Research and Practice on Gas Channeling Controlling by Combined Stimulation for Multi-Thermal Fluids Huff and Puff

Cycle steam stimulation has been widely used in land oil field. In order to get higher oil recovery rate and higher cumulative oil production, one improvement work of cyclic steam stimulation is injection N2 and CO2 together with steam to enlarge the heated radius, and the pilot test of multi-thermal fluids huff and puff were carried out in offshore heavy oil in Bohai. There were 10 horizontal wells which have accomplished the 1st cycle stimulation, and 6 wells have accomplished the 2nd cycle stimulation. There were 4 well times of gas channeling in the 1st cycle injection, and 9 well times in the 2nd cycle injection. Because of the formation pressure drop, gas channeling became more serious with the increase of stimulation cycles. Based on the well performance, the reason and characteristic of gas channeling for injection multi-thermal fluids were analyzed, which is different from that of steam injection. Based on a numerical model, a quantitative researched about the influence of gas channel to thermal well was carried out. In order to manage the gas channeling, a combined stimulation program was purposed. Case study of gas channeling controlling by combined stimulation in N heavy oil field in Bohai shows that, the combined stimulation can relieve the risk of gas channeling. The new multi-thermal fluids injection model is of great significance for thermal recovery of offshore heavy oil

Techniques for improving the water-flooding of oil fields during the high water-cut stage

International audienceThe multi-layer co-exploitation method is often used in offshore oilfields because of the large spacing between the injection and production wells. As oilfields gradually enter the high water-cut stage, the contradiction between the horizontal and vertical directions becomes more prominent, and the distribution of the remaining oil is more complex. Oilfields are facing unprecedented challenges in further enhancing oil recovery. Using oilfield A, which is in the high water-cut stage, as the research object, we compiled a detailed description of the remaining oil during the high water-cut stage using the information collected during the comprehensive adjustment and infilling of the oilfield. In addition various techniques for tapping the potential reservoir, stabilizing the oil, and controlling the water were investigated. A set of key techniques for the continuous improvement of the efficiency of water injection after comprehensive adjustment of high water-cut fields was generated. Based on the determined configuration of the offshore deltaic reservoir, a set of detailed descriptive methods and tapping technology for extracting the remaining oil in the offshore high water-cut oilfield after comprehensive adjustment was established. By considering the equilibrium displacement and using a new quantitative characterization method that includes displacement, a new technique for determining the quantity of water that needs to be injected into a stratified injection well during the high water-cut stage was established. Based on the principle of flow field intensity reconfiguration, a linear, variable-intensity, alternating injection and withdrawal technique was proposed. With the application of this series of techniques, the increase in the water content was controlled to within 1%, the natural reduction rate was controlled to within 9%, and the production increased by 1.060 × 107 m3

The Displacement Behaviors of Different Pore-Scales during CO₂ Flooding and Huff-n-Puff Processes in Tight Oil Reservoirs Using Nuclear Magnetic Resonance (NMR)

Injecting CO2 into tight oil reservoirs is a potential approach for enhanced oil recovery (EOR) and CO2 sequestration. However, the effects of different pore-scales on EOR are poorly understood, and this has a significant impact on recovery. In this paper, a pore size correction model based on X-ray computerized tomography (CT) and nuclear magnetic resonance (NMR) was developed in order to establish the relationship between the pore radius and the transverse relaxation time. Different pore-scales are divided according to the cumulative distribution characteristics of the transverse relaxation time (T2). CO2 flooding and huff-n-puff experiments were conducted to investigate the dynamic displacement behaviors in different pore-scales. The results indicate that there are three pore-scales: micropores (T2 T2 T2). However, there are also pseudo-sweep pores (PPs), equilibrium pores (EPs), and sweep pores (SPs) in the intermediate pores, depending on whether crude oil has been produced. Interestingly, the pressurization process causes some crude oil in the large pores to be squeezed into small pores. The recovery of CO2 huff-n-puff (19.75%) is obviously lower than that of CO2 flooding (51.61%). Specifically, it was observed that the micropores (−8%) and the pseudo-sweep pores (−37%) have a negative impact on oil recovery, whereas all pore-scales exhibit positive effects during CO2 flooding. In addition, it was found that the critical pore radiuses of CO2 flooding and huff-n-puff were 2.61 ms (0.15 µm) and 25 ms (1.5 µm), respectively, in the experiments, and that there is also more oil remaining in the macropores and the sweep pores during CO2 huff-n-puff. These results provide a deeper understanding of the displacement behaviors of different pore-scales in tight oil reservoirs