Diagenesis Of Volcaniclastic Rocks And Its Effect On Evolution Of Reservoir Porosity

Lujiapu depression has the most abundant oil and gas resources around Liaohe exploratory area.With the development of petroleum exploration in volcanic rocks,many key geological problems of volcaniclastic reservoir evaluation and distribution need further study.Based on the study of drilling core data of 18 wells in Lujiapu depression,the comprehensive description and quantitative characterization of volcaniclastic reservoirs are carried out in terms of lithology,lithofacies,diagenesis and reservoir space.Through the identification and division of lithology and lithofacies of volcaniclastic reservoirs,a classification system of lithology and lithofacies of volcaniclastic rocks for reservoir research needs is established.Based on the analysis of diagenesis types and stages,the reservoir space types,genesis and development characteristics are summarized,and the pore evolution process of volcaniclastic rocks is explored;On this basis,the identification criteria of high quality volcaniclastic reservoirs are established,and the formation mechanism,main controlling factors and distribution rules of volcaniclastic reservoirs are summarized.The results show that:(1)The lower Cretaceous volcaniclastic rocks in Lujiapu depression are mainly composed of 5 kinds of volcaniclastic,5 kinds of clastic particles cementation type,6 lithologies and 3 subclasses of ordinary volcaniclastic rocks,sedimentary pyroclastic rocks and pyroclastic sedimentary rocks(2)There are 9 diagenesis and 6 reservoir space types of volcaniclastic reservoirs in the study area.(3)The pore evolution of volcanic clastic rocks mainly undergoes three stages: early condensation and compaction consolidation? fluid hydrothermal filling? debris particle and matrix dissolution,forming effective reservoir spaces such as intergranular-intragranular dissolution pore,dissolution fracture and structural fracture.(4)Based on physical property data,plane porosity analysis data and hydrocarbon potential level data of logging,the reservoir properties of pyroclastic rocks are small volcaniclastic rocks > volcanic breccia > volcanic agglomerate,the reservoir properties of small volcaniclastic rocks are volcanic tuff > sedimentary tuff > tuff sandstone.(5)The 5 factors of volcaniclastic reservoir including types of cement,tectonics,fluids,dissolution and content of clay minerals.(6)The distribution pattern of high-quality volcaniclastic reservoir:(1)In the plane,it is located in the near Crater facies zone(2)In vertical,under the top boundary of volcaniclastic rock strata(3)In the micro-scope,there are more effective voids in the matrix than clastic particles,more dissolution at the edge of clastic particles(crystal debris,lithic debris and breccia)than in the interior,and more dissolution of crystal debris(feldspar)than in the debris.