Distribution Characteristics Of Cenozoic Basaltic Reservoirs Of Liaohe Depression

Liaohe depression is a first-order tectonic element of Bohai Bay Basin,which is composed of six secondary-order tectonic element:Western Uplift,Western Sag,Central Uplift,Eastern Sag,Eastern Uplift and Damintun Sag.Volcanic activity was frequent in Liaohe Depression during Cenozoic,and multi-stage basalts are developed.Among them,multiple exploratory wells have obtained industrial oil gas flow.They have well oil and gas geological conditions and great exploration potential.The thesis meticulous depiction and quantitatively characterizes the basalt formation based on the data of basalt drilling core,well logging,3D seismic profile and field measured profile.Identify the development characteristics and distribution rules of different facies belts of basalt.Combined with the analysis of physical property,oil-gas bearing and heterogeneity of basalt,the distribution law of high-quality reservoir of basalt is summarized in order to provide reference for further exploration of volcanic reservoir in Liaohe Depression.1.Lithology,lithofacies division and distribution characteristics of the basalts of the Cenozoic in Liaohe DepressionLithology and lithofacies of basalt are identified and divided by using the data of drilling cores,rock debris and thin sections.There are two types of basalt in the study area,volcanic lava and pyroclastic rocks:volcanic lava include massive,vesicular?amygdaloidal?and brecciated basalts;pyroclastic rocks include basaltic breccias,basaltic agglomerates,basaltic tuffs.Four volcanic facies and nine subfacies are recognized:volcanic conduit facies?volcanic neck and hydrothermal berccias subfacies?,explosive facies?pyroclastic flow,air-fall subfacies?,effusive facies?composite flow,tabular flow and hyaloclastite subfacies?,volcanogenic sedimentary facies?epiclasts-bearing volcanogenic sediments,reworked volcanogenic sediments subfacies?.Basalts of Ef Formation are distributed in the whole area,lithofacies from less to more are volcanic conduit facies?0.56%?,effusive facies-composite flow subfacies?11.24%?,explosive facies-pyroclastic flow subfacies?21.46%?,effusive facies-composite flow subfacies?66.74%?.On the plane,lithofacies from the inside to the outside are volcanic conduit facies?explosive facies?composite flow subfacies?tabular flow subfacies;Basalts of S₃q1 Formation are distributed in Eastern Sag,lithofacies from less to more are explosive facies-air-fall subfacies?0.87%?,explosive facies-pyroclastic flow subfacies?5.39%?,effusive facies-composite lava subfacies?74.93%?,effusive facies-tabular flow subfacies?18.81%?;Basalts of S₃q2-3 Formation are distributed in Eastern Sag;Basalts of Es1 Formation are distributed in Eastern Sag,lithofacies mainly are explosive facies and effusive facies and volcanogenic sedimentary facies can be seen locally;Basalts of Ed Formation are distributed in Eastern Sag,lithofacies mainly are effusive facies.2.Quantitative characterization of basaltic reservoir unitsThe horizontal-to-vertical proportion range of 6 types of stratigraphic units?facies units?is determined by quantifying the basalt field profile.The proportional range:volcanic conduit facies-volcanic neck subfacies is 2.4-17.5;explosive facies-air-fall subfacies is 193.5-486.7;explosive facies-pyroclastic flow subfacies is 3.39-15.23;effusive facies-tabular flow and composite flow subfacie subfacies is 71.8-194;effusive facies-hyaloclastite subfacies is 5.8-8.4.The geological model of effusive facies-composite lava flow units and tabular lava flow units was established:The interior of composite lava flow units mostly are braided;The interior of tabular lava flow units mostly are layered.The range of horizontal to vertical ratio is the same as 10.39-30.8.Relationship between the thickness of flow unit and its internal vesicle zone are determined:the smaller the thickness of flow unit,the higher the proportion of pore zone.3.Development and distribution characteristics of basaltic reservoirsThe reservoir space in the south of basalt was divided into original pore?original hole and intergranular pores?,Induced porosity?intragranular dissolved pore,matrix-dissolved hole and apricot kernel dissolved hole?,primary fracture?shrinkage fracture,shattered fracture and mineral bombing fractures?and secondary fracture?dissolution fractures,hydrothermal fractures and structural seams?.Based on the analysis of physical properties and surface porosity data of basalt,it is determined that the physical properties of vesicular?amygdaloidal?basalt reservoir is the best,followed by brecciated basalt and massive basalt.Combined with the date of oil-gas-bearing,basalt reservoirs are divided into 4 categories,class?are volcanic conduit facies and explosive facies,class?are effusive facies-composite flow and hyaloclastite subfacies,class?,?are effusive facies-tabular flow and hyaloclastite subfacies and volcanogenic sedimentary facies.