Abstract

The success of unconventional reservoir development relies on the technology of multistage hydraulic fracturing in horizontal wells. In each stage, multiple perforation clusters are often used to create multiple fractures to provide adequate drainage along the entire horizontal well and, at the same time, to achieve economic goals. However, the production contribution from each perforation cluster has been found to be highly uneven. One of the reasons for low cluster efficiency is that effective fractures are not created from all the perforation clusters. Field observations have shown that the magnitude of fracture breakdown pressure can vary significantly along a horizontal wellbore. Both the magnitude and the variation of fracture breakdown pressure can cause ineffective fractures and low cluster efficiency. A computer hydraulic fracture simulator was used to study the breakdown of multiple fractures from a horizontal well. The measured breakdown pressures from actual fracturing treatments in a horizontal well are used in the simulation. The simulation results show that only a limited number of fractures can be generated for a given pump rate, independent of the number of the clusters available in a stage. The number of fractured clusters depends on the magnitude and variation of fracture breakdown pressure. The simulator has also been used to show cluster efficiency can be improved by perforation designs, as well as by advanced diversion techniques.

1. INTRODUCTION

The success of unconventional reservoir development relies on the technology of multistage hydraulic fracturing in horizontal wells. In each stage, multiple perforation clusters are often used to create multiple fractures to provide adequate drainage along the entire horizontal wellbore. However, the production contribution from each perforation cluster has been found to be highly uneven, with 40% of the perforation clusters contributing little to no production [1, 2]. In recent years, engineered staging completions based on rock properties and log data along the horizontal wellbore have been used to improve the cluster efficiency with some degree of success [3, 4].

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