Abstract

In this study, hydraulic fracturing tests were conducted on 150 mm synthetic cubic samples. The borehole drilled in the center of the sample was cased and perforations were created in the samples. A true tri-axial stress cell was used to simulate real far field stress conditions. In addition, dimensional analyses were performed to correspond the results of lab experiments to field-scale operations. Three different fracturing fluids with viscosities ranging from 20 to 600 Pa.s were used to investigate the effects of varying fracturing fluid viscosities and fluid injection rates on fracturing mechanism. The results indicated that by increasing the fracturing fluid viscosity and fluid injection rates, the fracturing energy rises, and consequently the fracturing pressures will increase. However, as the fracturing energy is transferred to the sample at a faster rate, the fracturing power increases, and accordingly the fracture initiation angle rises; this would lead to more curved fracture planes. It was evident that fractures would reorient perpendicular to the minimum principal stress direction despite the angle of initiation. Furthermore, it was observed that the presence of casing in the wellbore would influence the stress distribution around the casing in such a way that the fracture propagation tends to deviate from the wellbore vicinity.

1. INTRODUCTION

Hydraulic fracturing is commonly used as the most viable stimulation technique in order to improve the production rate and recovery factor of the oil and gas reservoirs. When performing a hydraulic fracturing operation in a cased perforated wellbore many problems may arise. These problems lead to high frictional pressure losses near the wellbore, and consequently would result in significant increase in the operation pressures and eventually premature screen-out [1-3]. Additionally, other issues such as multiple fracturing and near wellbore fracture tortuosity have been encountered during the implication of the hydraulic fracturing operation in cased perforated completions [4]. The quality of a hydraulic fracturing operation could be negatively impacted by these issues, and consequently the fracturing treatment may not improve the production of the wellbore effectively. Such kind of challenges are mainly due to the existence of the perforations cavities which complicate the fracture initiation and near wellbore propagation [5, 6].

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