Research on Mechanism and Main Controlling Factors of Nano Surfactant Imbibition Oil Displacement in Tight Reservoir
Authors: Zhang L. , Xu H. , Wang J. , Jiang H. 
Published: September 2023

ABSTRACT
Nano-surfactant is affected by multiple factors. Therefore, it is necessary to study the influence of different factors on the spontaneous imbibition displacement efficiency of nano-surfactant and determine the main control factors affecting the imbibition displacement efficiency. The interaction mechanism between nano-displacement agent and tight oil reservoirs is revealed, and a systematic evaluation method for the interaction mechanism between nano-displacement agent and tight oil reservoirs is established in this paper. The mechanism and main control factors of nano-surfactant imbibition oil displacement in tight oil reservoirs were tested and analyzed, too. The research shows that (1) The nano-particle size structure of nanoemulsion helps to reduce the adsorption of surfactant in the formation. (2) Nanoemulsion will not block the formation and can enter the deep part of tight reservoir. (3) The interfacial tension of nanoemulsion can reduce the seepage resistance on the one hand, and provide power for imbibition replacement on the other hand. (4) The wettability reversal function can convert oil-wet rock into water-wet rock and promote imbibition. (5) Under the same conditions, temperature has great influence on the effect of imbibition. The research results provide strong theoretical and technical support for the further efficient development of tight reservoirs.

INTRODUCTION
With the development of science and technology and economy, people ‘s demand for oil and gas resources is increasing. Conventional oil and gas resources can no longer meet the current energy supply and demand. After decades of development, the resource exploitation technology of tight oil and gas resources has become increasingly mature, and tight oil and gas resources have occupied an increasingly important position in the exploration and development of global oil and gas resources (Khlaifat, 2011). Tight oil refers to the oil accumulation that occurs in the source rock in the form of adsorption or free state, or in the reservoir rocks such as tight sandstone and tight carbonate rock adjacent to the source rock, without large-scale long-distance migration (Zhou, 2020,2021; Li, 2015; Jia, 2012). Due to the existence of a large number of micro-nano pores in the tight reservoir, the pore structure of the tight reservoir is extremely complex, and the fluid flow inside the reservoir is difficult. However, the existence of micro-nano pores also increases the capillary force in tight reservoirs and enhances the driving force of imbibition (Li, 2015; Jia et al., 2012; Xie, 2013; Liang, 2020; Liang et al., 2018; Penny et al., 2012; Erfani Gahrooei et al., 2017; Liu et al., 2021; Wang and Yang, 2021; Yu and Su, 2015). Because most of the tight oil reservoirs are soaked in crude oil for a long time, the surface of the reservoir is wetted by oil phase, and the capillary force is imbibition resistance. By adding nano-surfactant to the injected water or fracturing fluid, the oil-wetted reservoir is modified to water-wetted, which can achieve the purpose of promoting imbibition and energy-increasing replacement. It is also the main measure to improve the imbibition capacity of foreign fluids in tight reservoirs.