More than 70% reserve explored in Bohai Bay, northern offshore field in China, could be categorized as heavy oil. Only relying on the conventional production process leads to both low production rate and low recovery rate. Take NB-N oil field as an example, which started production in Oct-2005. As of April 2011, there are a total of 27 development wells, with a daily oil production of 174 m3, water cut up to 77%, and recovery rate 0.2%. The oil recovery rate is 1.52% OOIP (Original Oil in Place) only, which does not meet the expectations.

To optimize the heavy oil reservoirs production, a series of comprehensive studies and field test were carried out in the Bohai field. Innovative Logging While Drilling technology was deployed to provide distance to boundary (DTB) detection ability and combined with Rotary Steerable System (RSS) technology, which enables the wellbore to be close to target roof and maximizes reservoir exposure as the result. According to the reservoir characteristics, oil recovery technology of steam stimulation with multiple fluids (SMF) by injecting steam and non-condensate gas into oil reservoirs increases production rate. The injected gas not only enlarges the influencing scope for thermal production but also reduces viscosity together with the injected heat, thus lowering the requirements for thermal production, reducing heat loss and improving the economic feasibility of thermal production.

The paper will feature the best practices of utilizing the above innovative approaches to optimize horizontal well drilling and enhance the heavy oil reservoir performance. Several key outcomes have been observed in this project:

  • Five horizontal wells were drilled with 100% NTG and lateral sections were place close to target top to minimize attic oil

  • With the SMF technology, the average single-well daily production was increased from 10-20 m3 to 50-60 m3 when cold production process was used. The effective production period lasted 300-400 days.

The successful application of innovative technologies in NB projects, has improved both oil production and recovery rate of this heavy oil reservoir. Ultimately, this has enabled the economic use of heavy oil reservoir, especially in the Bohai Bay. The author also believes this approach could be extended to the similar type reservoir as a fit-for-purpose solution.

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