A Unique System For Preparation And Evaluation Of High-Temperature Drilling Fluids
Authors: Wyant Reece 
Published: December 2007

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.

Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

Successful drilling of deep oil wells critically depends on drill fluids designed for specific down hole conditions. A new dynamic time-and-money saving circulation system stabilizes and tests high-temperature drilling fluids more accurately and reliably than previously possible. In this new system, a volume of mud is repeatedly pumped from an atmospheric pressure reservoir through a cycle of heating, high temperature shearing, cooling, low temperature shearing, and finally is returned to the reservoir. The system, which provides a laboratory mud equivalent to a mud produced in a deep high-temperature well over a prolonged time, is here described and contrasted with conventional test systems.

Introduction

Very few laboratories presently can formulate and test stable high-temperature drilling fluids in less than one to three weeks. This paper describes a compact new circulation system which significantly reduces preparation and evaluation time to a maximum of 48 hours and, for moderate temperature and shear fluids, a minimum of approximately 15 hours.

The savings in time, money and manpower are obvious to engineers, drilling managers, and laboratory personnel accustomed to waiting out the tedious weeks required for conventional bomb methods. Moreover, comparisons with conventional methods indicate two further superior features of this new circulation system: mud and mud components stabilize more completely; and laboratory muds thus produced more accurately represent good field muds produced after extended high temperature drilling.

For those of us whose livelihoods depend on our ability to provide superior research services, our essential task is to provide superior research services, our essential task is to provide quickly and efficiently the best possible drilling fluid provide quickly and efficiently the best possible drilling fluid materials for ever-deeper wells drilled in different parts of the world under widely differing conditions. Clearly, we must strive to anticipate actual drilling conditions, and to develop and test materials to withstand those conditions. The testing problems multiply by leaps and bounds as well temperatures problems multiply by leaps and bounds as well temperatures increase, and we all face the perennial problem: How to quickly obtain and test drilling mud in the laboratory which accurately simulates the muds produced during field drilling?

Conventional laboratory stabilization methods generally involve high temperature aging of mud in small rotating pressure cells, or bombs, where frequent cooling, stirring, treating, cell resealing, and reheating provide continued aging. To yield sufficient amounts of good stable mud for high temperature tests, those procedures demand many cells and samples, and one or two weeks of daily treatment. Moreover, regular mud property analysis is feasible only when aging is interrupted. property analysis is feasible only when aging is interrupted. Since bomb methods require extensive manipulation, laboratory procedures are often simplified to save time. The problem with short cuts is that erroneous test data may result from continued changes in unstable clay systems which alter the actions of treating chemicals.

To test muds more correctly without use of inadequate bomb methods, other circulation systems have been designed. These include those developed by Kelly and Hawk (a large, automated, closely controlled system in which previously stabilized muds can be tested precisely) and de Lautrec (known as the Mud Link, and used for detailed mud testing at well bore temperatures and pressures).