Foam Flow Modelling for UBD Applications

摘要

While naturally occurring foaming crude oils can present unwanted operating problems in production facilities, specially created loams have been used for a variety of applications in the petroleum industry for many years. These include, but arc not limited to, foam drilling fluids, foam stimulation fluids, and foams used for controlling the mobility of various other fluids and solids. More recently, interest in the properties and behaviour of foams has increased significantly due to the use of foam drilling fluids in underbalanced drilling (UBD). In UBD, the botlomhole pressure is intentionally maintained lower than the reservoir pressure during the drilling operations. This underbalanced state is usually achieved by using a gas-liquid mixture in place of traditional (and much heavier) drilling mud. The combination of low density (i.e., low pressure loss due to hydrostatic head) and high viscosity (i.e., good capacity for cuttings transport) makes foam a strong candidate as a UBD drilling fluid. Because of the technical complexity of UBD, the success of such operations can depend on the accuracy of a detailed engineering analysis that is typically carried out both before and during the actual drilling. Accurate computer modelling of the hydraulics of flow in the drill string, the bottomhole assembly (BHA), and the return annulus is a critical component of this design and performance analysis process. When foam is used as Ihe drilling fluid, this generally means that complex questions of foam rheology and flow behaviour must be answered using technology which is simple and can be applied with relatively limited measured data.