Reservoir Distribution Regulation Of Haerjiawu And Kalagang Formation In Santanghu Basin

The analysis and conclusion of the lithology,lithofacies,reservoir characteristics and the controlling factors of high-quality reservoirs of Carboniferous volcanic rocks in Malang Sag,Santanghu Basin are based on core photographs,casting thin sections,logging and laboratory analysis.Meanwhile,the distribution of Carboniferous volcanic reservoirs is evaluated and predicted.The main achievements are as follows:?1?The Carboniferous volcanic rocks in Santanghu Basin can be divided into intermediate-basic volcanic lava and pyroclastic rocks,which can be subdivided into 14types.The eruption pattern is mainly Hawaiian eruption,supplemented by Steboli eruption.The volcanic activity is frequently,and the Haerjiawu Formation is underwater or land-sea transition eruption pattern,and the Kalagang Formation is onshore eruption.The facies can be divided into three main types:explosive facies,overflow facies and volcanic sedimentary facies.?2?The Kalagang Formation in Malang Sag of Santanghu basin can be divided into two cycles,C₂k¹and C₂k²,and five stages,and the Haerjiawu Formation can be divided into two cycles,C₂h¹and C₂h².The cycles and stages have some inheritance in plane and profile.Three main volcanic mechanism groups are developed in the northwest,central and southern parts of Malang Sag separately,among which the volcanic mechanism of Niudong structural belt in the central part has the greatest influence on reservoirs.?3?Reservoir space types are diverse and reservoir heterogeneity is very strong.According to mercury injection curve analysis,pore throat structure in the study area can be divided into four types,most of which have low porosity and permeability or ultra-low porosity and permeability characteristics.Reservoir properties are strongly influenced by lithology,weathering leaching,dissolution and tectonism,while burial compaction has little influence on volcanic lava.?4?According to the main controls of reservoir properties,the reservoirs can be divided into 3 types,weathering-leaching reservoir,vesicular-almond reservoir and near-source dissolution reservoir.The lower limit of properties is determined by the relationship between pore and permeability and oil-bearing property.The reservoir quality can be divided into ?,? and ? grades.Weathering-leaching reservoirs are mainly distributed in the north of Malang Sag and east Niudong structural belt,and develop along the NW-SE faults.Vesicular-almond reservoirs are mostly distributed in the section of Niudong 109-Ma 36-Ma 38-Niudong 201 wells area,mainly located in the areas with the most developed overflow facies at the top of each stage and cycle.Near-source dissolution reservoirs are mainly distributed in Ma 67H well area and Ma71-Ma 33-Ma 39 wells area,mostly located in the lower part of the thick source rocks of the Haerjiawu Formation,the inner interbeds of the source rocks or the bottom of the Kalagang Formation.