Relationship between hydrocarbon migration system and reservoir formation in the 4th Block of central Junggar Basin

Key words:  hydrocarbon migration system  fault  sandstone transport layer  control function  Jurassic  Junggar Basin

Abstract:

The Jurassic reservoirs in the 4th Block of central Junggar Basin exhibit characteristics of mixed source and multi-stage filling. The hydrocarbon migration system, formed by a combination of faults and sand bodies, plays acrucial role in controlling the migration and accumulation of oil and gas. By utilizing geological, logging and seismic data, this study aims to characterize the types and distribution characteristics of this hydrocarbon migration system and elucidate the dominant hydrocarbon migration patterns and their influence on the distribution and accumulation mode of oil and gas. The research reveals that the oil source faults serving as efficient transport channels(indicated by an evaluation coefficient of fault transport effectiveness less than 3.5 and a fault opening and closing coefficient greater than 1)act as vertical migration pathways, connecting the source rock with the reservoir. Partially and completely connected sand bodies, with a sand-ground ratio greater than 30 %, function as lateral migration channels for oil and gas. The predominant hydrocarbon migration system include the T-type fault-sand combination pattern and the staircase-type fault-sand combination pattern. In these patterns, the convergence surface of robust transmission faults aligns with the ridge of connected sand body structures, which controls the distribution of oil and gas reserves. The comprehensive evolution of migration system and the hydrocarbon charging process establish a model for reservoir formation, encompassing mixed sourcing hydrocarbon supply, a two-stage filling process, and fault-sand composite transmission and conduction. The fault and sand bodies jointly transpor hydrocarbons during the initial phase of formation, while in the subsequent phase, the fault takes on the primary role as the transport channel.