Effect Of Supercritical CO₂ Huff And Puff On Fluid/Rock Of Sandstone And Conglomerate Reservoir

Supercritical CO2 throughput is one of the most effective methods to improve the recovery of low permeability,extra low permeability,ultra low permeability and tight reservoirs.However,CO2 is a kind of highly active gas,and it easily interacts with formation water,crude oil and rock after entering the reservoir.On the one hand,the action of CO2 and formation water and rock minerals in the reservoir can change the physical properties of the reservoir.On the other hand,CO2 dissolves in the crude oil to expand the volume of the crude oil,reduce the viscosity of the crude oil,and extract the light components in the crude oil.In particular,the composition of minerals in glutenite is more complicated than that of sandstone.If CO2 interacts with formation water and rock minerals in the reservoir,it will affect the role of CO2 and crude oil in the formation,thereby reducing CO2 throughput and enhancing oil recovery.In particular,the composition of minerals in glutenite is more complicated than that of sandstone.If CO2 interacts with formation water and rock minerals in the reservoir,it will affect the role of CO2 and crude oil in the formation,thereby reducing CO2 throughput and enhancing oil recovery.Therefore,exploring the interaction between CO2 in glutenite reservoirs and formation water,rock minerals and crude oil in oil reservoirs is of great significance for studying supercritical CO2 throughput and enhancing oil recovery in glutenite reservoirs.Firstly,XRD and SEM were used to analyze the glutenite minerals,and the main rock-forming minerals and clay minerals composed of glutenite were obtained as feldspar,calcite,illite,chlorite and kaolinite.The interaction of supercritical CO2 with five single minerals composed of glutenite and the interaction of supercritical CO2 with five minerals under formation water conditions were studied at a temperature of 70? and a pressure of 20MPa.XRD,scanning electron microscopy and energy spectrum analysis of the minerals before and after the reaction showed that supercritical CO2 did not chemically interact with the five minerals that make up the glutenite under dry conditions,but physical effects occurred.It is shown that the entry of CO2 into the mineral makes the spacing of the mineral lattice layer increase,so that the characteristic peak intensity of the mineral XRD test results before and after the reaction decreases,and the degree of reduction is:calcite>illite>feldspar>kaolinite>chlorite.Under the condition of formation water,supercritical CO2 reacted strongly with five minerals.Supercritical CO2 reacted with water to form carbonic acid.Carbonic acid ionized H and reacted with five minerals.Before and after the reaction,obvious dissolution occurred on the mineral surface,and the total ion concentration in formation water increased nearly double.According to the analysis,the relationship between supercritical CO2 and five minerals is:calcite>illite>feldspar>kaolinite>chlorite.It can be seen that supercritical CO2 and minerals in glutenite consume CO2,which may affect its interaction with crude oil in glutenite reservoirs.At the same time,the effects of supercritical CO2 stimulation on the physical properties of the reservoir were studied.The five minerals were made into indoor artificial core according to the proportion of glutenite minerals.The supercritical CO2 throughput saturated distilled water/stratigraphic water core was carried out at 70? and 20MPa,and the water-phase permeability and porosity of the core before and after the throughput were compared and analyzed.It was found that the core properties of the core were deteriorated after the supercritical CO2 was swallowed.According to the analysis,Ca2+in the formation water is the main factor leading to the deterioration of core properties after puffing.Finally,the effect of enhanced oil recovery by supercritical CO2 huff and puff is studied.Through supercritical CO2 huff and puff saturated oil/saturated oil with irreducible water core experiment,comparing the oil components and crude oil recovery under the two conditions,it is found that with the increase of soaking time,the heavy component content of produced oil increases gradually.The existence of irreducible water weakens the extraction efficiency of supercritical CO2 for crude oil,makes the oil produced relatively lighter in the later stage,and reduces the oil recovery,which affects the role of CO2 and crude oil.Therefore,the interaction of supercritical CO2 with rock minerals and formation water in sandy conglomerate reservoirs will weaken the interaction between CO2 and crude oil,and the degree of its influence is one of the key factors for the success of supercritical CO2 huff and puff in enhancing oil recovery.