Innovative Geomechanical Approach Lead to Successful Drilling of the First Highly Deviated Well at the Kruzenshternskoe Field
Authors: Zadvornov Dmitriy Alexeevich , Grachev Oleg Valeryevich , Maximov Danil Alexandrovich , Pekshev Dmitriy Vasilievich , Korelskiy Evgeny Pavlovich , Pavlov Valeriy Anatolievich 
Published: October 2016

Abstract
In this paper, we describe the use of an innovative approach in the preparation process of the input log data for predrill geomechanical modeling, as well as real-time wellbore stability model update during drilling. The paper presents the methodology and justification of the solutions found to restore the missing data in "slow" formations with low values of the speed of passage of acoustic waves at shallow depths for geomechanical modeling, detection and prevention of risks during well construction.
In the context of the "slow" formations at shallow depths (up to 1200-1400m TVDSS in the Yamal region), as well as logging tools restrictions, it is often impossible to detect shear acoustic waves, which, along with the compressional acoustic wave and other log data is also necessary for geomechanical modeling. Given these circumstances, and due to the inability of recording full-wave wireline acoustic logging conducting geomechanical modeling for the upper sections of the well is very difficult. Based on the analysis of acoustic logging data in the Yamal region, we have managed to build a regional dependence of compressional and shear acoustic waves and generate synthetic recovery of the shear wave velocities in the zones of missing data, which has been confirmed by the actual loging while drilling data.
The result of the discovered regional dependence of compressional and shear acoustic waves was the restoration of the missing portion of the upper interval logging that has allowed to carry out predrill geomechanical wellbore stability calculations in the absence of the necessary log data. Because of predrill geomechanical modeling during project preparation for the construction of the well it became possible to substantiate the need for adjustments in the project documentation regarding the use of project specific mud weights. According to this model, significant collapse of the borehole wall was possible in the case of expected design specific mud weights. Thus, the specific mud weight have been significantly adjusted for each section. The resulting dependence has also been used during the drilling process, in the cases when it was not possible to obtain correct shear wave velocity logging data due to external factors. These adjustments to the drilling program on the stage of well design, combined with the early identification and prevention of drilling risks based on constantly updated geomechanical model played a key role in the accident-free drilling of the first directional well with inclination angle of more than 70 degrees in the field.
The experience and achievements have also been used in a number of similar projects in the Yamal region, where it was possible to get a satisfactory convergence of the reconstructed and actual data, which enables the use of findings on the other projects of Yamal region.