Evaluation of the Pore Structure Variation During Hydraulic Fracturing in Marine Shale Reservoirs

Hydraulic fracturing becomes a necessary method to exploit shale gas, and the imbibition behavior of fracturing fluid can cause the pore structure variation. At present, the evaluation of this variation has less been investigated, and repeated imbibition was conducted to research the variation of pore structure. First imbibition was conducted as simulating the pore structure variation during hydraulic fracturing, and repeated imbibition was carried out to appraise this kind of variation. Two significant parameters were proposed to estimate the pore structure variation, which are the differential value of initial imbibition rate and the utmost differential value of normalized imbibed volume. Initial imbibition rate is closely related to pore connectivity, and normalized imbibed volume reflects the pore volume. Reservoirs with a higher value of these two parameters have advantage for developing its resources. Sichuan Longmaxi formation has the highest value in both parameters among all formations, which showed that Sichuan Longmaxi formation has advantage for exploiting its resources by hydraulic fracturing. Baojing Longmaxi formation, Sichuan Niutitang formation, and Cengong Niutitang formation have a lower value in both two parameters which indicated that these formations have less potential to develop its resources by hydraulic fracturing. These two parameters are mainly influenced by wettability and initial permeability, and have no obvious relationship with clay content. Overall, our research is conducive to screening the ideal formation for exploiting shale gas by hydraulic fracturing.