Flowback laws and control parameter optimization of shale gas wells

Postfrac flowback plays a key role in connecting the fracturing and the later production. At present, the selection of postfrac flowback control parameters of shale gas wells and the formulation of flowback mechanism are still in the exploratory stage, the effects of flowback control parameters on the flowback ratio and production rate of shale gas wells are not defined clearly, the shut in time of flowback and the utilization and replacement of flowback choke are basically based on experience and fixed models. Abundant flowback data of shale gas wells in one block were analyzed and the effects of flowback speed and action between fracturing fluid and shale during fracturing + shut in on flowback ratio and production rate were studied. And accordingly, the flowback method after the killing of shale gas well was confirmed and the following conclusions were reached. First, the increase of flowback ratio makes contribution to the increase of shale gas well productivity, but flowback ratio is not the key factor controlling the numerical value of gas well productivity. Second, the shut in of shale gas well after the fracturing is favorable for the continuous propagation of hydraulic fractures and the increase of single well production, but if the shut in period is too long, a large amount of fracturing fluid will be detained in the reservoir, and consequently the reservoir is damaged and the productivity of gas well is decreased. It is pointed out that low speed flowback in the early stage of well startup is more favorable for the increase of flowback ratio and single well productivity. And it is recommended to adopt the flowback mechanism of "choke based control, gradual enlargement, continuity and smooth". The flowback laws and control parameter optimization results of shale gas wells provide the basis for the optimization of flowback control parameters after the fracturing of shale gas wells in this block.