Characterization and Control of Fine Particles Involved in Drilling
Authors: Mohnot S.M. 
Published: December 2007

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An automated particle size analyzer was successfully used in the laboratory, as well as in the field, for characterizing fine particles involved in drilling. Particle size distribution data particles involved in drilling. Particle size distribution data were obtained on weighting materials, clays and field mud samples in the range of a fraction of one to 192. Size analysis is a useful quality control tool to limit undesirable size fractions (e.g. less than 2 and greater than 74 ) in weighting materials. The median size measured for clay systems are found to represent the flocculation state of the clays in various salt environments. The measured size distributions of the solids in fresh unweighted water-based field muds are shown to be a good indicator of the operation of the solids removal equipment. The separation efficiencies of the 4" hydrocyclones were calculated from which the median separation size was found to be around 35 . An indication of the nature of the formation drilled was evident from the data.

Introduction

It is now commonly recognized in the oil industry that the solid particles involved in drilling have an immense influence on the economic and technical success of drilling and oil production. These particles are either added at the surface to prepare the mud, e.g., via weighting materials and clays or produced from drilling the formation. The understanding of the physical characteristics (size, shape and hardness) and chemical characteristics (surface charged nature) of these particles in the drilling fluid environment is crucial to the development of drilling fluid technology. The behavior of these solid particles in mud systems is manifested through differential pressure pipe sticking, clay/shale stability, dependence of rheology and penetration rate on solids, and efficient control of solids by certain solids removal equipment.

Numerous papers and reports have been written since the late 1950's addressing adverse effects and the need for proper control of solids, solids analysis and performance of solids removal equipment. A few are listed in references. However, most of the results of the influences of solid particles are very qualitative or highly empirical. The understanding of drilling fluid systems can only advance by applying the knowledge of Particulate Technology and Colloid Science. Recently, Lauzon applied the techniques of Colloid Chemistry to characterize the chemical surface nature of drilling fluid solids. More recently, Roehl applied the concepts of Clay Colloid Chemistry to explain his experiments leading to a better understanding of shale stability. Complimentary to these, the industry needed a suitable technique to measure particle size distribution. The techniques used in the past were either very slow well suited to most drilling applications.

This paper reports the extensive search undertaken to evaluate commercially available instruments to measure the particle size distribution of drilling fluid solids both for research and field use. Based on this evaluation, a laser diffraction device was purchased and tested both in the laboratory and the field. The purchased and tested both in the laboratory and the field. The particle size distributions in commercial weighting agents, clay particle size distributions in commercial weighting agents, clay suspensions and field drilling muds have been measured. From the field test data, separation performance of the solids removal equipment was evaluated.

PARTICLE SIZE ANALYZER PARTICLE SIZE ANALYZERAn automated and portable French particle size analyzer was used in this study. The instrument is based on laser diffraction and it measures the size distribution of particles from a fraction of one to 192 p. This instrument would be referred to as the "Particle Size Analyzer" in this paper. The details of comparison of particle size analyzers and the results of analysis by those are provided in Appendix A. provided in Appendix A. In using the particle size analyzer, dilute suspension (500 m of the sample is made in a suitable medium (generally water). The suspension is agitated and continuously circulated through the measurement cell.

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