Study on the Hydrocarbon Accumulation Model of Conventional and Unconventional Reservoirs in the Middle-Upper Permian Full Oil and Gas System, Chaiwopu Sag, Southern Junggar Basin

Abstract: Based on integrated analyses of source rock characteristics, sedimentary system evolution, reservoir properties of both conventional and unconventional units, and dynamic source-reservoir relationships, this study conducts a detailed investigation of the Permian petroleum system in the Chaiwopu Sag.

The principal findings are as follows: (1) The study area features a lacustrine depositional system within a sag setting. Large-scale, high-quality source rocks are present in the Lucaogou Formation. Both conventional and unconventional clastic reservoirs are distributed adjacent to stratigraphically above and below these source rocks, forming multiple sets of reservoir assemblages with diverse characteristics. (2) The Permian succession in the Chaiwopu Sag exhibits favorable geological conditions for a full oil and gas system. Laterally, shale oil, tight oil, and conventional glutenite reservoirs are distributed sequentially from the sag center to its margins. Vertically, surrounding the high-quality source rocks of the Lucaogou Formation, tight oil, shale oil, and conventional glutenite reservoirs occur in an ascending progression. This spatial configuration illustrates the characteristic hydrocarbon accumulation pattern of a “full oil and gas system.”

(3) Guided by this model, exploration breakthroughs have been achieved in all three reservoir types, establishing an essentially sag-wide hydrocarbon-bearing pattern. This pattern is characterized by the orderly coexistence and coupled stacking of multi-layered, multi-type reservoirs in close association with their source rocks. The establishment of this accumulation model contributes to the theory of full oil and gas systems and provides significant guidance for the exploration and development of analogous hydrocarbon-rich sags.

Keywords: full oil and gas system; orderly coexistence; accumulation model; Middle-Upper Permian; Chaiwopu Sag