90 test apparatus. Both standard and newly-developed numerical models aided lab test data analysis in making decisions on materials and equipment and ensuring successful cement placement. One new model used DHAST data to check for effects on cement placement by calculating settled solids volumes dynamically deposited ahead of the cement slurry. A second model analyzed ULSR data to predict mud displacement results with different fluid properties designed for the mud, spacer, and cement. A third new model predicted displacement pressure effects by mud and cement interfacial mixing associated with certain cementing conditions and job procedures. The model also qualified the risk of multifluid vs. single fluid annular flow which determined procedures to minimize bypassed mud and cement slurry channeling. The results of these efforts greatly aided the understanding of the cement, mud, and spacer interactions with the formation. This paper aims to highlight the developed testing and modeling methods, provide information on the results of the methods, and demonstrate how the methods enabled the successful cementation of several highly deviated offshore liners in NZ.