Characteristics And Petroleum Implications Of The Volcanic Rocks In Dongying Formation Of The Eastern Sag Of Liaohe Basin

Volcanic rocks are widespread in the Cenozoic formation of Eastern Sag， LiaoheBasin.With the improvement of exploration technology，volcanic rocks have become themain purpose of the oil and gas exploration. The volcanic rock of Shahejie Formation inEastern sag has a higher exploration degree， and has obtained industrial oil and gasreservoirs. But the research aimed at the volcanic rocks of Dongying Formation is stillless，and still has a low degree of exploration. So this article will focus on the volcanicrocks of Dongying Formation in the Eastern Sag，ascertain its geologic features，andexplore the role of Dongying Formation volcanic rocks in oil and gas accumulation.This study is based on the rock-mineral data which include drilling core and cuttings，combine with geochemistry，well logging data and3D seismic data，full use of variousanalysis data. Through Single well analysis and volcanic strata-seismic wells contrast tostudy the characteristics of volcanic rock lithology，lithofacies，vertical sequence and otherfeatures. Use core hand specimens，ordinary thin sections，casting thin sections to studythe reservoir space types of Dongying formation volcanic rock. On the basis of volcanicrock reservoir property measurement data and the conventional mercury injection data，analyse the reservoir characteristics of the volcanic rock of Dongying formation.Comprehensive analysis the factors that control the formation of volcanic rock reservoirand discuss the petroleum geologic significance of the volcanic rocks of DongyingFormation. First use the drilling cores，cuttings，slice，geochemistry and well logging data tostudy the volcanic lithology and lithofacies characteristics. According to the diageneticway and structure features，the volcanic rocks of Dongying formation in the Eastern Sagof Liaohe Basin can be divided into lava，pyroclastic rocks，sedimentary pyroclastic rocks3types，which include7kinds of lithology. The lithology is mainly basalt，followed bytrachyandesite，and they are alkali rocks, which indicate the stretching rift environment.The lithofacies of Dongying formation volcanic rock can be divided into four facies andnine subfacies. The lithofacies are mainly effusive lava flow facies，which followed byvolcanic sedimentary facies and extrusive dome facies，while volcanic conduit facies andexplosive facies less develop.On the basis of volcanic rock lithology and lithofacies，combining with the loggingcurve and3D seismic data，through single well stages division and volcanic strata-seismicwells contrast，the volcanic rocks of Dongying formation can be divided into5eruptionstages. The volcanic rocks of Dongying formation are mainly effusive lava flow faciesbasalt，post-intrusive subfacies trachyandensite can be seen in stage2and stage3，whichformed the basic-intermediate-basic eruption cycle. The volcanic eruption intensitypresent a weak-medium-strong-weak regular pattern，the largest eruption intensity occur instage3.The volcanic rocks of Dongying formation are mainly distributed in southernDapingfang，Rongxingtun，and the thickest volcanic rocks are formed at the intersection ofJiadong fault and its associated faults.According to the observation of core hand specimens，ordinary thin sections，castingthin sections, the volcanic rock reservoir space of Dongying formation can be divided intotwo major categories of primary and secondary. the primary reservoir spaces includeprimary porosity，the amygdala pore，the matrix shrinkage joint，phenocryst blast crack，the secondary reservoir spaces include phenocryst dissolution pore，matrix dissolutionpore，fillings dissolution pore，dissolution fracture，cryptoexplosion fracture and structuralfracture.The datas of measured core porosity and permeability show that the porosity of the volcanic rock reservoir of Dongying formation belongs to the high to relatively high type，while permeability belong to the low to very low type. Vesicular basalt’s reservoir propertyis better than dense ones， it has a high-relatively high porosity and a low to middlepermeability. According to the quantitative characterization of conventional mercuryinjection data for the volcanic rock pore structure of Dongying formation，the pore throatsof Dongying formation volcanic rock are mainly micropore，its sorting is poor. Porethroats connectivity and transfusion are middle on the whole. The pore structure of thevolcanic rocks of Dongying formation can be divided into I, II, III types, the I typerepresent the best reservoir property, its lithology is vesicular basalt.The volcanic rock of Dongying formation has a good quality of reservoirs，and itshighest oil-bearing grade is oil stains. The volcanic rocks that develop in themiddle-shallow layers usually have good reservoir conditions, and usually is the favorablearea of oil and gas accumulation. But the statistical result of the measured porosity andpermeability show that clastic rocks in the same formation have more advantage overvolcanic rock reservoir, so the clastic rock of Dongying formation that develops in theshallow-middle depth is the main predominate reservoir. Therefore，in the same depthrange，the comparison of reservoir properties between volcanic rock and sedimentary rockis the most important factor that determines whether volcanic rock can be reservoir or not.The reservoir property of Dongying Formation volcanic rock is poorer than theadjacent sedimentary rock，and this difference make the volcanic rock become local caprock of the sandstone reservoir and plays the role of sealing in the process of oil and gasaccumulation. According to the reservoir-cap combination relationship，the cap rock canbe divided into two categories，direct cap rock and indirect cap rock.