Improvements in the Dehydration Process of Heavy Crude Oil, Using CFD: Case Study Campo Quifa-Colombia

Abstract

Quifa is one of the largest heavy-oil fields in Colombia with a total fluids production of 1,320 KBPD with a water cut of 96.7% through 272 active wells, approximatively. Facilities to handle such amounts of water, have to deliver crude oil under market specifications and clean up the water prior to its reinjection, require several stages of oil-water separation. The first phase in oil water separation process is Free Water Knock Out vessels (FWKO), which are in charge of extracting to extract most of the water, frequently assisted by heat or chemical products which help gravity to perform the separation. The treated water (which contain still some oil) is then directed to the following stage separation carried out by the big tanks called skimmers, which are designed to clean the water down to a few ppm of oil. Nowadays, even though the advance on computational calculations has increased, these tanks are frequently designed using only the concept of time of residence and considering the internal velocities to be as low as possible, so that improve separation. For these last considerations, FWKOs and Skimmers could have internal components like manifold or baffles. The present work explains a CFD (Computational Fluids Dynamics) study of different internal manifolds configurations, which aimed to improve the fluid distributions and velocities inside the tanks of Quifa field. Simulations were performed by CFX commercial software under two-phase flow eulerian-eulerian homogeneous model. The optimum manifold configuration, achieves uniform static pressure and flow distribution across the entire main pipe, reducing secondary internal flows and hydraulic losses. Then, CFD calculations were carried out in the whole skimmer tank, using the original manifold and the improved one. Results show an increase in the separation process, due to the new internal velocity field. Supported by the simulations results, these geometrical improvements in the internal manifolds were applied/constructed in one of the skimmer tanks in Quifa Field. Field results show an improvement on separation efficiency, going from 38% average efficiency in the original tanks (Skim-10 and Skim-30), up to 87% in the modified one (Skim-30). The quality of exit-water was reduced from 300 ppm average up to 77 ppm. The flow capacity of the skimmer 30 has been improved and can handle up to 600 KBFPD. This represents 62% more capacity than Skimmer 10, and 42% more than Skimmer 20.