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Integrated Case Study From Reservoir Characterization to Improved Well Performance Evaluation in Abnormal HPHT Tight Gas Reservoir

Abstract

Productivity evaluation of tight gas reservoir with permeability range from tight (<1 mD) to ultralow (<0.1mD) is crucial especially in deep HPHT reservoir in the South China Sea, as it contributes and feeds the key information to the later well testing plan, the completion design, reserves booking and further development plan. However, the production prediction in such tight formation with HPHT is extremely challenging and under the elevated level of uncertainty, such impact manifest in the four primary areas: (1) operational challenges to acquire the quality data; (2) the multi-controlling factors of reservoir quality; (3) the complex diagenesis and lithology for formation evaluation; (4) the various control parameters for evaluation of water and gas production and high CO2 concentration across the gas reservoir.

HPHT reservoirs became the exploration growing interest in the long-term energy planning in the South China Sea, and the case study from this ambitious exploration campaign investigated 6 wells data. Firstly, from the geological viewpoint, integrated borehole geology and mud logs and core data to understand the depositional micro-facies and sequence and analyze its impact on the reservoir properties. Secondly, formation evaluation based on the conventional and NMR logging was deployed and calibrated with core data and Wireline Formation Testing data to set up the correlations among porosity, permeability, water saturation, NMR bound fluid volume and free fluid volume. Thirdly, water saturation is further characterized utilizing NMR data and core data, and relative permeability model is set up from NMR and Park Jones equation and calibrated by core data. Lastly, integrate all the data and analysis result to build reservoir model for production prediction, and different scaled permeability from open-hole logs, wireline formation testing, and DST are utilized systematically to characterize reservoir heterogeneity.

This comprehensive case study elaborated the vital role of integration of all available data to understand the impact of the geology deposition to the formation properties, identify the controlling factors of reservoir properties, analyze the lithological impact on the formation evaluation, and eventually find out the key factors that impact well performance and predict well production in the HPHT tight gas reservoirs. Further on, the case study derives the relationship between reservoir properties, lithology, and production, and minimizes the uncertainty of well productivity evaluation. Last but not least, it provides the excellent field correlations and workflow for the further exploration activities in HPHT reservoirs in Yingge Hai Basin.