The paper presents field observations for wax deposition in a North Sea reservoir. Wax deposition was observed in two wells while no wax deposition was seen in other wells in the same field. To understand the underlying mechanisms 18 different production scenarios were simulated using a fully compositional wax deposition simulator. The wax deposition was modeled as a molecular diffusion process taking into account the effects of flow regime, adiabatic expansion, solubility effects and heat exchange with the surroundings. The fluid model was configured to match the measured wax appearance temperature and wax content data for the fluid flowing. The simulated pressure and temperature profiles in the well were validated against PLT data to ensure an optimum starting point for the study. The 18 production scenarios had varying GORs, water cuts and oil production rates. The simulations allowed conclusions to be drawn about the influence of GOR, flow rate and water cut on wax deposition. The two wells with deposition were flowing at lower rate than the wells with no deposition and this was found to be the main reason for the wax deposition in those two wells. At optimum operating conditions it is possible to suppress the wax deposition whereas wax at other conditions is deposited in an amount that eventually might cause plugging of the wells.
Modeling of wax deposition has been widely used for subsea pipelines (1, 2). A wax deposition model, which has previously been applied to model wax deposition in subsea pipelines (3, 4) is in this study applied to wells at steady state conditions and used to evaluate the effect of changing operating conditions. The investigated wells are in the Valdemar field located offshore in the Danish part of the North Sea. The Valdemar field was developed using unmanned STAR platforms. Executing any coil tubing intervention requires support from a rig. That makes a coil tubing operation difficult to plan and expensive. Two wells in the field have already been plugged with wax at the surface. A wax management plan has been put in place where all wells at risk will be cleaned up every three years. The targets of this study are to find out how changes in GOR, water cut and oil production rate will affect the wax precipitation and deposition. It is further to be investigated whether the observed differences in wax deposition in the wells in the Valdemar field can be explained by operational differences or the only possible explanation is variations in wax content in the liquid produced by the various wells.
