Experimental study on foamy oil flow behavior of a heavy oil-N2 system under reservoir condition

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 deep heavy oil reservoirs. In these deep reservoirs, 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. There is sufficient mobility of crude oil making it possible for nitrogen (N2) huff-n-puff to be applied. Since foamy oil is a very significant production mechanism in huff-n-puff process, this study is to confirm the ability of nitrogen to form foamy oil in a deep heavy oil reservoir. This study includes two types of tests. The first category is the PVT tests to measure N2 solubility in heavy oil. It was found that the solubility of nitrogen in the oil sample at 50 °C and 7 MPa is 7.54 m3/m3. The second category is the pressure depletion tests conducted in a 1-D cylindrical model to observe the flow behavior. These tests are conducted consistently at four different pressure decline rates. It confirmed the possibility of foamy oil formed by nitrogen and summarized the variation of the flow pattern. This research is a preliminary basic study of N2 huff-n-puff in heavy oil reservoirs. Confirmation of the technology’s feasibility will significantly reduce the cost of exploiting heavy oil reservoir.