Evaluation on the prediction method of Z-factor of gas condensate with water vapor in Yacheng Gasfield

Z-factor of natural gas is one important parameter for gas reservoir engineering calculation, and it is mostly calculated by means of empirical formula.Different calculation methods are different in application range and precision, and the effect of water vapor is usually neglected in the conventional methods used for calculating Z-factor of gas condensate, so the calculation error of Z-factor is larger.In this paper, different calculation methods were adopted respectively to deal with these difficulties.Then, Z-factor of gas condensate with water vapor was calculated by using correction models (e.g.WA and Casey).Finally, the calculated Z-factor was compared with the measured value, and the applicability of three models (i.e., HY, DBR and DAK) to calculate Z-factor of gas condensate with water vapor was evaluated.It is indicated that when Z-factor of gas condensate with water vapor is calculated, the error of Z-factor which is corrected by the correction model is much smaller.The precision of three methods (i.e., HY, DBR and DAK) varies with the value ofreduced pressure (p_r).Their calculation precision is similar while 0≤p_r≤3.87.The calculation precision of HY and DAK is higher while 4.84≤p_r≤6.56.And the calculation precision of DAK is much higher while 3.87≤p_r≤4.84 and 6.56≤p_r≤7.59.