致密砾岩油藏CO2驱井筒蜡堵机理与防治对策OA

To address the frequent wax deposition issues in wellbores,caused by lower water cut(≤10%)and higher CO2 content in the produced fluid,during CO2 flooding development of tight conglomerate reservoirs in the Upper Wuerhe Formation of Mahu 1 well area,Mahu Sag,single-stage flash and constant composition expansion experiments on live oil were conducted.Gas chromatography,differential scanning calorimetry,and polarized light microscopy were employed to characterize the composition of sediments,and wax and asphaltene deposition envelopes with different CO2 contents were plotted.A four-stage flash experimental apparatus was set up to reproduce the temperature and pressure variation path in the wellbore,obtaining phase behavior and deposition data for the live oil injected with CO2 at different wellbore positions.Finally,a one-dimensional wellbore wax deposition simulation framework was constructed by tight coupling among"bulk phase behavior model,a wellbore wax deposition model,and a physical property&heat transfer model,"enabling the simulation of spatiotemporal evolution of pressure,temperature,flow regime,and wax layer thickness.The results show that the deposits consist of an nC27-nC35 microcrystalline wax skeleton cemented with asphaltenes,and that deposition is jointly driven by gas stripping extraction and Joule-Thomson cooling.CO2 dissolution elevates the bubble-point pressure and shifts the wax deposition envelope(WDE)toward higher pressures.Deposition is strongly concentrated in the shallow section(0 to 1 000 m as high risk area,with a peak around 400 m),and when mole fraction of CO2 in produced gas climbs to 50%from zero,the maximum wellhead deposition thickness increases by more than fivefold.Furthermore,when CO2 mole fraction exceeds approximately 30%,the risk of deposition grows exponentially.Based on these findings,segmented and targeted control for the 0 to 1 000 m shallow interval and CO2 mole fraction-based threshold early warning method are proposed to support flow assurance and stable production during CO2 flooding.