Novel Analytical Model of Shale Spontaneous Imbibition Considering the Hydration Effect

Abstract

Shale gas has enormous potential and has become a hotspot in recent decades. To exploit shale gas, a variety of working fluids (drilling fluid, fracturing fluid, etc.) have to be applied in drilling and well-completion engineering. When fluid contacts with shale, spontaneous imbibition occurs, affecting wellbore stability, fracturing fluid loss, and shale gas production. In the past few years, numerous researchers conducted studies on shale spontaneous imbibition, yet the vast majority of their works are derived from conventional method based on sandstone and carbonate. One of the characteristics of shale is strong hydration, which has been widely reported. During the interaction between liquid and shale, spontaneous imbibition is accompanied by hydration. Shale hydration mainly involves two aspects, i.e., osmotic pressure and hydration structural damage. Now there is still no research on studying the hydration effect during spontaneous imbibition, and how hydration affects spontaneous imbibition is still not fully understood. Therefore, in this paper, considering osmotic pressure and hydration structural damage, spontaneous imbibition in shale formation has been investigated. Besides, according to the Hagen−Poiseuille law, a novel analytical model has been established by coupling imbibition and hydration. In comparison to experimental data of spontaneous imbibition, practicability of this spontaneous imbibition model has been verified. On the basis of this new model and spontaneous imbibition test, influences of salinity and hydration on shale spontaneous imbibition have been systematically discussed. Results indicate that salinity reduces spontaneous imbibition by lowering the driving force of imbibition and restricting hydration damage. Hydration structural damage is its major influencing mechanism for shale spontaneous imbibition. In the shale exploitation, this model can offer guidance for evaluating fracturing fluid loss and hydration damage, which are practical for drilling and hydraulic fracturing design. Besides, the outcome of this paper is beneficial for improving our understanding on spontaneous imbibition in shale formation.

Imbibition Mechanisms of Fracturing Fluid in Shale Oil Formation: A Review from the Multiscale Perspective

“…Accounting for the influences of the forced pressure and the viscous pressure loss, Zhong et al proposed an analytical model for the forced imbibition of fracturing fluid into a shale matrix. Ding et al take into account the hydration effect during spontaneous imbibition because new cracks develop through hydration structural damage, which changes the shale structure and provides a new pathway for imbibition (Figure (I)). The hydration coefficients of the average pore diameter and porosity are used to characterize the pore structure variations at any time.…”

“…Various capillary bundle models for the imbibition characterization: (I) curved capillary; (II) capillary bundle model including the organic and inorganic matter; and (III) spontaneous imbibition and forced imbibition in (a) clay and (b) brittle minerals . Panel (I) has been reproduced with permission from ref . Copyright 2021, American Chemical Society.…”

“…matrix. Ding et al113 take into account the hydration effect during spontaneous imbibition because new cracks develop through hydration structural damage, which changes the shale structure and provides a new pathway for imbibition (Figure9(I)). The hydration coefficients of the average pore diameter and porosity are used to characterize the pore structure variations at any time.…”

Correlation between Natural Seepage and Ionic Diffusion in Shales

“…It was verified by spontaneous seepage and absorption experiments. 10 Another aspect is to complement the results of the research core experiments through modeling. 11 As well as carrying out explorations of the combined nature of experiments and mathematical models.…”

Experimental investigation of nanofluid enhanced oil recovery by spontaneous imbibition

“…The spontaneous imbibition experiments were conducted using water or surfactant solutions. [15][16][17][18][19][20] Standnes et al 21 conducted spontaneous imbibition experiments using aqueous solutions of ethoxylated alcohol (EA) and a cationic surfactant (C12TAB). For the short core experiments, about 40-45% of the original oil in place (OOIP) was recovered using C12TAB, while only 10% was the average recovery using EA.…”