Abstract
Wettability plays a significant role in the exploration and development of shale oil. The wettability affects the oil enrichment and restricts the selection of fracturing fluids. Shale is composed of complex minerals and organic matter. The pores composed of inorganic minerals have water wettability, while the pores composed of organic matter show the characteristics of oil wetting. The contact angle experiment and the spontaneous imbibition experiment are the most commonly used methods for characterizing wettability. The Qingshankou Formation in the Songliao Basin has thick source rocks, which is a favorable interval for shale oil exploration and development. Strengthening the wettability research in this area is of great significance for the exploration of shale oil. The wettability of different lithofacies shale in the northern Songliao Basin is seldom characterized, and there is a lack of comparative studies on contact angle and imbibition characteristics. In view of this situation, the shale of the Qingshankou Formation in the northern Songliao Basin has been classified. This article used the method of spontaneous imbibition combined with nuclear magnetic resonance to characterize the wettability of shale and analyze the influencing factors of the wettability of different shale lithofacies. Six samples with different lithological characteristics were used for this experiment. The study found that the imbibition results of samples with different lithofacies are different. The imbibition of sandy interlayer is less affected by the direction, while the imbibition of shale is more affected by the direction. The water imbibition volume of the sample is related to the content of clay minerals. The relationship of water imbibition volume in different lithofacies samples is as follows: low organic matter laminated siliceous shale > high organic matter massive clay shale > sandy interlayer > high organic matter laminated siliceous shale > high organic matter massive siliceous shale. Excessive content of clay minerals will cause shale to absorb water and expand and block pores, which is not conducive to further water imbibition by shale. The volume of oil imbibed is related to the organic carbon content. The relationship of oil imbibition volume in different lithofacies samples is as follows: high organic matter massive clay shale > high organic matter laminated siliceous shale > sandy interlayer > low organic matter laminated siliceous shale > high organic matter massive siliceous shale. The higher the total organic carbon content, the more developed the lipophilic pore network, and the more the volume of oil imbibed by the sample.
Highlights
Wettability describes the properties of the interface between different phases
The reflux efficiency of fracturing fluid in some shale oil reservoirs is too low, which dramatically increases the cost of shale oil development. erefore, the problem of shale fracturing fluid loss has attracted the attention of a large number of scholars [5,6,7,8,9,10]. e academic circles generally believe that wettability is the main factor affecting the water spontaneous imbibition of shale and the primary mechanism that causes excessive water imbibition of shale
Dehghanpour et al [37] studied the wettability of shale in Fort Simpson (FS), Muskwa (M), and Otter Park (OP) in Horn River Basin (HRB) and measured the contact angle of oil and water in the air on the shale surface, and a spontaneous imbibition experiment was carried out using intact shale samples
Summary
Wettability describes the properties of the interface between different phases. In reservoir engineering, wettability shows the tendency of reservoir rock surfaces to be preferentially wetted by a fluid phase [1, 2]. E wettability of shale determines the affinity of the surface for oil and water, which affects the ratio of free shale oil in the pores of organic matter and inorganic minerals. Dehghanpour et al [37] studied the wettability of shale in Fort Simpson (FS), Muskwa (M), and Otter Park (OP) in Horn River Basin (HRB) and measured the contact angle of oil and water in the air on the shale surface, and a spontaneous imbibition experiment was carried out using intact shale samples. Six samples with different lithological characteristics were used for this experiment. e experiment uses contact angle measurement, spontaneous imbibition combined with nuclear magnetic resonance method, to characterize the wettability of shale with different lithofacies characteristics and analyze the influencing factors of the wettability of different lithofacies shale
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