DIFFERENCES BETWEEN METHANE AND CONDENSATE KICKS - A SIMULATION STUDY

An increasing number of the new developments on the U.K. continental s helf are condensate fields. The properties of condensates are differen t from those of gases or oils and, consequently, the onset of a kick i n a condensate field may gives rise to somewhat different surface indi cations and well-control problems than in the case of a gas kick that is conventionally assumed to be composed of methane. This paper invest igates the differences and similarities between gas kicks and condensa te kicks both in water-and oil-based drilling fluids. Information on a wide range of condensate reservoir fluids has been gathered, and four representative fluids have been selected for comparison with methane. The behavior of a kick in a wellbore has been studied using two compl ementary approaches. First, the volume of a kick as it expands up the wellbore has been calculated by considering the effect of pressure and temperature changes. Second, a simplified dynamic model of a kicking well has been used to simulate the kick detection and kick-kill phases of well control in a typical deep-well configuration. Although conden sates are actually complex multicomponent mixtures, it seems possible to model condensate kicks reasonably well with a simple three-componen t model that is based on the gas/oil ratio (GOR). The principal conclu sion for safety is that failure to detect a condensate influx on entry to a well will make control of the kick when it reaches the surface m ore difficult. However, for kif ks of the same size, a condensate kick will generally result in surface and shoe pressures less than those f or a methane kick. Condensate kicks also should not be mow difficult t o detect.