Study And Application On The Laws Of Hydrofractured Cracks Propagation In Tight Sandstone Reservoirs

Hydraulic fracturing is a necessary means to realize the efficient development of tight oil and gas reservoirs.The effect of oil and gas reservoirs after fracturing mainly depends on whether the fracturing fractures can effectively communicate with the target oil and gas area,provide sufficient conductivity and establish sufficient space transformation system.However,the development effect of tight oil and gas reservoirs in China is not consistently satisfactory at present,and it is necessary to futher study the fracture propagation mechanism of hydraulic fracturing in tight sandstone.Aiming at the tight sandstone outcrop of Shahezi Formation,this paper carried out the physical simulation experiment of true triaxial hydraulic fracturing,studies the influence of natural fracture(NF)development degree,in-situ stress condition,fracturing operation parameters,temporary plugging thchnology and other aspects on the degree of reservoir fracturing,and the model of fracture propagation based on hydro-mechanical-damage coupling was established,numerical simulation is used to simulate the fracture propagation and reveal the fracture propagation law of hydraulic fracturing in tight sandstone reservoir.NF is a key factor to determine the hydraulic fracture(HF)morphology in the tight sandstone reservoir.Further,the number of primary natural fractures,approaching angle and cementation strength of the preexisting NF affect the HF propagation path of hydraulic fractures;these are the main controlling factors for the formation of complex fractures.For tight sandstone reservoirs with well-developed NFs,the final fracture morphology is mainly affected by the occurrence of NF when the horizontal principal stress difference is less than 9 MPa.When the horizontal principal stress difference is more than 12 MPa,it is less affected by natural fractures and easy to form a single fracture.In the fracturing at variable injection rates,a low rate facilitates fluid penetration into NF,while a high rate facilitates deep HF propagation.A lowviscosity fracturing fluid at a high rate facilitates further propagation of the temporary plugging agent,thus achieving deep temporary plugging and fracture diversion.A high-viscosity fluid does not facilitate accumulation and plugging of particulate temporary plugging agent.Higher horizontal differential stress leads to a smaller diversion radius of new HF,which is closer to the original HF,leading to poorer stimulation effect.When there is an angle between the initial fracture initiation direction and the maximum horizontal in-situ stress direction,the fracture will turn and expand and finally extend along the maximum horizontal in-situ stress direction.Higher the horizontal differential stress leads to a more serious the fracture direction changes near the well at the same initial fracture initiation direction.The results provide a reference for the fracturing design of the tight sandstone.