Abstract
Hydraulic fracture initiation and near wellbore propagation is governed by complex failure mechanisms, especially in cased perforated wellbores. Various parameters affect such mechanisms, including fracturing fluid viscosity and injection rate. In this study, 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 the fracturing mechanisms. Hydraulic fracturing tests were conducted in cased perforated boreholes made in tight 150 mm synthetic cubic 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. The results indicated that by increasing the fracturing fluid viscosity and injection rate, the fracturing energy increased, and consequently, higher fracturing pressures were observed. However, when the fracturing energy was transferred to a borehole at a faster rate, the fracture initiation angle also increased. This resulted in more curved fracture planes. Accordingly, a new parameter, called fracturing power, was introduced to relate fracture geometry to fluid viscosity and injection rate. Furthermore, it was observed that the presence of casing in the wellbore impacted the stress distribution around the casing in such a way that the fracture propagation deviated from the wellbore vicinity.
Highlights
Hydraulic fracturing is commonly used as the most viable stimulation technique to improve the production rate and recovery factor of oil and gas reservoirs, especially in unconventional reservoirs.When performing a hydraulic fracturing operation in a cased perforated wellbore many problems may arise
The quality of a hydraulic fracturing operation could be negatively impacted by these issues, and the fracturing treatment may not improve the production of the wellbore effectively
The tests involved the use of three different fracturing fluids and a range of injection rates from 0.05 cc/min to 5 cc/min
Summary
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 would result in significant increase in the operation pressures and eventually premature screen-out [1,2,3]. 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]. 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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