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| NUMERICAL SIMULATION STUDY OF HYDRAULIC FRACTURE INITIATION FOR PERFORATED HORIZONTAL WELL IN SHALE PLAY |
| GUO Tiankui1，ZHANG Shicheng2，PAN Linhua3 |
| (1. School of Petroleum Engineering，China University of Petroleum，Qingdao，Shandong 266580，China；2. School of Petroleum Engineering，China University of Petroleum，Beijing 102249，China；3. Chongqing Institute of Geology and Mineral Resources，Chongqing 400042，China) |
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Abstract To understand hydraulic fracture initiation mechanism of perforated horizontal well in shale play，the fracture initiation models of a 3D single-stage three clusters perforation and a single cluster perforation (containing natural fracture) were established by using Abaqus finite element calculation software. The effects of crustal stress，wellbore orientation，perforation parameters and natural fracture on fracture initiation pressure and location was studied. The results show that the initiation pressure of open hole perforation is far below that of the casing perforation. The fracture initiation pressure increases with the increasing of the minimum horizontal stress，but the influence degree is controlled by the ratio of vertical stress to the minimum stress. The effects of the maximum horizontal stress and vertical stress on the initiation pressure is very weak. The initiation pressure decreases roughly with the wellbore azimuth increases，when the natural fracture is presented，the initiation pressure does not show any linear law. The shear slip for natural fracture easily appears in the shear stress zone. Initiation pressure firstly decreases and then increases with the perforation azimuth increases. The change of perforation azimuth can seriously affect the fracture initiation morphology. The fracture initiation location is closely related to the minimum and maximum horizontal stress，wellbore azimuth and the cementing strength and azimuth of natural fractures. The internal perforations bear the additional stress along the wellbore direction generated by both sides of the perforations，the closure stress is increased，thus these perforations initiate more difficult，resulting in that fracture initiation sequence is from the endmost perforations to the middle perforations. When the stress difference is higher(＞7 MPa)，the additional stress interference becomes significant. To achieve a multi-fractures initiation from multi-perforations，the injection pressure needs to be improved. The change of initiation location in perforation tunnel is a competitive result between the strength of stress concentration on perforation root and the interference degree of additional stress on the distal end of perforation. Due to the great perforation cluster spacing，the effect of stress interference between perforation clusters on fracture initiation is very weak，the pressure distributions of every perforation cluster are almost identical.
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2015, Vol. 34 
