A novel experimental method for the evaluation of residual oil distribution in a sand-packed model by using nitrogen and viscosity reducer huff-puff technology to develop heavy oil reservoirs

Abstract

Heavy oil reservoirs are faced with many problems in the development process, such as complex technology, unsatisfactory productivity, and difficult evaluation. Huff and puff as a common method for improving the heavy oil reservoir is popularized. In this work, a brand new evaluation method for residual oil distribution is proposed to evaluate the sweep efficiency of heavy oil under different huff-puff patterns in a sand-packed model. The sand saturated by oil is sequentially taken out from the sand-pack model by using a hand gong drill, and the width of oil stain at every interval of 1 cm along the axis on the oil absorbing paper is measured with a ruler. Based on this innovative laboratory evaluation method, a single pipe model with different oil viscosity and a double pipe model with different permeability levels were designed for three different huff-puff patterns, including nitrogen huff-puff, nitrogen + foam huff-puff and nitrogen + viscosity reducer huff-puff. The results showed that the remaining oil distribution was mainly concentrated in the far well section of 15–60 cm in the sand-packed model. For μo > 10000 mPa s, the overall peak width of the remaining oil by using nitrogen and viscosity reducer huff-puff method was relatively small, which had a better effect on heavy oil development. The experimental results for different permeability differences showed that the peak width at the end of the high permeability pipe was higher (W > 15 cm) because of the terminal crude oil carried by the nitrogen gas in the low permeability pipe constantly coming into the high permeability pipe with low resistance. Compared with the distribution results of the remaining oil in the low permeability pipe with three different huff-puff methods under the same permeability difference, the width peak of the remaining oil generated by using the nitrogen and viscosity reducer huff-puff method was relatively low (w < 13 cm). With the increase of the permeability differences, the peak width difference of the remaining oil at the end of the high/low permeability pipes gradually increased because of the low resistance in the high permeability pipe. Therefore, the remaining oil distribution is intuitively characterized by the application of this new evaluation method and this method reveal the significant reduction of the oil viscosity by using the nitrogen and viscosity reducer huff-puff method to improve the evolution effect of heavy oil.