The Operator's challenge was the construction of a sub-horizontal well with 1500 m liner section in area with limited offset experience. The main development difficulty of the East Urengoy license area is the abnormally high pore pressure Achimov deposit. The widely used practice of drilling for these reservoirs with S-shaped profile wells has been utilized for a long while. However, the construction of sub-horizontal wells is still a challenge, and often accompanied by high incident rates.

Before drilling the well, all necessary fluid engineering modelling was performed. According to the hydraulic calculations, drilling of the horizontal well with traditional fluid properties was not possible due to exceeding the maximum ECD range. Multiple laboratory tests were performed to optimize the drilling fluid parameters and rheological properties with respect to ECD reduction and reducing potential for weight fluctuations due to barite sag. Based on the data obtained, recommendations were issued to predict ECD levels while drilling and tripping. At the same time, step-by-step action plans were developed for trouble-free drilling.

While utilizing this optimized fluid, with close interaction and cooperation between the project Operator (ROSPAN International), the Customer's research and development center, technical support service and the drilling contractor, the first sub-horizontal well on this licensed site has been successfully drilled.

The following main actions were developed and executed during the well construction process:

  1. Maintained the hydraulic pressure (marginally) above the pore pressure through careful fluid management.

  2. The rheological properties of the drilling fluid were maintained to the developed (lab verified) specifications.

  3. Careful hydraulic pressure management during tripping. Extensive planning of the tripping operations included increasing the mud weight before tripping to create the necessary margin and optimization of the tripping rate.

  4. Ensuring effective drilling parameters and preparing the wellbore for the casing run according to hydraulic calculations.

  5. Recommended optimized drilling fluid parameters aimed at preventing barite sag under abnormally high pore pressure and high bottom hole temperatures (up to 110 deg C).

  6. Use of specialized pills to assist prevent the loss of circulation and wellbore instability.

This article is devoted to the development of drilling fluid solutions and practical techniques for effectively drilling wells in the area with challenging formations. This case study, as well as the lessons learned will be used for ongoing drilling projects in the area.

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