Tezislər / Theses

 
to the Overburden stress and is only partially
 
hydrated (Figure 1). This relatively dehydrated shale condition provides a low 
aqueous chemical activity within the shale, which when exposed to a higher 
aqueous chemical activity wellbore fluid, creates a swelling process and 
resulting rock stresses. Such aqueous chemical activity imbalances are 
estimated to produce swelling pressures as high as 10000 psi. 
The second stage is when the shale has just been penetrated and the 
drilling fluid and ions are free to move into and out of the shale (Figure 2). 
The water and the ions are attracted to the clays in the shale as a result of 
the imbalance in the aqueous chemical drilling activities of the various 
elements. 

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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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Figure 1. 
First stage-shale conditions
Figure 2. 
Second stage-shale conditions
before drilling after drilling
The third stage occurs when 
additional water moves into the clays in 
the shale. Swelling stresses are 
developed until failure occurs and shale 
cavings are produced, resulting in 
wellbore
 
enlargement (Figure 3).
Based on thermoelasticity theory, a 
quantification model of hydration effect 
was created by H. Rongzun, et al., and 
Yew, et al. which ascribes hydration 
alterations to total water volume. In this 
method, rock expansion strain is defined 
only by water volume. It is not about the 
significance of chemical interaction 
between drilling mud and shale. Hale et 
al. used semi-permeable membrane 
equivalent pore pressure theory on the 
interaction between WBM and shale.
The effect of water influx due to pressure differences in the shale was 
disclaimed. Also, the effects of ion diffusion and exchange on shale hydration 
were refused. According to the thermodynamic law and Gibbs-Duhem 
equation, the coupling model of suction expansion is created by Heidug et 
al. In this model, the osmosis, expansion, and solute penetration between 
water phase in the drilling mud and pore water in shale is supposed. This 
method does not assume the joint effect of pore pressure of fluid and rock 
deformation. Ghassemi, et al. created a linear chemistry-pore elasticity