No abstract

SUMMARY Researchers base their analysis on basic drilling parameters obtained during mud logging and demonstrate impressive results. However, due to limitations imposed by data quality often present during drilling, those solutions often tend to lose their stability and high levels of predictivity. In this work, the concept of hybrid modeling was introduced which allows to integrate the analytical correlations with algorithms of machine learning for obtaining stable solutions consistent from one data set to another.

The traditional considerations and guidelines regarding well planning were not applicable to the challenges that extended reach well #101 of the Uzen field have presented. On the one hand, the reservoir itself was shallow, highly heterogeneous and structurally complex. On the other hand, the well trajectory involved the long interval placed nearly parallel to the bedding of catastrophically unstable shales. The importance of geomechanical study and mud weight optimization have become very clear after reaching TD of 295.3mm section. There were no signs of instability while drilling, however the pulling out of hole was impossible without rotation, the overpulls, torque and pressure spikes resulted in fracturing the well and circulation loss, the well conditions imposed the high risk of BHA LIH. The mud was gradually weighted up from 1.15 sg to 1.40 sg according to geomechanical calculations performed in a short time. After having conditioned the mud and performed several circulation cycles the drilling string was safely extracted out of hole. Due to the highly unstable hole conditions, the decision was to sidetrack the new borehole. The main adjustment of the new trajectory of well #101 was dropping as much as possible the inclination angle when drilling through shales, at the same time allowing the maximum distance to water-oil contact. The PDM was planned to be used in the interval with high dogleg while where extended intervals of well trajectory went subparallel to bedding, the RSS was preferred, as there was a high need for lower vibrations and better cleaning quality. The morning meetings included the reports and discussion of all the involved parties: Volga Gas management, mud and drilling engineers, geomechanicists, mud loggers and geologists. The thorough inter-disciplinary analysis was performed before making any decision: routine (time and number of reaming after drilling the stand, tripping speeds, circulation timing and duration) and strategic (trajectory change, geostopping, place to perform sidetrack, completion optimization, etc) too. The holistic approach of risks’ assessment and the proactive management resulted in drilling success of the first horizontal well in the field (2480m MD, 717m TVDSS). It was drilled safely and efficiently, allowing to access the reserves, delay the onset of water production, accelerate time to reach planned production level, and increase cumulative production of oil. The success of the drilling performance was publicly acknowledged by Volga Gas.

This article is continuation of geomechanical estimations for wellbore stability and horizontal wells drilling optimization to M formation of the Boca de Jaruco oilfield, Republic of Cuba. Following the completion of the first part of the work presented in the article SPE-196897-RU, the first horizontal wells were successfully drilled. In the first part of the work, the stress-state analysis and horizontal in-situ stresses directions were analyzed using pressure behavior during steam injections, cross-dipole acoustics, as well as data from oriented caliper from vertical wells. As a result, according to the recommendations, an additional study in the deviated sections of the wells, including core sampling and micro-imager logging were conducted. Presence of wellbore failures at the inclined sections allowed to use the method of inverse in-situ stress modeling based on image logs interpretation. The main result of the work were the determination of the stress state and horizontal stresses direction, as well as classification of the failures detected using the image log into groups. Moreover, the genesis of breakouts which had deviation from each other different that 180° were evaluated.

In this paper, some features of conducting experiments on core samples to determine mechanical properties were established. Detailed description for such type of testing is poorly described in regulatory documents (Russian State Standard, ASTM). Problem of specific test methods selection in accordance to task before the geomechanical modeling is considered. For the most issues, a series of experiments to build a failure envelope is required. Details of sample preparation for compression tests are regarded. In particular, the advantages and disadvantages of different methods for preserving in-situ core saturations are discussed: the collection of an isolated core with subsequent conservation or the preparatory work with the extraction, drying and saturation of samples. While conducting multi-stage compression tests for building Mohr circles, chose of the right moment to stop the loading stage has a significant effect to prevent destruction of the sample in the early stages. This paper demonstrated that for specimens characterized by a shear failure type, it is recommended to focus on the plot "axial stress - volumetric strain". In particular, the inflection point of the curve, that is the moment of reaching the maximum value of volumetric deformation could be selected as a criterion for the loading stage termination. For samples with high porosity, a complete testing cycle to build the Mohr circles and the entire failure curve is given.