Case studies and operation features of transient multiphase flow in low-flow wells with multistage fracturing and extended horizontal wellbore operated with ESP in PSA mode

Background. For industrial oil production from shale oil formations, it is necessary to drill wells with an extended horizontal wellbore (HW) and multi-stage hydraulic fracturing (MHF). During the entire life of the well, the rate of decline in production rates is well described by Arps curves. During the first year of operation, the rate of decline in production varies from 60 to 80%, wells become low-flow and to effectively extract oil from them it is necessary to use artificial extraction methods. The most popular and effective method today is an electric centrifugal pump (ESP), which is used both when operating in continuous mode and when operating in periodic short-term activation mode (PSA), which allows oil to be extracted from wells at flow rates not exceeding several tons per hour. When the ESP operates in the PCA mode, the flow in the well is unsteady, and to optimize operating modes it is necessary to use specialized simulators for modeling multiphase unsteady flow.

Aim. This work is devoted to the analysis and modeling of operating modes of low-flow wells with an extended HW and MHF during artificial lift with an electric submersible pump (ESP). The article provides a comprehensive analysis of the operating modes of wells in the Bazhenov formation with HW and MHF, operating with an ESP. Complications during the operation of ESPs in such wells are shown, associated both with the removal of proppant and with a constant decrease in productivity and an increase in the gas factor, and data on the operation of various types of ESPs in wells of complex design are provided.

Materials and methods. One of the main achievements of the work is the methodology for creating a model of multiphase unsteady flow in a well with an ESP operating in the PSA mode using specialized so` ware. To accurately describe the physical processes, various approaches were used to numerically simulate unsteady multiphase flows in a well with an ESP with a downhole separator. Difficulties that may arise during well operation were considered through the analysis of field data and the results of numerical modeling.

Results. The article demonstrates the process of tuning the unsteady operating modes of two wells with ESP in PSA mode using specialized so` ware based on real field data (multiphase flow meter, pressure gauges, etc.) taking into account the well design, ESP characteristics, additional equipment (valves, separator and etc.) and formation parameters. The model was tuned to actual data, and possible ways to optimize the operating mode were shown. In addition, the work provides an analysis of the sensitivity of fluid properties and well parameters to unsteady flow in the well.

Conclusion. The work analyzed the operation of more than 40 low-flow wells with HW and MHF with ESP in PSA mode. According to the results of the analysis, ESPs in PSA mode can effectively reduce bottomhole pressure to minimum values of 20–30 bar, provided there is a stable fluid level in the annulus. To select the optimal operating mode of the ESP in PSA mode for low-flow wells, it is recommended to use mathematical models of unsteady multiphase flow in wells.

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