Gas Reservoir Reserves Utilization Study Based on Well Testing and Petrophysical Analysis: A Case Study in MH Gas Field, China

Most of China’s old gas fields are in the middle and late stages of development. The management of gas field is greatly challenged by many factors. Due to the limitations of understanding such as structure and reservoir connectivity, there is currently a lack of clear understanding of the potential, distribution, and utilization degree of remaining reserves. This paper introduces an innovated method that combines well testing and petrophysical analysis for the gas reservoir reserves utilization status. According to the pressure build-up log-log type curve, different models can be selected for the analysis of reservoir type. An integrated solution based on joint analysis of clay content estimation derived from neutron and density can be used to determine the development of interlayers, thus the vertical reservoir connectivity. The availability of remaining reserves can be determined when the well testing analysis model is optimized by the integration of core observation, multi-well petrophysical analysis and testing. A case study is presented in MH Gas Field of the PetroChina Xinjiang Oilfield Company. The sedimentary facies are braided river delta. The lithology is mainly fine siltstone, with average porosity of 21.4% and average permeability of 125.66 mD, and there is edge and bottom water in the reservoir. It was believed that there was strong heterogeneity in the reservoir, and radial composite model with improved periphery was the first option for the well testing interpretation model. However, it is discovered that partial perforation model to be the optimum well testing interpretation model because there is longitudinal connectivity between different sand bodies, after careful joint study of core and multi-well petrophysical analysis. The new model is proved by the reservoir pressure differences between different layers, and the interpretation result matches well with the testing result. The analysis shows that the existence of multi-stage deposition between wells and the heterogeneity of interlayers are the root cause of the longitudinal connection between sand bodies. Cross-well interference testing shows that well groups with good dynamic connectivity have similar reservoir development thickness, physical properties, and the less lateral heterogeneity. We discuss an integration of well testing and multi-well petrophysical analysis for the reservoir connectivity study. The reservoir vertical connection is proved by the reservoir pressure measurement, and the model turns out to be very robust. The gas reservoir reserves utilization degree can be determined when there is a good understanding of reservoir vertical connection. The analysis methodologies can also be applied to other gas fields in China.