The Spontaneous Imbibition of Micro/Nano Structures in Tight Matrix and the Influence on Imbibition Potential

Abstract

Tight matrix has relatively low permeability and porosity, with abundant micro/nano pores. The capillary force in these pores are relatively strong, making the wetting liquid easier to be imbibed in the matrix. This process is called spontaneous imbibition. The complexity of pore structure is identified as one of the key factors influencing the imbibition process, but the detailed mechanism is not clear. Thus, in this work, a method is proposed to evaluate the influence of pore structure on imbibition process. Pore structure has fractal properties in a specific scale. By using the fractal theory, an imbibition model is provided to analyze the influence of microscopic structures on spontaneous imbibition, considering the pore size distribution and pore connectivity. Also, based on this model, the influencing factors on dimensionless imbibition and diffusion rate are discussed. Results show that the pore structure has more branches, larger and shorter sub-throats has higher chance to gain a high imbibition rate. Finally, a 3D imbibition parameter cube is constructed to determine the parameter combinations in favor of strong water diffusion potential. By utilizing the analysis method based on the fractal theory, we can effectively evaluate the imbibition potential. It is helpful to provide a guidance to evaluate the water imbibition to gas production.

NMR Investigation of Brine Imbibition Dynamics in Pores of Tight Sandstones under Different Boundary Conditions

“…The result implies that the sample with the TEO boundary condition had the largest diffusion ability, while TEC had the lowest diffusion ability. This nature of the curve was obtained by Li et al, where the diffusion ability was compared for different core samples. Higher diffusion ability depicts a greater gas displacement effect and improves production of gas.…”

“…Similar zones have also been observed elsewhere. , However, some variations in the imbibition profiles were observed because of the different boundary conditions. It is noteworthy that the direction of the core sample does not have any influence on the imbibition profile because the sample is fully immersed in water …”

“…Imbibition capacity ( V c ), which is the ratio of the maximum imbibed volume ( V imb,sat ) to the pore volume ( V p ), is obtained for each boundary condition as The diffusion ability was calculated as the ratio of the cumulative fluid imbibed (normalized by the pore volume) within the diffusion region to the total (maximum) fluid imbibed. This parameter represents the contribution of diffusion during imbibition under each boundary condition The imbibition rate across the entire sample is the average volume flow rate ( ), which is given in terms of the water content by eq …”

“…This parameter represents the contribution of diffusion during imbibition under each boundary condition The imbibition rate across the entire sample is the average volume flow rate ( ), which is given in terms of the water content by eq Finally, the imbibition potential ( P imb ) for each boundary condition is evaluated as the ratio of the volumetric imbibition rate in the diffusion part to the volumetric rate in the capillary dominated part ( R D / R PC ), as explored by Dehghanpour et al This dimensionless parameter is calculated using eq as …”

Effects of Microscopic Pore Structures on the Spontaneous Imbibition of Longmaxi Shale

“…A soaking process, referring to an extended shut-in period, is commonly reported in shale gas wells after fracturing treatment. Theoretical and experimental studies have demonstrated that spontaneous imbibition (SI) plays an important role in the distribution of fracturing fluids during the soaking process (e.g., refs − . Additionally, studies have demonstrated that imbibition during the soaking process can improve the production performance of shale gas wells. − Consequently, studying the SI behaviors is of great significance to improve the understanding of gas recovery from shale reservoirs.…”