The task of choosing the sidetrack trajectory for drilling is one of the most common among specialists while workovers planning in oil and especially in gas fields. This task is solved by reservoir engineers, geologists and drilling engineers, both in a team and separately. Despite the widespread use of software for processing and analyzing the data and high automation of most routine tasks, many oil and gas companies lack a unified methodology for choosing sidetrack trajectory. Each oil and gas company has its own approach to this task. Usually, the process of analyzing candidates is based on the expert opinion of the well design engineer and has several limitations, such as:

  • Short deadlines - on average, it takes from two to three weeks to select the sidetrack drilling trajectory.

  • Low automation of the process of creating and analyzing the trajectory - the trajectory is created by a specialist manually, this process takes, considering the time for analysis, from two to four days for one trajectory. As a result, about five candidates are considered for the allotted time.

  • Analysis of a small number of influencing factors — two-dimensional maps of averaged permeability, residual reserves maps, a seismic map of average amplitudes, as well as the proximity of the candidate to the existing well stock are mainly considered during analysis of the trajectory.

  • Prediction of the flow rates is not always based on the hydrodynamic model - when calculating the candidate's starting flow rate due to tight deadlines, not all trajectories are analyzed using the hydrodynamic model, for part of the trajectories flow rates are calculated only using analytical techniques, such as the Joshi equation (Joshi, 2018).

  • The risk of human factor.

Sidetrack drilling, like other workovers, is aimed at increasing the flow rate of the well and the cumulative production of the entire field. In gas fields with falling production and high drilling density, sidetrack drilling can help significantly extend production time with the same level or increase production. Drilling a sidetrack, rather than a new well, can significantly reduce drilling costs, since the main well has already been drilled. Potentially, almost any well, especially with falling production rate or high water cut, can be a candidate for sidetrack drilling. According to the data from the Federal Supervision of Natural Resources in 2017, almost a quarter of all wells in Russia are inactive or shut, which is almost 60,000 wells.

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