Tezislər / Theses

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
78
Second (mechanical) approach. This approach is concerned with the 
mechanics of shale behavior once it is drilled. Bradley proposed a classical 
theoretical mechanical model based on the work by Fairhurst to predict 
wellbore stability by the selection of the proper drilling fluid density to stabilize 
the wellbore [1,2]. 
The quality of the mechanical stability model predictions is a function of 
the quality and quantity of the input data [6]. Most of the models did not 
consider the effect of temperature, shale hydration, and they assumed linear 
elasticity. 
Few researchers in the design of their experimental work tried to 
understand the behavior of shales mechanical effects and under the 
influence of the drilling fluids. Darley used reconstituted shale samples (from 
drilled cuttings) compacted at 8400 psi for 16 hours to study the three modes 
of wellbore failure by determining stresses developed when shale adsorbs 
water [5]. 
Third approach. Capillary suction time test (CST) was developed by 
Wilcox and Fisk to characterize shales and to study shale dispersion and 
filtration properties at the rig site [8]. One disadvantage of this test was that 
it essentially measures the ability of the powdered shale to control filtration, 
a test not directly related to shale inhibition.
In 1987, Chenevert and Osisanya developed some quick and easy-to-
run tests for use at the rig site for the evaluation of shale-drilling fluid inhibition 
[9]. In this regard, the swelling, dispersion (hot-rolling), and cation exchange 
capacity tests were found to be the most useful.

Wellbore instability results from chemically reactive shales (drilling fluid 

effects) or from unfavorable earth stresses (rock mechanics effects), or a 
combination of these two effects. The most common and probably the more 
severe and expensive wellbore instability is caused by reactive shale 
formations. 
The three stages of wellbore instability due to shale-drilling fluid interaction 
were documented recently by Chenevert and Osisanya [8]. In the first stage, 
the shale is compacted due