Evaluation of fracturing fluid imbibition and water blocking behavior in unconventional reservoir

Imbibition is believed to be beneficial to the production. However, the load recovery is low, and water blocking can have a marked impact on the production This study aims to evaluate imbibition and water blocking behavior in tight reservoir, and reveal the impact of micro pore structure on imbibition and water blocking. Low-pressure nitrogen gas adsorption (LP-N2GA), high-pressure mercury injection (HPMI), rate-controlled mercury injection, nuclear magnetic resonance (NMR), imbibition experiments and centrifugal experiments were comprehensive used. Micro pore structural characteristics and the distribution of fracturing fluid in pores were examined. The fluid can enter the small mesopores first or the mesopores first. Imbibition recovery (IR) range is 35.82% to 94.17%, and average is 63.63%. After centrifugation, irreducible water saturation (Swir) range is 3.43% to 57.84%, with an average of 17.28%. Permeability damage rate range is 15.19% to 97.86%, with an average rate of 51.88%. Factors that affecting IR include average pore throat ratio (APTR), specific surface area (SSA), permeability, porosity, pore volume (PV), average throat radius (ATR) and average pore radius (APR). Factors affecting water blocking include permeability, APR, ATR, porosity, PV, APTR and SSA. Permeability has the maximum impact on fluid distribution and flow, followed by APTR, porosity, and APR.