Frature Morphology And Propagation Mechanism Of Radial Well Fracturing In Sandstone Reservoir

Radial well fracturing is a reservoir stimulation technology which combines radial drilling and hydraulic fracturing.This technology can directly drill the radial well in the oil layer and fracturing,and has the characteristics of small scale,low cost and short operation time.Through decades of continuous innovation and improvement,this technology has achieved good stimulation effects in many oilfields all over the world.However,when some oil and gas wells use this technology,there are some problems,such as fracture midway diverting,unable to communicate with the target reservoir,and so on.Therefore,it is very important to clarify the fracture morphology and propagation mechanism of radial well fracturing to provide technical support for the large-scale application of this technology.Based on the data of a tight sandstone reservoir in Sichuan Province,considering the problem that fracture intersection cannot be simulated by conventional hydraulic fracturing numerical simulation,with the aid of triaxial stress hydraulic fracturing experiment,combining with hydraulic fracturing numerical model based on the voronoi mesh and finite discrete element,the influence mechanism and law of radial well azimuth angle,horizontal geostress difference,construction displacement,fracturing fluid viscosity,number and phase angle of radial wells on in-situ stress state and fracture propagation during radial well fracturing are systematically investigated and analyzed.The results of experiment and numerical simulation show that radial well can induce in-situ stress to some extent during radial well fracturing.When multiple radial wells exist at the same time,there is mutual interference between radial wells.The high stress area mainly concentrates in the near-well region.No matter how the construction conditions change,the crack always starts at the radial well root and propagates along the radial well direction for a certain distance.When the hydraulic crack extends to the far-well area,it will deflect to a certain angle toward the direction of the maximum horizontal principal stress.When unidirectional radial well fracturing is performed,the degree of crack deflection increases with the increase of azimuth and horizontal stress difference,decreases with the increase of construction displacement,first increases and then decreases with the increase of fracturing fluid viscosity.When multi-directional radial well fracturing is performed,more the number radial wells and smaller the phase angle,the area of induced stress and interference stress is larger,and the complex cracks are easier to created.When the phase angle is less than or equal to 60°,it is easy to generate branching fractures connecting two radial wells.When the phase angle is between 60° and 90°,the hydraulic cracks in the stress disturbance zone are irregular,but it is difficult to form branching cracks connecting two radial wells in the stress disturbance zone.When the phase angle increases to 120°,the direction of crack propagation is hardly disturbed by the interference stress.When the angles between the two radial wells and the maximum principal stress are different,the radial well with smaller angle will crack preferentially,and the degree of crack deflection is smaller,and the stress interference area is larger.The research result provides a reference for optimizing radial well fracturing of sandstone reservior,and is helpful to achieve rapid and efficient development of sandstone reservior.