Impact of diagenesis on reservoir quality of the lacustrine mixed carbonate-siliciclastic-volcaniclastic rocks in China

The lacustrine mixed rocks, which are composed of detrital, carbonate, and volcanic materials, have increasingly attracted attention due to their association with significant oil and gas occurrences. Their complex compositions influence the diagenetic products and consequently reservoir quality. The current study critically reviews diagenesis of mixed rocks and its impact on reservoir quality, particularly the influence of volcanic components on hydrocarbon potential accumulation in lacustrine mixed rocks in China. Although there are various classifications of lithologies, the definition of the mixed rocks is mainly based on the relative contents of their constituents since the terrigenous-dominated and carbonate-dominated mixed rocks are the main types. Compaction was the major factor that negatively impacts the reservoir quality and followed by cementation particularly with dolomite due to rich contributions of Mg2+ from the alteration of volcanic constituents. On the contrary, the dissolution of feldspar, tuffaceous components and calcite cements can improve the reservoir porosity and permeability. The volcanic components are dominated by volcanic tuff, which is sourced from either the surrounding subaerial volcanic eruption or from subaqueous volcanic-hydrothermal activities. The volcanic components indirectly enhance original primary productivity, which makes mixed deposits a potential target for hydrocarbon generation and accumulation.