Study On Response Characteristics Of Hydraulic Fracturing Reservoir Stress Disturbance

Hydraulic fracturing is an essential technology for extracting unconventional natural gas.One hand,it injects excessive fluid into the reservoir pores than its elasticity can bear,to breakdown and open the reservoir formation.On another hand,due to the compatibility of deformation,stress disturbance will be generated since hydraulic fracturing volumetric opening,which means that additional stress will be generated over the far-field stress in the reservoir formation.This additional stress is called stress disturbance,the stress plus stress disturbance is called total stress.A lot of practices have shown that,stress disturbance has influence on the indirect effects of hydraulic fracturing,including the complex fracture network and long-term diversion mechanisms,which will at last influence the production of natural gas.Therefore,the control and adjustment of indirect effects is a key technology in assuring a high efficiency,long-term stability of natural gas production.However,to carry out a successful control,it is bound to establish a theoretical model of stress disturbance.In this paper,we are devoted to establish a theoretical model of stress disturbance in hydraulic fracturing,by combining the methods of analytical modeling,numeric simulation,and experiment test.We firstly study temporal variation of stress over a RVE,then study the full field distribution of stress disturbance by numeric simulation,and at last observe the stress disturbance in the samples in lab hydraulic fracturing test.The main conclusions are these:(1)The variation of stress disturbance on RVE is that,in the initial stage of hydraulic fracturing,stress disturbance increases in compression until attains a peak magnitude,then falls to a stable level with the cohesive breakdown continues.(2)The temporal variation of stress disturbance is determined by fracture propagation regimes,which is a basic physics produced by the coupling and matching between the technique parameters.(3)The numeric simulation reveals that the spatial distribution is an ellipse area around the main fracture conforming to the pore pressure distribution.The position at the fracture plane has the maximum magnitude,and along the path normal to the fracture plane,the magnitude of stress disturbance is decreased following a negative power law.(4)The hydraulic fracturing experiments show that,the stress disturbance around the wellbore is complex which may be affected by porosity and crack distribution over the samples,the stability of confining stress,fluid hold on time in the samples and size scale of samples.The completed tests shown that,brittle samples bring out multiple fractures which will induce stress interference,and further brings out complex stress disturbance.71 figures,13 tables,and 86 references.