An Evaluation of Enhanced Oil Recovery Strategies for Extra Heavy Oil Reservoir after Cold Production without Sand in Orinoco, Venezuela

Abstract

The Orinoco heavy oil belt in Venezuela is one of the largest extra-heavy oil resources in the world. It has become a major goal for the unconventional oil exploitation in these years. Now, the most common production method is to use the horizontal well cold production without sand. It is an economic and commercial process, and with the reservoir of this area have high initial gas to oil ratio (GOR), porosity and permeability with unconsolidated sand. However, after several years' production, the oil rate draws down quickly caused by the reservoir pressure drops; the key challenge of cold production is that the recovery factor (RF) tends to be only between 8% and 12%, implying that the majority of the oil remains in the oil formation. It is necessary to develop viable recovery processes as a follow-up process for cold production. Generally, steam based recovery method was widely used as a follow-up process for cold production. In this paper, steam fracturing (dilation) Cyclic Steam Stimulation (CSS) operation and Non steam fracturing (No dilation) CSS operation by using reservoir simulator is examined for a post cold production in extra heavy oil reservoir, in order to analyze the performance of the oil rate, cumulative steam-to-oil ratio (cSOR), steam depletion zone, greenhouse gas emission and some necessary parameters. The key component of the steam fracturing (dilation) is the ability to inject high temperature and pressure steam into the formation to fracture the reservoir rock which in turn raises the rock permeability and mobilized the oil by lowering the visocisity. To compare the results of the dilation and no dilation CSS operation, this study reveal that due to the steam is injected into the reservoir by using the same cumulative cold water equivalent (CWE), the steam condensate; pressurized by steam vapour, fracture the formation. Dilation operation achieves higher oil rate, lower cSOR. The result also show that fraturing (dilation) of the reservoir during steam injection relieves the pressure which in turn lowers the steam injection pressure below the case where No dilation operation ouccurs.

Conversion Timing of Following-Up Thermal Recovery Approaches of Post-CHOP for Foamy Extraheavy Oil Reservoirs

“…However, for the foamy extraheavy oil reservoirs located in Orinoco Heavy Oil Belt at Venezuela, the cold heavy oil production (CHOP) method was applied in the initial stage of oilfield production using horizontal wells. Due to the mobility of the foamy oil flow, the CHOP method received unexpected success regardless of the high viscosity [13][14][15].…”

“…However, the studies of thermal recovery techniques after CHOP stage in foamy extraheavy oil reservoirs are relatively few. Bao et al [14] performed the numerical simulation study using CSS after CHOP stage in foamy extraheavy oil reservoirs. However, the conversion timing from CHOP to CSS was not taken into consideration.…”