ERD Multilateral well open hole junction zone stability for purpose of well construction optimization

   Introduction. As conventional hydrocarbon reservoirs become depleted during extended production the industry is increasingly focusing on the development of hard-to-recover reserves. Key technologies for their exploitation include the construction of horizontal wells and hydraulic fracturing (including multistage hydraulic fracturing, MHF). However, in the case of thin reservoir formations where MHF is complicated due to high risks of fracture breakthrough into the gas-oil contact (GOC) or underlying water zone the construction of multilateral wells becomes more relevant. This approach increases the drainage area and raises well production rates to economically viable levels. In addition to maintaining the stability of the boreholes themselves the stability of the junction zone is a critical factor for the successful well construction.

   Aim. The objective of this study was to evaluate the junction zone stability in multilateral well’s horizontal open boreholes.

   Methods. The study employed complex 3D geomechanical modeling of the stress-strain state and rock stability in two boreholes junction zone under various sidetracking parameters: the orientation of the main borehole relative to horizontal stresses; the orientation of the lateral borehole relative to the main borehole (sidetracking direction and intensity); deviation angle of the main borehole; the influence of the lateral borehole’s diameter; different mud weight and corresponding wellbore pressures above and below reservoir pressure.

   Results. Geomechanical modeling combined with drilling geomechanics support and timely recommendations allowed to adjust the planned kick-off point when the current drill bit depth approached the junction zone. This optimization ensured safer intervals (in terms of stability) for both the bridge between the wellbores and the borehole wall. The accident-free drilling and the junction zone continuous stability during subsequent production confirmed the accuracy of the conducted analysis.

   Conclusion. Complex 3D modeling of junction zone stability accounting the results of 1D modeled mechanical properties, pressures and stresses allows to optimize lateral borehole sidetracking parameters during multilateral well construction. This approach ensures both accident-free well construction and its subsequent exploitation.

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