Experiment Study And Application Of CO₂-Rich Fluid Interacting With Sandstone

The Xiqiao tectonic belt of Huangqiao area is located in Subei Slopes of Lower Yangtze region,under the Nanjing Depression of Yangtze Basin.Permian,from bottom to top,is composed by Qixia,Gufeng,Longtan and Dalong Formation.Lower Yangtze Huangqiao region has gone through smooth motion long before the Indo-down,Indo late-mid-Yanshan extrusion pushover,Yanshan late-early Himalayan extensional rift and late Himalayan uplift and erosion of the four tectonic stages,resulting in formation in the region repeatedly settlement-burial uplifting history feature.Through core observation,thin section,X ray diffraction analysis,electron microprobe analysis,scanning electron microscopy and energy spectrum analysis,and combined with production and research data,the characteristics of Permian Longtan reservoir,such as petrology,diagenesis,reservoir,reservoir space of oil and gas output in Huangqiao area are researched in detail,especially,the Xi 2 wells and Xi 3 wells.Huangqiao oil and gas field both has CO2 and oil and gas.The output of crude oil and CO2 between different wells is huge different,and the related sanstone reservoir is also very different.The sandstone of Longtan Formation is of strong heterogeneity and is not completely controlled by lithofacies.In the area,physical properties of the Xi 3 well and Su 174 well is the best,and taking them as the center,the physical properties of the surrounding is getting gradually worse with a strong plane heterogeneity.Xi 3 well is the main production wells and the output of CO2 is mainly about ten thousand cubic meters.Tts lithology is medium grained quartz sandstone.The dissolution phenomenon is very obvious.The feldspar is exhaustedly dissolved,and only a small amount of residual carbonate cements is remained after the dissolution.A large number of intragranular and intergranular dissolved pore is developed,and the indicative minerals-Sodium aluminum silicate,associated with the action of CO2,is found.The Xi 2 well,about one kilometer away from the Xi 3 wells,has almost no oil and gas.Tts lithology is medium grained feldspar quartz sandstone,and has more calcite,siderite content,but no dawsonite.The physical property of Xi 3 well is much better than that of Xi 2 well.The effect of CO2 is the main reason for the differences between the reservoirs of the Xi 2 well and Xi 3 well,and is also the key factor for the formation of oil and gas reservoirs.Based on the background above,the reformation of reservoir by CO2 fluid is researched under simulated formation environment of depth between 1500 m and 4000 m(temperature:60-120?,pressure:10-40 Mpa)using interaction experiments of the CO2/formation water/sandstone system in a closed container.The experimental results show that the corrosion of sandstone by C02-rich fluid is obvious,and that dissolution of minerals are mainly carbonate minerals,and the associated Ca ion concentration is more two times than other ions.The dissolution of carbonate minerals can get balance in 72 h and its dissolution rate is inversely proportional to the temperature but is proportional to the pressure.Feldspar minerals are also dissolved but very weak because it has not yet to reach balance in this experiment.Under the condition of high temperature and pressure,dissolution is the most significant,and the pressure is the decisive element,because it decides the solubility of CO2 in the solution,which controls the corrosion rate and the dissolved amount of carbonate minerals.In combination with the geological background,the mantle-derived CO2,deep major fault/fracture,reservoir,seals and other elements in this area,constitute the basis of CO2-rich fluid's reconstruction on the reservoir in the background of high temperature and high pressure.The release of mantle-derived CO2 is controlled by deep fault in Huang Qiao region.The strength of CO2 activity is obviously controlled by fault.In the fluid zone,with high temperature and high CO2 concentration,the dissolution is strong and the silicate precipitation is very obvious,as a result,reservoir improvement is very significant.In the outer zone of fluid,the temperature and CO2 concentration become low,as a result,the dissolution is weak and the reservoir physical property is very poor.This is the main reason for difference of reservoir between the Xi 3 well and Xi 2 well,also the reason for the formation of longtan reservoir of Xi 3 well.Based on this,the longtan reservoir accumulation mode in Huangqiao region is built.The reservoir is controlled by fracture.and the physical property of the reservoir is gradual horizontally and extends vertically.Physical properties of the Xi 3 well and Su 174 well is the best,and taking them as the center,the physical properties of the surrounding is getting gradually worse.