Analysis of Dynamic Imbibition Effect of Surfactant in Microcracks of Reservoir at High Temperature and Low Permeability

Abstract

Summary The objective of this work was to explore the dynamic imbibition effect of a surfactant solution in the microcracks of a reservoir at high temperature (83.3°C) and low permeability (2 × 10−3 µm2), as well as the relative influencing factors. This study considered Fuyu Reservoir of the Toutai Oil Field in Daqing, China, which has high-temperature and low-permeability characteristics, as a research platform. First, the optimal surfactant type and concentration were selected by evaluating the imbibition recovery through a study of the adhesion-work-reduction factor and the ratio of the capillary force and gravity (NB−1), under the conditions of a spontaneous-imbibition experiment. Then, through a dynamic imbibition experiment, this study investigated the effects of the injection velocity, wettability, and saturation of the matrix on the dynamic imbibition recovery. Both the experimental results and practical application showed that the surfactant could effectively improve the imbibition recovery. However, in the process of choosing a surfactant, one must consider the influence of interfacial tension (IFT) on the capillary force when reducing the adhesion work to improve the displacement efficiency. A suitable injection velocity should be chosen to take full advantage of the ability of the capillary force to “absorb water and discharge oil,” as well as the “displacement function” of the viscous force and “improved wettability” provided by the surfactant, to obtain a higher imbibition recovery. Enhancing the water-wet state of matrix blocks can help to improve the seepage flow between the matrix and microcracks, which assists in increasing the imbibition recovery. Thus, a surfactant with an appropriate concentration or other chemical agents can be selected to enhance the water-wet state of matrix blocks. When a surfactant solution is used to develop a similar reservoir, earlier imbibition construction assists the capillary force to provide the function of “absorbing water and discharging oil,” which is helpful to enhance the imbibition recovery. The practical application of a surfactant solution in Well M38-S64 in the Mao 8 area showed that adding a surfactant to a water solution assists in improving the imbibition recovery.