Study On Diagenesis And Reservoir Characteristics Of Low Permeability Sandstone Gas Reservoirs In Donghai X Area

X gas field is located in Central Inversion Structural Belt of the Xihu sag.The reservoir in the study area is characterized as low porosity,low-moderate permeability,poor physical property in general and few wells.Favorable reservoir distribution behaviors are complex and past research on this study area is not much.At present,the geological characteristics and contributing factor of the favora-ble reservoir remain unknown which results in the delay of gas production.It is critical to evaluate low permeability reservoir quality based on geological characteristics,which can help favorable reservoir distribution prediction in the near future.In this study,we did research on sedimentation in reservoir with information of core analysis,casted thin section,logging and seismic data.Integrated lithologic facies sign,logging facies sign and seismic facies sign,it can learned that this area develop braided river delta front sub-face with micro-faces like near-shore underwater distributary channel,off-shore underwater distributary channel,underwater distributary channel side edge and underwater distributary bay.Based on the sedimentary facies analysis of the deep sandstone with low permeability,we developed a quantitative characterization method of identifying diagenetic facies.The result indicates that dissolution as well as compaction are the dominant reservoir properties impactors.With the help of quantitative parameters as dissolution rate and the compaction rate,we found six diagenetic facies types: medium dissolution and medium compaction diagenetic facies,medium dissolution and medium-strong compation diagenetic facies,strong dissolution and strong compation diagenetic facies,medium-strong dissolution and strong compation diagenetic facies,mud and silts strong compation diagenetic facies and strong cementation diagenetic facies.We made well-logging diagenetic facies with the help of both BP neural network and the knowledge formed on the relation of electronic well logging sensitive parameters and quantitative dia-genesis parameters.Combining seismic inversion attributes sensitive to dissolution and compaction such as Ip,Is and Vp/Vs and seismic inversion data,we predicted seismic diagenetic facies plane distribution.The method realizes the quantitative characteriza-tion and prediction of diagenetic facies on various scales,providing a firm foundation for “desert area” of the low permeability sandstone reservoirprediction.The pore and throat of reservoir combination types vary.According to mercury injection data,thin section observation and SEM,pore structures are divided into six kinds including big-mid pore coarse throat type,mid-small pore mid throat type,mid-small pore mid-fine throat type,small pore fine throat type,small-fine pore micro-fine throat type and fine pore micro throat type,in which type?and type?are good pore structures.According to the seismic facies,lithology,stratification,compaction,cementation and dissolution to learn the controlling factors of low permeability reservoir evaluation.The reservoir can be divided into four categories,and each category summarized the genetic mechanism of the reservoir,the first of which is the best favorable reservoirs.