The Imbibition Mechanism and the Calculation Method of Maximum Imbibition Length during the Hydraulic Fracturing

It has been recognized that fluid imbibes into the matrix and floods the oil during hydraulic fracturing; however, the mechanism of fluid imbibing into the matrix and flooding the oil remains unclear. Additionally, there is a scarcity of methods for calculating the maximum imbibition length. In this paper, we first analyzed the imbibition mechanism during hydraulic fracturing and then developed a method for calculating the imbibition length using mercury intrusion experiments, seepage theory, and numerical calculations. By comparing the proposed method calculations with experimental results and published model calculations, we verified our proposed method. Finally, we presented the influences of the maximum imbibition length. From the work, we can know that imbibition during hydraulic fracturing involves counter-current imbibition under surrounding pressure. The influence of permeability on threshold pressure gradients was found to be greater than that on capillary pressure, resulting in an increase in the maximum imbibition length with increased permeability (ranging from 0.01 to 0.2 × 10⁻³ μm²), while the time taken to achieve the maximum imbibition length decreased exponentially. When the reservoir permeability was 0.1 × 10⁻³ μm², the contact angle was 60°, and the interface tension was 50 mN/m, the maximum imbibition length was 1.8 m, and the time of achieving maximum imbibition length was 70 days. This study provided a method for evaluating the extent of imbibition.