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Abstract

The infiltration of fine particles into the reservoir and the resulting production decline has long been a problem to the petroleum industry. It is also generally accepted that petroleum industry. It is also generally accepted that formation damage due to particle plugging is not thoroughly understood. In contributing to the solution of this problem, an experimental study of more than 17 core plugs involving 25 linear runs has been conducted. The purpose was to study the different physical and mechanical aspects of the processes leading to formation damage caused by movement and entrap ment of suspended particles (when chemical and other forces are minimized).

Permeability is a key parameter among several others that control reservoir performance. The experiments are based on the results of permeability decline in linear core tests.

Two methods of flood tests; constant flow rate and constant pressure drop, were used on Berea sandstone. Plastic particles pressure drop, were used on Berea sandstone. Plastic particles were injected with ultra pure water as the transport medium. Essential filtercake properties required for the decline rate calculations were obtained.

Finally, particle characterization using the Coulter counter was analysed. The results combined with that of the filtercake properties were used to determine the mechanisms and extent properties were used to determine the mechanisms and extent of plugging.

Introduction

Movement of fine particles in reservoirs have long been recognized to cause formation damage. These fine particles could have been incorporated in the formation during geological deposition or can be introduced into the formation during drilling and production operations. production operations. Investigations and diagnosis of specific problems indicate that the reasons are usually associated with either the physical movement of fine particles, chemical reactions or a combination of both.

Stimulation chemistry, salinity shocks, temperature effects, pH, reaction of gases (CO2, H2S) etc. are all other important pH, reaction of gases (CO2, H2S) etc. are all other important aspects of formation damage. Further information on causes of formation damage may be obtained from Kreuger (1986).

In addition, formation damage may occur from fine particles introduced into the injection water. This particular cue is the subject matter of the present study. We have decided to hold constant every other variable causing the damage, while the effect of added particle is observed.

Formation damage caused by suspended particles has been, and continues to be a concept that is being accepted or rejected on the basis of personal opinion, experiences and perceived understanding of the process of producing oil and gas, Porter (1989). It can occur at any time during a well's history, recognized by lower-than-expected productivity or accelerated production decline on affected wells. production decline on affected wells. In a water flooding project there exists the risk that suspended particles in the injection fluid will cause injection wells to become impaired. The degree of impairment over a period of time is believed to be related to the total quantity of particles in the injection fluid, the particle size distribution and the formation characteristics. These factors determine the nature of the impairment mechanism (the formation of internal or external filter cake) and filter cake properties.

Although there are many aspects of well impairment caused by these suspended particles, this work is directed specifically to the mechanical characterization of the impairment.

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