Learnings from Foamed Cement Job Simulations
Authors: Guillot Dominique Jean , Le Bastard Eve 
Published: April 2012

Following the recent major incident in the Gulf of Mexico our industry isscrutinizing how foamed cement jobs are designed and executed. The objective ofthis paper is to highlight the benefits, which a foamed fluid placementsimulator brings to the design process. One example corresponding to ariserless section of a deepwater well illustrates this discussion.

The first part of the paper describes a compressible hydraulic model thatsimulates the flow of nitrified fluids during a primary cementing operation. Cement properties such as density, rheology and stability are affected by thefoam quality. While density changes can be determined quite easily, theevolution of rheology has not yet been fully characterized. The sensitivity ofthe critical simulator outputs to foam rheology are thereforeinvestigated.

The second part focuses on the evolution of foam quality as a function time. From the point where nitrogen is injected into the flow stream on surface toits final position in the well, foamed cement goes through a series ofpressurization, depressurization, and re-pressurization events. Using thesimulator, foam quality along the wellbore is analyzed during placement. Simulations show that foam quality close to surface can sometimes reach veryhigh values for a short period of time. It remains to be demonstrated whetherthe various foamed cement systems used in the industry today remain stableunder such extreme conditions.

The approach followed in this study provides a good base for safetycalculations of foamed cement jobs. Together with on-going laboratory studieson foam stability and foam rheology, this work will contribute to better andsafer foamed cementing operations.

Introduction

Foamed cementing has been presented as a cure all solution for primarycementing operations and even sometimes as a solution for remedial cementingoperations. Several advantages of foamed cement versus other non compressiblelow density systems have been reported but those are not always supported byundisputed scientific evidence. Nevertheless numerous shallow strings ofdeepwater wells have been cemented for years with foamed cement. Most of thetime these operations were successful thanks to key benefits of foamed cementi.e. some versatility in downhole density for a given composition of the cementblend and compressibility, which helps minimizing hydrostatic pressure loss inthe annulus after placement, therefore reducing the risk of fluid influx. Ofcourse these benefits remain effective as long as foam remains stable from thetime it is generated on surface until the foamed cement is set.

The objective of this paper is to demonstrate what information a dynamic foamplacement simulator can offer when evaluating foam stability. Such a simulatorcan show the evolution of foam quality from the point where nitrogen is mixedwith the base fluid till the end of the placement operation and even beyond. The first part of the paper describes the key features of the simulator usingan example of a riserless section from a typical deepwater well. The second andthird parts use this simulator to analyze the influence of fluid properties andwell conditions on the placement of this foamed cement.