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Publisher Society of Petroleum Engineers Language English

Document ID 73768-MS DOI 10.2118/73768-MS

Content Type Conference Paper

Title Role of Starch in Designing Nondamaging Completion and Drilling Fluids

Authors Hylke Simonides, Gerhard Schuringa, AVEBE; Ali Ghalambor, U. of Louisiana at Lafayette

Source International Symposium and Exhibition on Formation Damage Control, 20-21 February 2002,

Lafayette, Louisiana

ISBN 978-1-55563-941-9

Copyright Copyright 2002, Society of Petroleum Engineers Inc.

Preview Abstract

Starch is a polymer that is widely used in all types of water based drilling fluids. With the development

of specialty drilling and completion technologies, starch is also chosen as one of the main components

of drill-in fluids. This paper presents laboratory results obtained from experimental work on chemically

modified potato starch. The results show, that properties like heat and shear resistance can be

improved by chemical modification.

The main functions of starch are fluid loss reduction and rheology control. In drilling fluids the polymer

interacts with solid particles to enhance the seal of the filtercake on the wellbore, and to provide therequired rheology. Reasons for choosing starch are its versatility, and compared to many biopolymers,

its relative low cost. During drilling operations the fluid rheology has to be controlled over a large

temperature interval. Like many polymers, starches tend to degrade at high temperature. The

degradation will lead to increased fluid loss and changes of the fluid viscosity, which can result in fluid

failure and lead to formation damage. It is well known that one of the factors affecting the

thermostability of a drilling fluid is the composition of the drilling fluid. Another factor is the nature and

the chemical modification of the starch. The starch has been modified by cross-linking and

carboxymethylation in order to improve the properties in drilling fluids at ambient and elevated

temperature.

Fluid properties such as fluid loss and viscosity will be presented as a function of the level of cross-

linking. The results indicate that high molecular weight starch exhibits the best fluid loss controlcombined with a shear thinning rheology, but there is an optimum for both when increase of the

molecular weight is obtained by crosslinking. Crosslinking does positively affect the heat stability. The

effects of substitution and cross-linking on the resistance to heat and pH are discussed for several fluid

compositions. The fluids have been aged at elevated temperatures under dynamic conditions.

A new heating apparatus was developed to perform these tests. This apparatus consists of a bath

equipped with a mechanical device to rotate fluid containers, like in the traditional hot air roller ovens.

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The bath is filled with silicon oil, which is circulated, rendering a homogeneous temperature profile.

The dynamic aging results thus obtained have proven to be more reliable than those obtained with

conventional hot air ovens. A detailed description of the new apparatus will also be presented.

Introduction

Non-damaging drilling and completion fluids have gained considerable interest during the last decades

because high angle well, multilateral and slim-hole technologies require fluids with special properties.

Deviated drilling operations need shear-thinning fluids with a good carrying capacity. Efficient clean-up

ability of drilling fluids is important in reservoirs for maximizing the well productivity. The changes in

drilling fluid rheology have shifted the requirements for the drilling fluid components. One of these

components is starch.

The requirements for drill-in starches are quite different from those of the traditional starch based fluid

loss reducing agents. The latter were designed to control filtration without contributing to the drilling

fluid viscosity. Developments in the composition of fluids for drill-in and completion purposes led to an

increased interest in starches that combined filtration-controlling properties with shear thinning

properties and contributions to the low-end shear viscosity. It was found that in particular crosslinked

starches were suitable for these purposes. Temperature restrictions of the current systems created

demands for products with improved resistance to heat and shear.