A Physical Model to Assess Sand Production Processes during Cold Heavy Oil Production with Sand
Cold heavy oil production with sand (CHOPS) is a relatively low-cost primary production method that has been used to produce heavy oil from reservoirs since the 1990s. CHOPS is defined by the mobilization and production of reservoir sand, resulting in the development of highly porous and permeable voids (“wormholes”), which serve as conduits that facilitate heavy oil flow within the reservoir. CHOPS can produce recovery factors of up to 20%, compared to 5% for cold heavy oil production without sand. Despite the increased recovery achieved using CHOPS, 80% of the oil remaining in place is an attractive target for recovery using post-CHOPS enhanced recovery methods. Effective implementation of post-CHOPS techniques requires a better understanding of the reservoir, such as the geometry of wormholes created during CHOPS. Despite extensive field, numerical and laboratory (physical modeling) research of sand production, the factors that control wormhole geometry are still poorly understood. This thesis describes the design, construction, and commissioning of an experimental apparatus that is being used to model wormhole development. The experimental apparatus was designed to circulate fluid radially through a 15 cm thick cylindrically shaped sand pack into a fully perforated wellbore placed at the center of the sand pack. Circulation of fluid was completed through a series of tanks, valves, pipes, and a pump which was operated remotely through a computer network system. A removable porous plug was placed in the wellbore within the sand pack to control the production of sand particles, hence the apparatus allowed fluid flow either with or without sand production at different stages of each experiment. The entire assembly was designed to withstand the harsh hypergravity environment and to be operated completely remotely. A total of five commissioning tests and three experiments were completed with the apparatus. Key results of commissioning tests and a detailed analysis of the experiments are presented within this thesis. The analysis of results highlight the influence of gravitation and seepage forces in the development of void geometry within the sand pack and compare some aspects of the experimental results to simulation results obtained using the axisymmetric option of RocScience’s finite element code RS2. The experimental results are also compared to simulation results to show enhancements made to the experimental apparatus compared to previous centrifuge experiments; a notable example being the use of a gravel-filled annulus at the outermost (radial) boundary of the sand pack, which allowed the apparatus to better approximate true radial flow conditions. At the end of each experiment the apparatus was disassembled and the sand pack was analyzed. In all three experiments a cavity formed around the wellbore and took the shape of an inverted frustum. In two of the experiments multiple elongated channels extended outward from the top of the cavity linearly towards the inner boundary of the experimental container. As such, the results demonstrate the effectiveness of the new experimental apparatus to physically model two different types of cavity geometries during CHOPS operations. Recommendations are given for future improvements to be made in follow-up research; for example, to prevent premature plugging of the flow system, hence enabling longer-term sand production and the development of larger cavities.
CHOPS, Wormhole, Heavy Oil, Sand Production, Geotechnical Centrifuge
Master of Science (M.Sc.)
Civil and Geological Engineering