Thickening Time Measure To Simulate Cementing Operations on Deepwater Wells: Field Laboratory Validation
Authors: Ramos R.C. 
Published: October 2008

A new laboratory procedure was developed and successfully used in the field in order to measure thickening time properties of cement slurries used in primary casing cementing jobs on deepwater wells.

Recommended lab testing procedures for cement slurries do not apply for this new physical environment. This paper presents a suggested method to estimate the bottomhole circulating temperature at the testing depth. The method uses an atmospheric pressure consistometer connected to a cooling system easily adapted at any field lab in order to reach the expected temperature. In this way, real well conditions were simulated.

INTRODUCTION

Adequate thickening times are required for a good cement job. Excessive waiting time will provide a weak support which can risk the well structure and severely damage the subsea head equipment.

A cement slurry's physical properties behavior at low temperature generally differs a lot compared with the same slurry system tested at surface temperature.3

These differences (table 1) can be 100% or more for the thickening time parameter, depending on slurry composition and density. The resulting increase in waiting-on-set cement time will also increase the final drilling cost.

From the compressive strength point of view4, the situation is worst for the low density slurries which usually develop a very weak structure when cured at this extremely low temperature.

This type of problem was first outlined when drilling companies started their development operations on the newly discovered giant fields of Marlin and Albacora located in Campos Basin-Southeast Brazil, having water depths varying from 400 m to 2,200 m and temperature as low as 40 ° F (fig. 1).

In order to simulate in the lab what is physically happening to the cement slurry, a cooling device was adapted to an atmospheric pressure consistometer (fig. 2) which kept the slurry at temperatures as low as 40° F throughout the test. The cooling device was made with a commercial condensation unit having an evaporator temperature above -18°F and electrical compressor of% HP capacity as shown on figure 3.

To define at what temperature the test must be run, a mathematical equation was deduced from thermic balance calculations done at a given water depth. Considering that this type of job always uses drillpipe and a stab-in tool very close to the casing shoe, it was defined and calculated that any cement slurry system will be in turbulent flow inside the drillpipe with the pump rates normally used. In this way the prevalent condition related to the heat transfer modeling point of view was established.

TEMPERATURE PREDICTION MODEL

In order to estimate the expected temperature for the pumped fluids at a determined pumping rate, pipe diameter, and well depth, it was necessary to make a few assumptions.Turbulent Flow is the predominant flow pattern for any fluid pumped from surface due to the reduced inside diameter of the drillpipe.No heating effect was considered because of the negligible influence of earth temperature gradient on the drillpipe temperature below sea bed level.