Abstract:

The journey marching into deep and ultra-deep carbonates in China has been rewarded with more and more oil and gas discoveries, thus making the country the most active area for ultra-deep oil and gas exploration and development across the world.As a result, progresses have been made in the study of formation mechanisms, geological models, geophysical prediction and fine geo-modeling of these carbonate reservoirs.Some preliminary consensuses on high-quality deep carbonate reservoir genesis were reached: original high-energy facies and early dolomitization are the basis for the development of high-quality reservoirs; tectonic uplift activities lead to meteoric water karstification associated with unconformity, resulting in karst fractured-vuggy reservoirs; and a combination of early-stage material basis with later burial environment is key to the formation and preservation of high-quality reservoirs.Significant progress identification and tracking of diagenetic fluids and timing of diagenesis shed light on the diagenetic evolution analysis and geo-modeling with high precision and resolution.Substantial advancement has also been achieved in seismic technology for the elastic property variation trend prediction of rock frame under high temperature and high pressure, the construction of rock physics models, the elastic property variation trend prediction of multi-phase pore fluids mixtures and the high-resolution seismic inversion.As for the fine geo-modeling of the reservoirs, the multi-point statistics technology combined with sedimentary process simulation, porous carbonate sedimentary inversion with intelligent optimization, petrophysical facies modeling of multi-scale data fusion, and cellular automata fault-controlled paleokarst process numerical simulation were developed.Despite the progress, the study of deep and ultra-deep carbonate reservoirs is still faced with a series of significant theoretical and technical challenges: disputes on genesis, technical bottlenecks constraining seismic prediction, and a lack of effective and fine characterization and model for reservoirs, to name just a few.It is suggested that the future study be focused on the diagenetic fluid identification based on available petrological, mineralogical and geochemical data, as well as revealing the formation and maintenance mechanisms of reservoir space under complex fluids through high temperature and high pressure dissolution experiments and numerical modeling; on the development of a system for elastic property measurement of carbonates under higher temperature and pressure settings to analyze the scaling effects of seismic wave propragation due to the strong reservoir heterogeneities and establish the reservoir characterization workflow that can be real-timely optimized according to the geological target as well; on forward and inversion numerical simulation of sedimentary reservoirs and diagenesis under multi-field coupling; and on intelligent geo-modeling for multi-scale data fusion and multi-method collaboration with a view to improving the geo-modeling accuracy.

Key words: formation mechanism, petrophysical model, seismic prediction, fine geo-modeling, geological process simulation, geological model, carbonate reservoir, deep and ultra-deep reservoirs