Wellbore stability analysis based on a new true-triaxial failure criterion i Abstract A main aspect of wellbore stability analysis is the selection of an appropriate rock failure criterion. The most commonly used criterion for brittle failure of rocks is the Mohr-Coulomb criterion. This criterion involves only the maximum and minimum principal stresses, σ 1 and σ 3 , and therefore assumes that ...

Pore gas has a significant influence on rock strength. This study performed triaxial compression tests of gas-infiltrated sandy shale samples to investigate the strength characteristics under gas pressures of 0 and 2 MPa. The effective stress coefficient was evaluated while considering the gas and solid coupling effect, and was found to decrease with increasing confining pressure. The calculate...

wellbore instability is a quite common event during drilling, and causes many problems such as stuck pipe and lost circulation. it is primarily due to the inadequate understanding of the rock properties, pore pressure, and earth stress environment prior to well construction. this study aims to use the existing relevant logs, drilling, and other data from offset wells to construct a precise mech...

A new failure criterion was presented to predict the ultimate strength of shale under the triaxial and polyaxial state of stress. A database containing 93 datasets was obtained from the results of the uniaxial, triaxial, polyaxial compressive tests, an indirect tensile test was collected from reliable references, and this test was carried out on the shale samples taken from the southwestern oil...

Wellbore instability is a quite common event during drilling, and causes many problems such as stuck pipe and lost circulation. It is primarily due to the inadequate understanding of the rock properties, pore pressure, and earth stress environment prior to well construction. This study aims to use the existing relevant logs, drilling, and other data from offset wells to construct a precise mech...

Strength of rocks in the confined tension region, where minimum principal stress is tensile, has only infrequently been measured and not well understood. Quasi-static Brazilian tests under a range confining stresses (2.76 to 27.58 MPa) used determine strength sandstone region. The test results indicate that region was strong function intermediate stress: increasing significantly increased sands...

Abstract Wellbore instability problems cause nonproductive time, especially during drilling operations in the shale formations. These include stuck pipe, caving, lost circulation, and tight hole, requiring more time to treat therefore additional costs. The extensive hole collapse problem is considered one of main challenges experienced when Zubair formation. In turn, it caused by increasing wel...

The failure of rocks subjected to a general state of stress (σ1 ≥ σ2 ≥ σ3) has been studied since the pioneering true triaxial experiments conducted by Mogi [1]. In true triaxial tests, cuboidal specimens are subjected to fixed, and typically unequal, σ3 and σ2, while σ1 is increased until failure occurs (expressed by σ1 at failure, or σ1,peak). For each constant σ3, σ2 is varied from test to t...

Abstract Borehole breakout initiation, progression, and stabilization are modeled using a semi-analytical method based on Melentiev’s graphical conformal mapping procedure, Kolosov–Muskhelishvili complex stress potentials. The only input data required the elastic moduli of rock, Coulomb strength parameters (cohesion angle internal friction), far-field stresses. stresses around borehole wall com...