Effects of Cyclic Fracturing on Acoustic Events and Breakdown Pressure
- Abhishek Agrawal (University of Oklahoma) | Ahmad Sakhaee-Pour (University of Oklahoma)
- Document ID
- Unconventional Resources Technology Conference
- SPE/AAPG/SEG Unconventional Resources Technology Conference, 24-26 July, Austin, Texas, USA
- Publication Date
- Document Type
- Conference Paper
- 2017. Unconventional Resources Technology Conference
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- 128 since 2007
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In hydraulic fracturing, large volumes of fluid and sand are injected into the formation to enhance the transport properties. In conventional fracturing, the fluid pressure is increased monotonically to reach failure in a single cycle. The maximum pressure for the failure can be reduced if we increase and decrease the fluid pressure cyclically (cyclic fracturing). More acoustic events, which correspond to a larger enhancement in the stimulated region’s permeability, are recorded in cyclic fracturing. In the present study, we discuss the difference between the recorded events for the two methods. Four blocks of Tennessee sandstone were hydraulically fractured under triaxial stress: two under conventional loading and two under cyclic loading. We also use a modified Paris law to predict the breakdown pressure in cyclic fracturing, based on linear elastic fracture mechanics (LEFM), which treats the solid domain as an isotropic and linear elastic medium. We use the two conventional tests and one cyclic test to determine the unknown parameters in the modified Paris law. The tuned model, with determined parameters, can help us design an optimum scenario that is fundamentally different from the conventional method for formation stimulation. The results are promising and more lab measurements are required to test the accuracy of the developed model.
Hydraulic fracturing has become an essential part of the petroleum industry, as it enables us to produce hydrocarbon from tight formations by improving their transport properties. Most of the existing techniques are based on linear elastic fracture mechanics (LEFM); thus, that topic is briefly reviewed here.
Inglis (1913) started linear elastic fracture mechanics (LEFM) by analyzing the stress field around an elliptical crack in brittle materials. He proposed that the stress at the crack tip is proportional to the length of the major axis of the crack and the tensile load. Later, Griffith (1920) used the energy balance criterion to derive a relation for crack propagation. Irwin (1957) described the stress at the crack tip in terms of the stress intensity factor (SIF).
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