Comprehensive Production Evaluation for Gas Condensate at Early Exploration Stage by Using Downhole Fluid Analysis DFA and Numerical Simulation: Case Study from China Bohai Bay

Abstract The new gas condensate has been discovered recently in Bohai Bay China, and due to the complex of the fluid behaviour in nature, appropriate characterization of the in-situ fluids and relevant flow testing can provide valuable insight into gas condensate reservoir forecasting. This paper discussed a comprehensive methodology for reliable productivity evaluation with the aid of in-situ fluid characterization and interval pressure testing, and its results as a key factor not only fed into DST design and equipment optimization for better production evaluation design but also can be optimal production prediction for reserve booking. Based on the efficient and reliable productivity evaluation, we can make the real-time decision on whether to carry on DST and which DST equipment should be chosen and where to test it. However, we has been dealing with heavy oil for very long time, and the common DST equipment in Bohai Bay is not designed for condensate reservoir, but heavy oil, plus there were no published case studies in China about DST modification from heavy oil to gas condensate, and what can be done for production forecasting in gas condensate reservoir. In this paper, a new solution was proposed base on the problem elaborated above. An integrated approach was conducted to overcome challenges by using all available data from Wireline Formation Tester (WFT) and conventional log data. An accurate permeability is always the foundation of a good prediction, a single well model was built by taking full advantage of all permeability information; Compositional model is the best way to simulate the condensate phase change, in this paper, a calibrated composition was deduced by combining with semi-quantitative DFA composition and PVT analysis software (PVTi) via calibrating downhole measured GOR and density; Black oil model is the most common and popular method to evaluated single well productivity, but the uncertainty of condensate viscosity usually leads huge error, based on the calibrated composition results, evaluated the downhole fluid viscosity, after downhole fluid viscosity correctly evaluated, black oil model can also be applied in condensate productivity evaluation. DST results were used to validate the results from this approach, the error percentage range is around 10% compare with DST results. This new solution has following values: an accurate gas condensate production forecast become possible even without PVT lab results. A quick gas condensate production workflow has been set up for this field; and the methodology applied is not limited to this specific field but applicable to other fields with condensate fluid type.