Flowback cleanup mechanisms of post-hydraulic fracturing in unconventional natural gas reservoirs

Abstract

This work investigates the fracturing fluid cleanup mechanisms of post-hydraulic fracturing in unconventional gas formations by studying a large number of wide-ranging parameters simultaneously.
In this work, different scenarios of the cleanup operation of the hydraulic fracturing process are considered. This study consists of investigating the post-fracturing cleanup operation of hydraulically fractured vertical wells (VW) and multiple fractured horizontal wells (MFHWs). Additionally, the impact of soaking time, the range of the matrix permeability, applied drawdown pressure, injected fracturing fluid (FF) volume, fracture spacing and horizontal well length has been investigated by running different sets.
Results show that that the trend of the impact of relevant parameters for VWs and MFHWs are analogous excepting the matrix permeability, km. That is, in the MFHW base reference set, the effect of matrix permeability on capillary pressure is more significant than that on fluid flow while the reverse is observed for VW. The difference in the impact of km in VWs and MFHWs is attributed to the geometry of the fluid flow towards the production well and different well completion scheme.
It is also concluded that the impact of parameters affecting the capillary pressure in the matrix is more significant for MFHWs whereas matrix and fracture mobility pertinent parameters are more important for VWs than MFHWs. As a result, larger matrix capillary pressure values are more vital in the cleanup of MFHWs because of more imbibition of FF into the matrix and subsequently lower conflict between the flow of gas and FF in the fracture.
The other part of this research concentrates on the impact of IFT reducing agents on the post-fracturing production in different formations. In hydraulic fracturing operations, these agents are commonly used as an additive in fracturing fluid to facilitate its backflow by reducing Pc and subsequently enhancing gas production. The results of this work recommend that using such agents enhances the gas production rate for ultratight formations but not for tight formations (it reduces the gas production rate). Therefore it is not suggested to use such agents in tight formations.
The findings of this work improve the understanding of fracture cleanup leading to better design of hydraulic fracturing operations in unconventional formations.