An Insight into Wax Precipitation, Deposition and Prevention Stratagem of Gas-Condensate Flow in Wellbore Region

Abstract

Unlike conventional waxy crude oil, the condensate undergoes a complex phase evolution process in high-temperature and high-pressure conditions of deep gas-condensate reservoir, which makes it more difficult to predict and prevent the wax precipitation. This study measured the component composition, physical properties and carbon number distribution of the closed sampled condensates from the wellbore region. The fluid component in wells was corrected by combining with the gas-oil ratio of the actual production data. The wellbore temperature and pressure profiles were accurately predicted using the corrected component, and the phase envelope relationship of gas-condensate flow was reasonably determined. A cold finger apparatus was designed to test the wax deposition characteristics. The main test unit consists of a completely closed high-pressure autoclave and a cold finger with a maximum 140 °C temperature-tolerant and 16000 psi pressure-tolerant ability. The wax deposition characteristics were formulated, including wax appearance temperature (WAT), critical conditions for wax deposition, wax crystal morphology, wax deposition rate. The primary mechanisms causing wax deposition in the wellbore region of deep gas-condensate reservoirs are still the thermal diffusion and molecular diffusion. A wax crystal improved wax inhibitor consisting of hydrocarbons and polymers was collected and employed. The wax crystal improved wax inhibitor showed remarkable wax prevention performance, reducing WAT by up to 80% and achieving a 90% wax inhibiting rate within the experimental measurement concentrations. These results offer insights into the wax precipitation behavior, wax deposition characteristics, and wax prevention of the condensates.