Prediction of wax precipitation temperature in petroleum reservoirs upon methane injection

Solid precipitation from crude oils is a major problem faced by the petroleum industry during depletion from reservoirs. The precipitating solids could be waxes which are the high molecular weight components of the crude oil. Injecting gas into an oil reservoir can improve the recovery through maintaining the reservoir pressure, displacing oil, or vaporizing the intermediate fractions of oil. The reservoir oil in contact with gas tends to get enriched in very heavy fractions that may precipitate as wax under some operative conditions. One of the ways to mitigate the problem is to have a model that can predict the conditions under which the precipitation occurs.In this work, forward and backward multiple contacts are considered to simulate the methane injection to the reservoir oils. Equilibrated compositions of the oil samples and the injected methane are computed by material balance and flash calculations. A modified multisolid-wax model is used to study the effect of mixture compositions on the wax appearance temperature (WAT). The vapor and liquid phases are described using the Peng–Robinson equation of state (PR EOS). It is shown that composition variations of the oil upon methane injection have enormous effect on the WAT.

► The WAT is lower in forward contact in comparison with the backward contact.
► In the backward contact, the WAT increases with increasing contact number.
► In multiple contact, the WAT depends on the composition of the plus fraction.