Study On Wax Appearance Characteristics And Wax Deposition Behavior In Waxy Condensates

Same as conventional waxy crude oil,waxy condensates face the risk of flow assurance in reservoir,wellbore,pipeline and other surface facilities.There are different wax appearance characteristics and wax deposition behaviors in the process of exploitation and transportation,which brings many challenges to production and management.Compared with conventional waxy crude oil,the description of wax appearance and wax deposition in the exploitation and transportation of condensates has not yet formed a unified understanding.Therefore,this paper focuses on the efficient development of high-pressure condensate gas reservoir and the operation of supporting surface facilities.Based on the engineering background of condensates production in Tarim Oilfield,the physical properties,the wax appearance characteristics,the wax melting characteristics and the carbon number distribution of condensate oil were experimental analyzed.Combined with production static and dynamic data,the temperature and pressure in different depth of wells were simulated.The phase evolution process under exploitation and transportation conditions was studied.The thermodynamic model of wax appearance of waxy condensates was established.Based on the cold finger experiment,the critical conditions of wax deposition of waxy condensates were measured.Simultaneously,the rate of wax deposition and the effects of it were studied.This study show that the carbon number distribution of condensate oil is mainly C7+,accounting for 95.00%.The wax crystals are typically characterized by small needle shape.With the gradual decrease of temperature,these structures are mosaic and accumulation conditions.And then,the wax crystals continue to grow and nucleate.For the same condensate oil,the wax appearance temperature decreases with the increase of cooling rate,and the wax melting temperature increases with the increase of heating rate.For the wellbore,with the fluid production increases,the rate of temperature reduction decreases and the rate of pressure reduction increases.With the gas-oil ratio increases,the rate of temperature reduction and the rate of pressure reduction increase.In the process of well fluids lifting,the rate of temperature reduction increases,and the rate of pressure reduction along the well is relatively constant,and the slope of the pressure in different depth does not change significantly.The temperature and pressure distribution at the wellhead are the working conditions for the gasliquid two phase equilibrium conversion of waxy condensates.Surface facilities such as wellhead separators and gathering lines may have the risk of wax appearance and wax deposition.Aiming at the limitation of comprehensive and reliable description in phase evolution by commercial software and experiment,an improved PR equation of state was proposed based on Daridon equation.Therefore,the thermodynamic model of wax appearance in waxy condensates was established.And then,the calculation program was compiled with the corresponding model,which can accurately describe the phase enveloping diagram of waxy condensates.Comparing the calculated results with the software prediction results corrected by experimental data,the average deviation of the wax evolution curve and dew point was less than 10%.The temperature difference between oil and wall is the key factor of wax deposition in waxy condensate oil.Under the pressure of surface transportation,with the increase of temperature difference,the critical temperature of wax deposition increases.Besides,when the temperature difference is small,the condensate oil temperature is the main factor for wax deposition behavior.When the temperature difference is large,the temperature difference has the greatest impact on the wax deposition rate.When the condensate oil is laminar flow,the wax deposition rate is not affected by the flow rate.The research explained the mechanism of phase evolution in waxy condensates.And then,the research provides reference and scientific method,which can guide the design and optimal operation for the production and transportation of waxy condensates.