Abstract

The successful application of fracturing for sand control has been reported from many different areas. Several explanations have been advocated for these successes such as "re-stressing" the wellbore, creation of a "halo effect" around the wellbore and maintaining the bottom hole pressure above a critical level to prevent perforation collapse. The latter approach has led to complex models predicting the conditions of perforation failure.

However, once the perforations have collapsed, the production of formation sand is governed by the transport of the sand from the perforation tunnels. Frequently, decreasing the production rate stops sand production, indicating that there is a critical flow rate below which sand cannot be transported into the wellbore. In this study, we present the development, application and field validation of a spreadsheet tool to improve the reliability of fracturing for sand control treatments.

A universal curve was generated from numerical simulations, showing that the percentage of the total flow through the perforations not connected to the fracture was a function of the formation and fracture properties and was independent of the reservoir fluid properties. The generation of a universal curve eliminates the need to use a reservoir simulator and allowed the development of a tool to aid the design of fracturing for sand control treatments. The spreadsheet tool has been validated with data from successful fracturing for sand control treatments.

Introduction

Successful applications of fracturing for sand control have been reported in the literature1,2 as well as in the field. Several mechanisms have been proposed for these successes. Some have put forward the "re-stressing" of the wellbore3 via the addition of a foreign material: the proppant pack. Some have investigated the creation of a "halo effect" around the wellbore4. Others studied the elevation of the bottom hole pressure to prevent perforation collapse.5 The latter approach led to the development of complex models predicting the conditions of perforation failure.6,7,8 In cases where optimised perforating (0° phased or 180° phased oriented in the preferred fracture direction) has been followed by fracturing, the fracture covers all the perforations eliminating problems due to failed perforations.1

In most of the field cases reported in which fracturing for sand control has been used, sand production had already begun. In the reported cases, sand production may have come from perforation debris or failed perforation tunnels.9 The quantification reported has never been sufficiently accurate to distinguish between these two cases. Nor do we have enough information to assess whether the sand production regime was transient (sand bursts) or permanent.3 In both cases however, we can conclude that the flow rate in at least one perforation was sufficient to produce enough sand to require a remedial operation. The importance of fluid flow in the perforations has been recognised by Tronvoll et al.8 to describe the sand production pattern after perforation collapse.

Interestingly enough, the flow rate at which sand production started is normally available from these wells. It is logical to interpret the flowrate at which sand production is detected as a critical flowrate below which no sand is being transported towards the wellbore - assuming that the flow rate is sufficient to lift the produced sand up the production tubing. In the present study, we analyse how fracturing affects the flow pattern in the near wellbore area, and how we can use fracturing alone as a sand control/sand management tool.

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