Yi-Bo Li

High temperature and oil tolerance of surfactant foam/polymer–surfactant foam

Foam performance during oil displacement is closely related to the reservoir environment. In this study, both bulk and porous media experiments were conducted to investigate surfactant foam and polymer–surfactant foam behaviors at high temperature and with crude oil. After aging at 90 °C for 90 days, the foam drainage half-life of the aged polymer–surfactant foam was four times longer than that of the fresh surfactant foam. Scanning electron microscope images indicated that, even experienced high temperature aging, the polymer and surfactant could still develop multilayer complexes to enhance the foam film strength. Within a certain oil content, the foam stability in the presence of oil could be better than in the absence of oil. Stereoscopic microscope images revealed that the existing form and content of oil in the foam film had played a vital role. Core flooding experiments further confirmed that stable surfactant foam and polymer–surfactant foam could generate in the presence of waterflooded residual oil and give rise to additional oil recovery of 15.35% and 35.75% at 90 °C, respectively. The positive responses of this study may be attractive to potential foam field applications.

Low-temperature isothermal oxidation of crude oil

ABSTRACT In this work, the low-temperature oxidation (LTO) characteristics of different API gravity crude oils, involving one light, one medium, and one heavy, are studied comprehensively from the aspects of effluent gas, oxidized oil, and pressure drop. The results reveal that heavy oil exhibits faster LTO reaction rate and stronger O2 consumption capability compared with lighter ones. There are a certain amount of carbonaceous deposits in oxidized oils and the carbonation progress of heavy oil is brought to a deeper degree. The pressure drop rule of oil samples is speculated to be the consequence of “skin effect” and crude oil with more heavy species shows higher oxidation activity, which contributes to an improved understanding about the LTO mechanism from the molecular perspective and needs further research.

Utilisation of multiple gas injection to enhance oil recovery for fractured-cavity carbonate heavy oil reservoir

Gas injection has been proven to be a valuable enhanced oil recovery (EOR) process for light oil reservoirs and ordinary heavy oil reservoirs, but it was rarely proposed as an EOR process for fractured-cavity carbonate heavy oil reservoir. This study aims to investigate the feasibility of the gas injection based on flooding and cycle stimulation method with respect to enhancing oil recovery for fractured-cavity carbonate heavy oil reservoir. Thus, a representative physical model of core was designed, and some gas flooding and cyclic gas stimulation experiments were conducted. The experimental results show that gas injection can enhance the oil recovery in fractured-cavity carbonate reservoir and carbon dioxide is the optimal injected gas in this study. Also, gravity drainage plays an important role in fractured-cavity carbonate reservoir besides the various recovering mechanisms in conventional reservoir. In addition, Tahe heavy oil has a strong capacity of oxygen consumption due to the high content of polar compound. [Received: May, 1, 2015; Accepted: February 29, 2016]

Identification of Highly to Over Mature Gas Interval Using Reservoir Bitumen Features: Sichuan Basin of Southwest China

The identification of oil and gas intervals has been mainly constrained by the interpretation on well logging data. However, this has met great difficulties with petroleum accumulation cases becoming more and more complex. The authors discuss an identification of highly to over mature gas interval using bitumen features, based on a case study in the Sichuan Basin of southwest China. The bitumen in the gas interval is characterized by relatively rich low-weight n-alkanes with a single pre-peak. In addition, pregnane, homopregnane, and tricyclic terpanes are enriched. Thus, the indicated maturity is highly to over mature. The late-arrived highly mature oils were cracked into gas, with little filling of bitumen in reservoir space. By contrast, the bitumen in the interval with little bearing of gas has opposite features. It is relatively enriched in high-weight n-alkanes and extremely low abundance of pregnane, homopregnane, and tricyclic terpanes. Thus the oils in such dry intervals are mostly low-mature early arrived oils, which tightly adsorbed on the carbonate grains. The pore space is almost fully filled by bitumen, being unfavorable for gas charge and preservation. As these features are all collected from routine analyses, the method can be applicable. The results can provide new fundamental information for regional oil testing and petroleum exploration, thereby reducing economic loss and exploration risk. In addition, the results also have wide implications for the other works with similar aims.

Variation of reservoir fluid property during the high pressure air injection process

ABSTRACT This research aimed at determining the variation of reservoir fluid property during the high-pressure air injection process. For this purpose, the forward multiple contact experiment was employed by pressure–volume–temperature (PVT) system to investigate the physical property variation of the crude oil and the complex oxidation reactions. The results show: under the relative low temperature and pressure condition, instead of carbon dioxide, carbon monoxide dominates the products in the air phase. The gas/oil ratio and volume ratio increased due to the generated gas while the viscosity and density achieved a descending trend. The colloid and bitumen in the oil phase reduced by half but the amount of wax achieved a small increase. The low-temperature oxidation and pyrolysis reactions caused the fluctuated change of the different compounds. The amount of light compounds decreased at the beginning and then increased while that of heavy compounds showed the opposite trend. But at last, due to the H/C ratio, the light compounds increased to more than their initial value.