ABSTRACT:

This paper presents a study on the potential of sand production for an offshore multi-field gas development. Mechanical properties of the reservoir sandstones were established by conducting rock mechanics tests on reservoir cores. The laboratory measured mechanical properties were then correlated with the properties derived from openhole logs. The magnitudes of the in-situ stresses and formation pressure were derived from analysis of openhole logs, standard leak-off test data, coefficient of active earth pressure and qualitative stress information relating to the in-situ stress regime. The likelihood of sand production was assessed by analyzing perforation stability for cased, cemented and perforated wells. The sand production prediction model was calibrated against laboratory perforation collapse test data on full-size reservoir sandstone core samples. The effect of well inclination/orientation, perforation orientation, reservoir pressure depletion and water-cut on sand production potential was evaluated. The study shows that sand production is unlikely in the early stage of production for all the fields. However, sand production is likely to occur in some reservoir formations when the reservoir is significantly depleted (say by 50%). Furthermore, water-cut can increase the likelihood of sand production significantly.

1. INTRODUCTION

Sand production is a natural consequence of fluid flow into a wellbore from the reservoir [1]. The process may be divided into the following stages - the loss of mechanical integrity of the rocks surrounding an openhole or perforation (failure), separation of solid particles from the rocks due to hydrodynamic force (post-failure) and transportation of the particles to the surface by reservoir fluids (transport). The essential condition for sand production in weakly-consolidated and consolidated formations is therefore the failure the rock surrounding the cavity.

This paper presents a study on potential of sand production for a multi-field gas development located offshore Peninsular Malaysia. Sand production from these fields has been a concern for the development. On the one hand, unnecessary downhole sand control not only significantly increases well cost but also impairs well productivity; on the other hand, sudden influx of large amount of sands into the wells damages downhole and surface production equipment and can be a major safety risk. It is therefore critical to accurately assess the likelihood of sand production to decide if downhole sand control is necessary during production life of the multi-fields prior to the development.

The data required for the study were obtained from laboratory and field measurements. Mechanical properties of the reservoir sandstones were established by conducting a number of unconfined compressive strength and triaxial tests on reservoir cores in conjunction with ultrasonic wave velocity measurements. The laboratory measured mechanical properties were then correlated with the properties derived from openhole logs. The magnitudes of the in-situ stresses and formation pressure were derived from analysis of openhole logs, standard leak-off test data, coefficient of active earth pressure and qualitative stress information relating to the in-situ stress regime. The likelihood of sand production was assessed by analyzing perforation stability for cased, cemented and perforated wells. The sand production prediction model was calibrated against laboratory perforation collapse test data on full-size reservoir sandstone core samples.

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