Differences Between Methane and Condensate Kicks - A Simulation Study

An increasing number of the new developments on the U.K. continental shelf are condensate fields. The properties of condensates are different from those of gases or oils and, consequently, the onset of a kick in a condensate field may gives rise to somewhat different surface indications and well-control problems than in the case of a gas kick that is conventionally assumed to be composed of methane. This paper investigates the differences and similarities between gas kicks and condensate 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 complementary 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 condensates are actually complex multicomponent mixtures, it seems possible to model condensate kicks reasonably well with a simple three-component model that is based on the gas/oil ratio (GOR). The principal conclusion 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 more difficult. However, for kif ks of the same size, a condensate kick will generally result in surface and shoe pressures less than those for a methane kick. Condensate kicks also should not be mow difficult to detect.