Abstract: The burial depth of the Changxing Formation in Yuanba gas field,Sichuan Basin,is nearly 7 000 meters,the biological reef-shoals are small in scale and scattered in distribution,and the reservoirs are small in thickness and poor in poroperm characteristics and connectivity.In addition,the gas field has a complex gas-water contact,and high contents of hydrogen sulfide and carbon dioxide.All of these make the gas development in the study area very difficult.For effective development of the gas reservoir,a series of technologies has been innovatively integrated to finely characterize the reef-shoal reservoirs and their inter architecture.Firstly,the major factors controlling the development of favorable reservoirs are summarized and a reef-shoal development pattern is built based on study of stratigraphy,sedimentary facies,modern reef-shoal deposition and diagenesis.Secondly,under the guidance of the reef-shoal development pattern,logging interpretation and reservoir identification are performed and a forward geological model is established by integration of well-seismic data,and then the reservoir distribution is predicted through sensitive seismic attributes extraction and inversion.Thirdly,the distribution of reef-shoal reservoirs is characterized by integrating geological constraints with seismic techniques,such as profile identification,plane constraint,3D boundary delineation,and connectivity detection.Finally,the reservoir connectivity and the spatial distribution of favorable reservoirs are analyzed.Via this workflow,three structure models of reef-shoal reservoirs are established to support the production planning and well deployment in the Changxing Formation of Yuanba gas field.

Key words: fine characterization, reef-shoal reservoir, Changxing Formation, Yuanba gas field, Sichuan Basin