Tezislər / Theses

Figure 3.
Third stage–shale conditions 
after caving 

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THE 3
rd
 INTERNATIONAL SCIENTIFIC CONFERENCES OF STUDENTS AND YOUNG RESEARCHERS 
dedicated to the 99
th
anniversary of the National Leader of Azerbaijan Heydar Aliyev
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coupling model, in which the chemical potential is the linear graph of solute 
mass proportion. After, the linear chemistry-pore-thermoelasticity coupling 
model is created by Ghassemi, et al., which assumes the effect of chemical 
potential and temperature, but does not assume the influence of diffusion 
potential of drilling mud on hydration osmosis. According to the pore elasticity 
theory, a nonlinear fluid-solid-chemical coupling model was established, In 
this model, three aspects were improved from the previous models. The first 
aspect is the reaction of expansible shale, which is full of saturated fluid, is 
altered by hydration osmosis. The model presumes the influx of fluid flow and 
ion diffusion on solid deformation. Second, the model considers the influence 
of diffusion potential on hydration osmosis. Negative charges on clay 
surfaces can suspend negative ions to diffuse through the medium in most 
shales. But the positive ions would be attracted by the negative charge wall, 
which makes the shale have the ion-selective membrane ability. Thus, the 
formed diffusion potential becomes one of the driving forces of hydration 
osmosis. The third model assumes the nonlinearity of ion diffusion. Because 
the chemical potential is not a linear function of the mass fraction of solute, 
the linear model of ion diffusion alleviates the hydration osmosis process. A 
new nonlinear fluid-solid-chemical coupling model was applied in 
determining the borehole instability problems of special wells to discover and 
compare the validity of the new model.
Yew and Lew (1992) proposed a theory of pore elasticity in the wellbore 
instability model to study the effects of porous fluid influx on wellbore stability. 
The influx of pore fluid causes additional normal stresses, which in some 
cases disrupt the stability of the wellbore. 
After studying the local stresses and rock strength, the stability of the 
wellbore is estimated according to the selected deformation criteria. Tension 
and strength change when clay gets in contact with a fluid. Therefore, 
chemical effects must be added to the mechanical effects. 
Chenevert (1970) found that reactive clays tend to adsorb water from 
the drilling mud, and if their chemical potential (water activity) is less than the 
drilling mud, then the clay will swell [3]. With this concept, Chenevert 
developed the theory of "balance of activity" in 1970. According to this theory, 
drilling with oil-based drilling mud is more efficient [4]. Due to the water 
activity of clays drilled with oil-based drilling mud is the same or slightly lower 
than the solution, the wellbore is stable. However, this theory does not show 
the effectiveness of WBM. The reason for this is the process of ion flow in 
and out of the clay due to the difference in concentration. Bord (1984) studied 
that the adsorption of water on reactive clays such as smectite causes a 
reversible increase in the volume of the mineralogical structure. In this case, 
a gap of 10-18 *10
-10
m is formed between adjacent clay particles.

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