Study on the Feasibility of Nitrogen Huff-N-Puff in Heavy Oil Reservoirs
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For heavy reservoirs, conventional oil recovery methods are polymer flooding and Steam-assisted Gravity Drainage (SAGD). Such methods are affected by various factors including reservoir thickness, formation heterogeneity, heat loss, and cost, especially in heavy oil reservoirs with depths ranging from 1000 to 2000 m. In these relatively deep reservoirs, the temperature is generally around 40 to 50℃. Their crude oil has a viscosity in the tens of thousands of centipoises at surface conditions, but only a few hundred centipoises at high temperature in the reservoirs. At this reservoir condition, there is sufficient mobility of crude oil making it possible for nitrogen (N2) Huff-n-Puff to be applied. Therefore, this study is to confirm the ability of nitrogen to form foamy oil and the feasibility of nitrogen Huff-n-Puff in relatively deep heavy oil reservoirs. This study includes three types of tests. The first category is the PVT tests to measure N2 solubility in heavy oil. The temperature is set from 50 to 80 ℃ with an incremental increase of 5 ℃, and each temperature has four pressure setting of 3 to 8 MPa. It was found that nitrogen has a lower solubility than carbon dioxide and methane. The solubility of nitrogen in the oil sample at 50℃ and 7 MPa is 7.6 m3/m3. The second category is the pressure depletion tests conducted in a 1-D cylindrical model to observe the foamy oil flow. These tests were conducted consistently at four ii different pressure decline rates. It confirmed the possibility of foamy oil formed by nitrogen and summarized the variation of the flow pattern. The last is the Huff-n-Puff tests conducted in a 2-D planar model to confirm N2 feasibility. It can be concluded that the highest recovery factor of 35.73 % occurs when the pressure decline rate is 16KPa/min. and N2 Huff-n-Puff has a strong potential to recover hydrocarbon in deep heavy oil reservoirs effectively. This research is the first study to apply nitrogen to heavy oil reservoirs. Confirmation of the technology’s feasibility will significantly reduce the cost of exploiting heavy oil reservoir.