Physical Model Study of Inverted Seven-spot Steamfloods In a Pool Containing Conventional Heavy Oil

Abstract

Abstract A triangular model was fabricated, containing an injection and a production well and representing one twelfth of an inverted seven-spotflood pattern, and several parameters significant to oil recovery by steam-flooding were scaled in the model size. The model was designed to simulate steam-flooding of a prototype reservoir in Alberta in which conventional heavy oil is underlain by bottom water at several places. In this physical model study, the roles of different operating variables and production strategies are examined/or regions without bottom water. The operation of the physical model provided certain insights into the, mechanism of the steam displacement process which might not otherwise have been possible. It was seen that although the temperature profiles for the steam zone grow more or less radially, the hot condensate zone ahead of the steam zone exhibits severe fingering and channelling, which results in early water breakthrough. The steam zone does not exhibit fingering. The water-oil ratio thus rises steeply in the early periods of the steamflood and then stabilizes and grows very gradually. The steam displacement is characterized by severe gravity override and under running of hot condensate fluid. The additional recovery of oil by steam flooding over water flooding is largely due to a better sweep. Of various production strategies examined with the physical model, pressure cycling' gave maximum advantage in the recovery of heavy oils. Finally, water flooding following the termination of steam injection was found to recover as much as 5 per cent additional oil from the model. Introduction Recovery of Lloydminster-type heavy oils of Alberta has been suggested as a short-range solution for meeting the growing demand for crude oil in Canada. Steam drive is one of the promising methods of achieving this objective. For this study, an oil pool in the eastern part of Alberta was chosen as the prototype. The pool has conventional heavy oil underlain by bottom water at several places. This work deals with the role of different operating variables and strategies in oil recovery from the regions in the prototype where the bottom water is absent. The objectives of this model study were to obtain insights into the manner of steam propagation, and to examine the role of flooding and steam quality. Based on a variety of considerations it was decided to use a physical model to fulfill the above objectives. The considerations leading to the choice of the particular physical model system are described below. Modelling Models (both numerical and physical) are aids to improved conceptual understanding of one or more physical processes. If various phenomena associated with a given process are adequately understood, so much so that one could write equations and assign numerical values to individual parameters, it would be prudent to work with numerical models alone, as they are much faster. One could then apply the results directly to the field. However, if certain phenomena of importance are not properly understood, physical models may help to improve the understanding of relevant facets of the process.