Abstract

A study using field and laboratory measurements to predict sand production for a multi-field gas development in offshore Peninsular Malaysia was carriedout. Formation depths ranged from 1225 to 2450 metres with most of these field shaving high CO2 and H2S content. Laboratory-derived properties were correlated with the openhole logs while 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 sand production prediction model was calibrated against laboratory perforation collapse tests. The effect of well inclination/orientation, perforation orientation, reservoir pressure depletion and water-cut on sand production potential was evaluated. As downhole sand control increases well cost significantly and impairs well productivity, an assessment of the likelihood of sand production to decide if sand control is necessary and the timing of installation becomes very critical.

Sand production was found to be not a problem in the early part of the production of the fields with high reservoir pressures and low water-cut. Two over-pressured formations may have sand production problem with declining reservoir pressures. Based on the results of the study and expected reservoir pressures, draw down and water-cut behavior of the fields, downhole sand control will not be required in the early stage of production.

This paper described the work done, techniques used, impact of the results of the study on the field development and benefits gained from the study.

Introduction

As part of a program to optimise the sand control strategy for the field development of a multi-field gas development, a sand production prediction study was carried out. The development consists of four gas fields with varying volumes of gas in place with the objectives of developing them as a group to optimise development cost and achieve economy of scale. Depths of the formations of interest ranged from 1225 to 2450 metres below mean sea level. Details of the fields in relation to sand production prediction parameters are given in Table 1. Figure 1 shows the location of the fields which are about 176km offshore Peninsular Malaysia.

Sand production is a natural consequence of fluid flow into a wellbore fromthe reservoir. The process may be divided into three stages, i.e. the loss of mechanical integrity of the rocks surrounding an openhole or perforation(cavity), separation of solid particles from the rocks due to hydrodynamic force and transportation of the particles to the surface by reservoir fluids. The key to sand production in weakly-consolidated and consolidated formations is the loss of mechanical integrity of the rocks surrounding the cavity.

This paper presents a study on potential of sand production in the multi-field gas development. Sand production from these fields is a concern for the development as unnecessary downhole sand control not only increases well cost significantly but also impairs well productivity. However, if no sand control is installed, sudden influx of large amount of sands into the wells will damage 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 work process of the study is shown in Figure 2.

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