Factors Contributory to Bulk Handling Problems in the Offshore Oil Industry
Authors: Haynes A.P. 
Published: December 2007

Haynes, A.P., Member SPE-AIME, Burmah Oil Trading Ltd.

The accelerating increase in the cost of powdered materials used by the offshore oil industry, particularly barite, means that the loss of material in transfer operations both onshore and offshore is becoming increasingly significant. This paper reviews factors that influence bulk handling of powdered materials, both from a practical and theoretical view point, and makes some suggestions as to how present handling methods and specifications may be optimised.

Most of the losses can be related to the small size particle fraction of the materials (less than 5 microns) which travel at high velocities and remain entrained in the conveying air. Information from outside the oil industry has been used to study the optimum design of bulk handling facilities, and the operation is described from quay-side to rig or platform. A better understanding of the mechanics of bulk handling should permit not only an improved design of future systems, but also more efficient operation of present systems.

Introduction

The project was initiated in order to determine the reasons for losses of material during bulk handling operations in the North Sea region. This involved investigating if material specifications are adequate for bulk handling purposes. A loss of 20%-25% of barites at US $102.25 per metric ton represents about US $2000 per off-loading. It was found that the barites losses were greater than those of other materials such as bentonite and cement. Actual losses seen by the author while working on this project varied from 6% - 30%.

The scope of the research included the differing nature of the materials, loading techniques and storage installations. It was found that the relatively high air volumes and pressures required to convey finer ground and heavier barites also caused the smaller particles (less than 5 microns) to become entrained in the air flow and then pass straight through the vent system. If the pressure for conveyance is further increased by sharp bends or changes in pipe diameter, this entrainment effect is pipe diameter, this entrainment effect is accentuated. Operational efficiency is then reduced by slower transfer rates and increased losses of material. The examination of many systems showed that they are frequently substandard for maximum handling efficiency. The experience of bulk plant operators throughout all types of industry has proved that fast transfer rates cannot be obtained without having a minimum bend radius of 10–15 times the pipe's diameter. Yet generally much smaller radii bends are used in the oil industry with the result that most operations take place using receiving silos which are under a pressure which is higher than necessary, so increasing the vent losses.

THE ELEMENTS OF THE SYSTEM

During the last 20 years the most economic method of moving powdered bulk materials has been by pneumatic handling techniques. As the volume pneumatic handling techniques. As the volume and desired speed of transfer increases the benefits of having the material in bulk become obvious especially with respect to offshore operations. The more widespread use of this type of equipment has introduced design limits upon the system which need further investigation.