Study on the Enrichment and Distribution Characteristics of Microscopic Remaining Oil in Heavy Oil Reservoirs After Multiple Huff and Puff

Abstract The composition and properties of heavy oil changed significantly in heavy oil reservoirs after steam flooding or multiple huff and puff. The light components decreased and the heavy components increased by 7% or so after 10 cycles of huff and puff in Zhong'er block of Gudao oil oilfield, resulting in viscosity increase and poorer fluidity. In addition, the steam and the heavy oil formed O/W (oil-in-water) emulsions, which further increased the oil viscosity and hindering fluid flow. The enrichment and distribution characteristics of microscopic remaining oil altered consequently. A three-dimensional large physical sand-filling model was designed to cut out after 10 cycles of huff and puff. Two one-quarter of the model was cut out and each was cut into 27 pieces. The enrichment state of remaining oil in each piece was determined based on its shape and contact relationship with pores and throats. The oil saturation of each piece was recorded and the percentage of different types of remaining oil in each piece was calculated by area statistics method. Experiment results showed that there were 5 enrichment types of remaining oil after multiple huff and puff: continuous, multi-porous, dispersed, single-porous and isolated. With the increase of the enhanced oil recovery, the enrichment type changed from multi-porous to dispersed and then to single-porous. The enrichment types were different in different regions. Close to the huff and puff regions, the remaining oil type was mainly single-porous and dispersed, the proportion of isolated was higher than that in other regions, the continuous was least, and the displacement efficiency was the highest. Far away from the huff and puff regions, the type was mainly dispersed, multi-porous and single-porous. In the corner regions, it was mainly continuous and multi-porous, and the proportion of continuous increased to 25% or so, therefore the displacement efficiency need to be further improved.