Oil Recovery Mechanisms in Bitumen-Bearing Carbonate Rocks

Abstract

Abstract Bitumen-bearing carbonate reservoirs, dominated by the 406 billion barrel resource in the Grosmont formation, will provide billions of barrels of recoverable oil for the Province of Alberta. A small contribution to this development was an extensive series of initial laboratory experiments that were conducted for multiple producers under a variety of conditions. The experiments include measuring oil recovery to varying water and steam processes, both separately and in combination with each other. Displacement procedures included both washing/soaking and direct floods with temperatures ranging up to 260°C. These laboratory tests were conducted over a six year period. As this research was conducted across several producers independently, a planned statistical design was not addressed through this process. Rather, the experiments are exploratory in nature, examining the primary recovery mechanisms contributing to production performance and ultimate recovery of bitumen in these heterogeneous systems. It has been shown that bitumen can be readily recovered from fractured and connected open porosity that is accessible to steam through a gravity drainage process. Furthermore, carbonates at elevated temperatures become more water wet, and water imbibition can play a significant role in accessing recovery from the oil-bearing rock matrix. The impact of imbibition is significant, and wet steam proves a much more efficient displacing medium than dry steam. The recovery of oil from lab-scale models also shows a significant impact of thermal expansion and gas drive, which can lead to significant oil displacements at early times, particularly in areas where the localized open porosity network is extensive. Bitumen recovery from carbonate systems is achieved through a combination of these processes: thermal expansion, gas drive, gravity drainage of oil out of connected open porosity, and imbibition of water into the rock matrix.