The Effect Of Fracture Network Structure Of Shale Gas Reservoir On Frac-water Flow-back

Hydraulic fracturing technology plays a key role in achieving industrially development of shale gas.Field practice demonstrates shale gas reservoir post-frac flow-back rate is unexpected low,and there is no law found between flow-back rate and well performance,beyond the conventional explanation in which high flow-back rate always means good well performance.There is still no a complete solution to the problem.Fracture network structure maybe the key in giving insights into the problem.From the perspective of fracture network structure,on the basis of mass conservation principle and energy conservation principle,experiment and model research has been done to give insights into the mechanisms of frac-water loss and flow-back.The results demonstrate that matrix imbibition and hydraulic energy dissipation are the main fluid-loss mechanisms.The release of residual hydraulic energy,which saved in the way of elastic energy,and reservoir gas dilatation energy are responsible for frac-water flowback.The effect of fracture network structure on gas-drive flowback rate depends on matrix imbibition and flowback energy.The effects of fracture network structure on flowback characteristics include imbibition area,ability to save hydraulic energy,exposed area to release shale gas,conductivity.A complex fracture network always means a low early elastic flowback rate for a limited storage of hydraulic energy.The effects of fracture network structure on gas-drive flowback rate depend on the quantity of matrix imbibition and flowback energy.The results of this study have been proved reliable by hydraulically fractured shale gas well flowback data.Fracture network structure is also closely related to well performance,therefore,this study in which the effects of fracture network structure on flowback rate has been investigated,may help productivity evaluation,matrix imbibition estimation and flowback strategy formulation.