A large number of challenging ERD wells have already been successfully drilled in the Chayvo field using stability mud weights determined by a field-specific wellbore stability model. The original wellbore stability model was based on local insitu stresses, sonic log and shale surface area based rock strength correlations; this model was calibrated and validated against field experience. A key challenge identified in drilling Chayvo multilateral ERD wells was the reduced margin between the required higher stability mud weights and the depleted formation fracture gradient, compared to the original Chayvo ERD wells. Additionally, a high quality borehole was essential for installation of the complex multilateral equipment. The challenge was to come up with a reliable method to determine rock strength along the horizontal boreholes, as data required to apply conventional methods was sparse. This provided the incentive to explore the rock physics methodology to generate synthetic sonic logs for a well-specific rock strength characterization. These synthetic logs were incorporated into the Integrated Hole Quality and Quantitative Risk Analysis (IHQ-QRA) technology to determine the optimum mud weights for Chayvo horizontal multi-lateral wells. This paper describes how this approach resulted in successfully completing the complex Chayvo field multilateral ERD wells.
In 2013, the Chayvo field drilling program marked its 10th anniversary with a new world record ERD well (measured depth 12,700 m) and by successfully drilling and completing Russia’s most complex offshore multilateral ERD well. A record-breaking well to a measured depth of 13,000m followed in 2014. Multilateral technology enables increased production from a single well by drilling one or more additional boreholes into the reservoir from the original wellbore, or mainbore.