Scleroglucan Biopolymer Enhances WBM Performances
Authors: Gallino G. , Guarneri A. , Poli G. , Xiao L. 
Published: December 2007

Xanthan Gum is the most popular biopolymer used today to provide hole cleaning and suspension capabilities to water based drilling fluids but it presents some limitations as regards temperature sensitivity and tolerance to field contaminants.

In this paper a Scleroglucan is proposed as a better alternative to Xanthan Gum for drilling fluid compositions. Superior benefits offered by Scleroglucan on hole cleaning, rate of penetration, temperature sensitivity and mud tolerance to shale have been demonstrated by successful field applications and by extensive laboratory studies.

Introduction

Scleroglucan is a biopolymer produced by fermentation of a plant pathogen fungus of genus Sclerotium that has already found wide applications for enhanced oil recovery such as for polymer flooding and water shutoff.

Owing to its excellent suspending and viscosifying power, its high resistance to shear rate and its unique thermal stability it is presently considered one of the best mobility control agent in high salinity and high temperature reservoirs.

So far, only a few authors have considered the potential advantages of using Scleroglucan also for drilling applications.

In the patent literature Scleroglucan has been recently proposed for drilling fluids, spacers, and cement slurries.

The Scleroglucan non ionic nature and major thermal stability suggest that it should be able to perform better than Xanthan Gum for many drilling applications.

No published data have never been reported, however, regarding drilling applications of Scleroglucan.

By the authors the performances of Xanthan Gum and Scleroglucan based muds have been directly compared by drilling nearby wells with carefully designed formulations. Substitution of Xanthan Gum with Scleroglucan in a potassium based mud resulted in a reduction of dilution rates (-20%) and time spent in mud conditioning or bit balling (-60%).

Besides, improved mud rheology also contributed to the realization of much faster drilling rates through the water sensitive shales of the 12 1/4" section (+40%).

In this paper field observations are discussed and extended with the results of laboratory studies in which fundamental rheology plays a major role.

Rheological measurements are performed both in stationary and oscillatory fields.

Low shear rate viscosities at 0.06 sec and Herschel & Bulkley yield stresses are used to quantify hole cleaning capabilities and critical MBT of lab formulations and field muds.

Evaluation of cleaning efficiency and cutting concentration is performed with an in house developed program using the Walker and Mayes theory modified with the Herschel & Bulkley rheological approach.

The oscillation parameters Storage Modulus (G'), Loss Modulus (G") and Loss Tangent (G"/G') are used to characterize the "undisturbed" structure and thixotropy of the systems.

According to existing theories and to the results of the authors field experience and laboratory studies with analogous formulations, Loss Tangent and Storage Modulus are related to the degree of structuration and to the "strength" of the structure that develops in biopolymer solutions and muds under static conditions.

As a consequence, these data are analyzed to determine the suspension capability and resistance to shale contamination of the systems.

On the basis of field experience and laboratory studies the main advantages offered by Scleroglucan for drilling muds compositions are confirmed and underlined.

The reported field data refer to the first application of Scleroglucan in a Potassium Formate based mud.

In the same field other wells were drilled using Scleroglucan in different operative conditions and mud formulations and always with good results.

The discussion of these data will be reported elsewhere.

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