Displacement Mechanics and Stability of Foamy Oil during Secondary Recovery of Heavy Oil Using Methane and Air

Abstract

A pesar de que se llevaron a cabo muchas investigaciones experimentales sobre el flujo de petróleo espumoso, los fundamentos teóricos de su desempeño aún no son lo suficientemente convincentes, y los mecanismos para los procesos dinámicos y la estabilidad aún no se comprenden completamente. Con el fin de desarrollar una comprensión mecanicista del flujo de petróleo espumoso en un medio poroso, se consideraron experimentos de laboratorio bajo dos escenarios de inyección utilizando metano y aire como gases de inyección. Se realizaron experimentos de inyección en un esquema CSI de un solo pozo para comprender la generación de petróleo espumoso en reservorios post-CHOPS. Se consideró que el esquema CSI de múltiples pozos para comprender la generación de petróleo espumoso en reservorios delgados de petróleo pesado. Para ambos arreglos, se realizaron diferentes estrategias de inyección, tales como inyección alterna e inyección simultánea de gas. Se ha observado que el uso del aire ahorra el uso de metano hasta un 26 % y un 51 % en esquemas de inyección de un solo pozo y de pozos múltiple, respectivamente.

Heavy oil and extra-heavy oil (natural bitumen and oil sands) resources represent 70% of the global petroleum reserves and are mostly found in shallow reservoirs with thin pay zones formed by unconsolidated sands. Thermal recovery methods are recognized for being the most efficient; yet, these methods face environmental challenges due to the high emissions of carbon dioxide generated by high energy demands, leading to high operational costs. Therefore, non-thermal recovery methods have attracted special attention from both industry and academia. Foamy oil is the terminology commonly accepted to describe an atypical behavior associated with heavy oil flow formed as a response to pressure depletion. The cyclic solvent injection (CSI) technology is a solvent-based non-thermal process that has gained interest and is considered as an effective technique for increasing the recovery factor either as a follow-up process to the cold heavy oil production with sand (CHOPS) or for thin heavy oil reservoirs. Notwithstanding that many experimental investigations on foamy oil flow were carried out, theoretical foundations of its performance are still not convincing enough, and the mechanisms for the dynamic processes and stability continue to not be fully understood. In order to develop a mechanistic understanding of foamy oil flow in a porous medium, laboratory experiments under two different well arrangement scenarios were considered, single-well and multi-well injection schemes, using methane and air as the injection gasses. Single-well CSI scheme injection experiments were performed in order to understand, in a more representative manner, the foamy oil generation by injecting gas externally to post-CHOPS reservoirs. The multi-well CSI scheme was considered to be applied in thin heavy oil reservoirs, and post-CHOPS reservoirs. For both arrangements, different injection strategies were performed, based on alternating gas injection and simultaneous gas injection. It was observed that on a single-well injection scheme, injecting a mixture of air and methane simultaneously can help to obtain larger recovery factors per cycle than when using methane alone. On a multi-well injection scheme, it has been observed that an alternating gas injection strategy has a better performance than the simultaneous injection. Using air has been observed to save methane usage up to 26% and 51% in single-well and multi-well injection schemes, respectively. Furthermore, in order to study the efficiency of using methane, air, and their mixture to generate stable foamy oils, observational experiments were performed by means of macroscopic (naked eye) and microscopic visualization which was interpreted through foamy oil stability parameters such as time of foamability and collapse, number of gas bubbles, gas bubbles distribution, and maximum bubble size. Using a mixture of air and methane has been observed not only to expand the volume of oil by 2.5 (volume expansion caused by methane has been found to be as high as 3.0) but also to delay the defoaming process.