Abstract
During the later period of steam injection, the oil production largely decreases to be a state of low production or low oil–steam ratio. In this article, a classification method of low production wells was established and some measures of improving oil production were researched for the low production wells during thermal recovery. Three visualization experiments were implemented to analyze the sweep efficiency and to measure the oil recovery factor during injecting different flooding agents. Then a novel diagram was introduced to guide us how to precisely choose the appropriate measures for the low production wells during thermal recovery in heavy oil reservoirs. According to the statistical results, the low production wells can be categorized into three types involving high degree of oil recovery, thermal disturbance (even steam channeling) among wells and dual factors. The results of visualization experiments showed that the injection of chemical agents can effectively increase the displacement efficiency in swept zone after steam injection. Temperature-resistant gel or foams can be used to decrease thermal disturbance and even steam channeling among wells during steam injection in heavy oil reservoir. The values of a new parameter can be employed to confirm the boundary of different improvement measures. Finally, a diagram was established to help choosing appropriate measures involving nitrogen injection, foam injection, gel injection and invalid measure.
Highlights
The reserves of heavy oil around the world are about 9000 × 108 m3, which is equivalent to 2.5 times of the reserves of light oil
The results show that the viscosity reducer significantly increases the displacement efficiency, but the sweep efficiency hardly largely increases only through adding nitrogen or viscosity reducer after steam channeling (Green et al 1991; Kam et al 2007; Siddiqui et al 2003)
By introducing new parameters, [KHe∕( Ln o)] Vk, we divided low production wells of thermal recovery into three types involving the higher degree of oil recovery, the steam channeling among wells and the dual factors
Summary
The reserves of heavy oil around the world are about 9000 × 108 m3, which is equivalent to 2.5 times of the reserves of light oil. Heavy oil can be considered an alternative energy source of light oil on earth (Yang and Han 1991; Thomas 2007). Thermal recovery is an important technology for developing heavy oil reservoirs (Jabbour et al 1996; Fatemi and Jamaloei 2011). Steam stimulation is a key tool to achieve economic production of heavy oil. The primary object of the steam injection is to increase temperature and decrease oil viscosity near the wellbore. The initial oil rate is high because of enough oil saturation, large reservoir pressure and low oil viscosity. While, during the production stage, as oil saturation becomes lower, reservoir
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