Effect of Pore Size Distribution on Phase Behavior of Sour Gas andHydrocarbon Mixtures in Tight Oil Reservoirs

摘要

Carbonate reservoirs in North Caspian Sea region of Kazakhstan produce high concentrations of sour gas oracidic gas species,including H2S and CO2.Effect of sour gas components on phase behavior of hydrocarbonmixtures in these fields needs to be clarified.In addition,some of these reservoir formations are very tightwith majority of pores falling in the nanometer range.Therefore,nanoconfinement or capillary effect couldplay an important role on phase behavior during sour crude oil production and sour gas injection processes.Gas chromatography was employed to analyze the composition of a live crude oil obtained from aCaspian reservoir and a nanopore system with a pore size distribution(PSD)that is characteristic of tightcarbonate reservoirs was set up to regulate the vaporization sequence.Using a flash calculation procedurethat incorporates capillary effect,phase behavior of sour crude oil in nanoporous media was studied.Specifically,pressure and temperature(PT)diagrams,constant composition expansion(CCE),constantvolume depletion(CVD),and CVD with a critical gas saturation(CGS)were simulated and analyzed.The live crude oil has an average molecular weight of 56.12 g/mol at bubble point pressure and reservoirtemperature,containing 13.32 mol% H2S and 2.90 mol% CO2.PT diagrams showed that the bubble pointpressure of sour crude oil is much lower than crude oil analogies that use CO2 and CH4 as substitutes byfollowing the order:H2S