EFFECTS OF WELLHEAD PRESSURE ON FLOW VARIABLES DURING MULTI-PHASE FLOW OF WATER-OIL-GAS FROM A WELL

ABSTRACT

In oil or gas production wells, the multiphase flow usually consists of oil, gas and water. The complexity of the coproduction of these fluid phases are usually impacted by several factors such as operating conditions, well configuration, the nature of the flowing fluids, the mass transfer between the different fluid phases, phase behavior and the actual well conditions. As a way of controlling production from the case study wells, regulating the wellhead pressure has often been recommended as the general industrial practice. In order to avoid impairing the entire production system, it is usually necessary to model the well performance at different suggested wellhead pressure so as to accurately predict the flow variables of the case study well. This study uses a well model producing from a black oil reservoir with initial reservoir pressure, 3500psia and temperature, 1800F. The well is located at depth 8400ft and produced via a 2.725-in tubing. The well completion option assumes a tubing production from a cased well. The effects of wellhead (solution node) pressure on flow variables during the production of oil, water and gas from a vertical well were studied. The findings show that wellhead pressure remains an influencing parameter that can be used to optimize production from a well since it greatly affects multiphase flow variables such as phase production rates, GOR, phase flow velocity, phase densities, phase superficial velocities, the gravity and frictional pressure gradient terms and the system lifting pressure. Further analysis of first node pressure and producing GOR shows that low GOR crude oils (typical ordinary black oil) most likely will require more lifting energy and some cases, a gas lift or artificial lift. From the findings from the work, few recommendations were presented towards understanding the complex mechanism of multiphase flow in vertical wells and its corresponding influence of flow and production variables.