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Abstract

A series of laboratory flow experiments were conducted to examine the relative effects of various factors causing gradual losses in injectivities in fieldwide water injection operations. Injectivity losses were measured on a small scale during radial flow injection of carefully prepared particle suspensions with KCl as a base fluid.

Systematic matching of rocks mean pore sizes and the mean particle sizes in the suspension pointed out their effect and control on the mechanism of injectivity impairment.

Additional factors studied included the impact of prefiltration using microfilters and the role of differential pressure in enhancing the injectivities.

Introduction

Injectivity index is an important yardstick in the planning and operational aspects of fluid injection operations. Once a project is operational, it is desirable to project is operational, it is desirable to closely follow the injectivity losses if injectivity losses can be predicted, appropriate remedial actions may be taken to ensure continual pressure maintenance in a given flood and to prevent shallow and deep formation damage.

Among the approaches used in the past to predict injectivity indices, one may list predict injectivity indices, one may list theoretical models, step-rate tests and laboratory scale physical model tests. Theoretical approaches include various filtration models where the emphasis is on the rate and the properties of cake buildup against a permeable formation. Only in recent years emphasis is being focused on including the pressure losses due to fine migration and deep bed filtration. Because of the complicated nature of the interactions of various factors influencing fine invasion and migration, a universally applicable prediction model has not yet been proposed. Empirical observations and correlations are needed to elucidate the exact nature of the phenomena.

Step-rate-tests are a very useful tool for determining injectivity indices. These tests are, however, limited in their usefulness in predicting injectivity losses.

Remoteness of the sandface precludes the identification of the exact cause or causes of injectivity impairment. Permeability variations in a given strata further complicate the pinpointing of the troublesome intervals.

Whenever foreign waters are pumped into a well, whether as completion fluids or injection fluids, care must be taken to prevent formation damage. The quality of prevent formation damage. The quality of water with respect to its suspended solid content should be measured in the laboratory. This will aid in the design of proper filtration facilities and will prevent over or under designing of filters.

Doscher and Weber suggested the use of membrane filter tests.

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