Permeability evolution study after breaking of friction reducer in near fracture matrix of tightgas reservoir

Hydraulic fracturing is generally required for tightgas formation with low matrix permeability to achieve economic production rate. Slickwater fracturing is one of most commonly used technology. Friction reducer is the primary component of this fluid. During fracturing, million gallons of friction reducer fluid are pumped downhole to initiate fractures, and lots of fluid would filtrate into formation matrix. Due to the small pore size of tightgas reservoir, breaking of the friction reducer fluid is required to minimize formation damage and improve the conductivity in fracture. However, this performance in tightgas is not clear. In this paper, tightsand samples were treated with a friction reducer and a breaker to simulate the filtration process during hydraulic fracturing. Three breaking scenarios were proposed and studied correspondingly. Over balance breaking resulted in higher permeability regain than balance and under balance breaking, which means less formation damage to the near fracture matrix. The short sample has a full recovery of permeability with over balance breaking and it is higher than that with balance and under balance breaking. With over balance breaking, 0.012 wt% breaker recovers 79.5% permeability, and the permeability regain increases with higher breaker concentration. The permeability regain of longer sample is improved, up to 116.3%. With under balance breaking, 0.1 vol% friction reducer shows 81.6% permeability regain. Lower concentration friction reducer achieves a higher permeability regain. The reasons can be attributed to pore blocking effect and wettability alteration introduced by the friction reducer and breaker. The emulsion particle size in the friction reducer solution is found to overlap with the pore size distribution of tightgas sandstone. Therefore, it was able to block the matrix pores in tightsand after treated with the friction reducer and breaker. The contact angle on sample surface was changed from 24.3° to 81.1° in average.