| Unconventional gas has gradually become the mainstay of global gas production.Since the discovery of deep basin tight sandstone gas reservoirs in the San Juan Basin in the United States in 1972,more than 70 tight sandstone gas reservoirs have been discovered worldwide.China has unique geological conditions that breed extremely rich unconventional gas resources,such as tight gas.However,tight gas reservoirs are usually characterized by thin effective reservoir monolayer thickness,strong reservoir inhomogeneity as well as large longitudinal and transverse variations in physical properties and complex gas-water relationships,which make it difficult to predict the effective reservoir distribution and gas-bearing distribution by geophysical methods,which also seriously affects the exploration and development process of tight gas reservoirs.Under the current deformed energy structure of China,which relies heavily on coal,accelerating the development and utilization of unconventional natural gas resources such as tight gas is crucial to improve the energy structure of China.The Jurassic Shaximiao Formation,a sedimentary system of sand in the lake-river system of the Sichuan Basin,is currently a major focus for tight gas exploration.In 2018,gas reservoirs were uncovered and since then,15 large oil and gas reservoirs have been identified in this group,which possess promising prospects for development and research value.Among them,the formation of the Shaximiao Formation in the Qulin area is thick and has developed multiple phases of rivers in the longitudinal direction,which is widely distributed in the study area and provides good conditions for the exploration and development of tight gas.This thesis investigates the fluvial sands of the Jurassic Shaximiao Formation in Qiulin,located in the center of Sichuan.First,by analyzing known geological,logging and seismic data,based on the petrophysical analysis of the reservoir,the sensitive parameter pairs applicable to distinguish the sandy mudstone are preferably selected.Based on the existing sedimentary phase type delineation and stratigraphic architecture,a multi-well sand comparison was conducted to clarify the logging response characteristics of the riverine sand body.Then,the seismic response characteristics of the "bright" and "non-bright" sand bodies were clarified by AVO forward simulations combined with seismic profiles of consecutive wells.For the "bright" sands,a pre-stack simultaneous inversion was used to obtain the data bodies of density and longitudinal and transverse wave velocity ratios,and the sand bodies were analyzed and identified by constructing an indicator factor to extract slices along the layers.For the "non-bright" sand bodies,a combination of sensitive seismic attribute slicing and multi-attribute inversion is used to identify and finely predict the spread of the river sand bodies.Finally,the stratigraphic slices were extracted by hourly windows to display or visualize the river sand bodies in 3D to clarify the spatial distribution of river sand bodies in the Shaximiao Formation in the Qulin area,which provides more targeted guidance for later exploration and development.The results of the study show that the Shaximiao Formation in the Qulin area has developed multiple channels in the longitudinal direction,among which the main channels are mainly distributed in the three sub-sections in the lower part of the Shaji section,among which the sand groups No.8,No.14 and No.17 are characterized by Class III AVO response,and the sand group No.11 is characterized by Class I AVO response and shows "bright" sand bodies in the seismic section;the sand groups No.9,No.10 and No.12 are characterized by Class I AVO response and show "bright" sand bodies in the seismic section.The No.9,No.10,No.12,No.13,No.15,No.16 and No.18 sand groups are Type II AVO response features,and they are "non-bright" sand bodies in the seismic profile. |
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