The Study On Phase Transition And Wax Precipitation Of Condensate Gas Reservoirs In Bozi Block

The study of wax deposition in condensate gas reservoir is one of the problems in the exploitation of high temperature and high pressure deep condensate gas reservoirs in China.Due to the large difference between the condensate gas reservoir formation and the ground temperature and pressure conditions,wax plugging phenomenon often occurs,accompanied by problems such as sand plugging and hydrate reverse osmosis water lock,which leads to a significant drop in oil and gas production and even stop production.The Bozi block of the Tarim Oilfield is a typical tight sand condensate gas reservoir with serious wax plugging.So it is necessary to study the phase behavior and the wax deposition pattern of well fluids in Bozi gas reservoir,which will provide the phase enveloping diagram of the condensate gas and then help to control the paraffin deposition.In this study,the PVT tester and the self-designed microscopic solid deposition tester are used to get the phase enveloping line of the condensate gas.Such testing methods allow us to monitor phase changes of “gas-liquid-solid” system at different temperatures and pressures.In addition,the real reservoir conditions can be fully simulated with visibility.The result shows that the phase behaviors of the wax-containing condensate gas is extremely complex.Under different temperature and pressure,gas phase,gas-liquid,gas-solid,and gas-liquid-solid multiphase appear respectively.The main wax components of Bozi 104 well are C16?C30,and their content is 0.111% mol per unit mole of condensate gas.The wax precipitation temperature of condensate oil is 15.4?,the maximum instantaneous wax deposition volume is 0.2258% per unit mass of condensate oil,and its cu-mulative volume is9.49% per unit mass of condensate oil.When the pressure is above the dew point,the solid wax is not dominated by the condensate oil but by long plate-like coarse wax crystals.When the pressure is below the dew point,the solid wax is condensed from thegas.The wax is soluble to the condensate oil.Then they form a transparent colloidal,glassy block material,which has a strong binding effect on the condensate oil.