Control Factors Of High Quality Reservoirs In The Deep Depression Of Bonan Sub-sag

Based on the theory of petroleum geology,this paper combined with nearly 100 of the well logging,mud logging data,core sample of retrieve the casting thin sections,scanning electron microscopy,lithological analysis,such as testing,the reservoir in the studied area the petrology characteristics,physical characteristics,reservoir space types,types and distribution characteristics of sedimentary facies,diagenesis,diagenetic environment and formation pressure characteristic and so on has carried on the comprehensive study,divided into relatively high quality reservoir,and from the sedimentation,diagenesis and reservoir pressure and so on to explore the main controlling factors of the high quality reservoirs.Study think south bonan sub-sag,deep reservoir is secondary pore development reservoir,the main development of crack,dissolution pores,intergranular micropore and fracture-pore complex pore,diagenesis dominated its physical characteristics.There is a significant positive correlation between porosity and permeability in the reservoirs in the three to the four segments of sand,but the correlation between the four segments is worse than that in the three segments of sand,reflecting the contribution of deep fractures to permeability.The early fan-delta facies and the late saline-lake facies of the four segments are characterized by the development of fan-delta facies.The three segments of sand is the heyday of braided river delta development,which is mainly distributed in the southeast of the depression.The development of gypsum stratum in the fourth section of sand controlled the early strong alkaline diagenetic environment and formed strong cementation.In the middle and late acidic environment,a large amount of cementite dissolved slowly in the early stage,and the degree of dissolution gradually increased with the passage of time,forming a secondary dissolution pore development zone below 3500 m.Under the combined action of acid-base fluid,the near hydrocarbon source rocks have better physical properties,while those far from hydrocarbon source rocks gradually deteriorate.During pyrolysis of hydrocarbon source rock,kerogen changes from solid state to liquid or gaseous oil and gas.In this process,the volume of fluid will increase.If the fluid is obstructed when it moves outward,abnormal high pressure of local fluid will be formed.At the same time,the organic acid released by hydrocarbon source rock leads to the dissolution of rock particles in the reservoir,resulting in dissolution pores,increasing porosity and expanding the exploration space of deep reservoir.Dissolution is the main cause of secondary pore development and can effectively improve the reservoir storage performance.The effectiveness of deep reservoir in bonan depression is controlled by many factors,among which sedimentary action is the foundation,diagenesis and abnormal high pressure are the key factors.