An Innovative EOR Method for Waterflooding Heterogeneous Oilfield ---- Graded Diversion-Flooding Technology and Verification by Field Comparison Tests

Abstract XJ6 is a conglomerate reservoir, with oil viscosity 80mPa.s. The reservoir is quite heterogeneous, and seriously uneven sweeping exists. For exploring high efficiency EOR method, three types of EOR models were designed, utilizing continuous phase crosslinked polymer gel (LPG), nano-micro grade particle type polymer SMG dispersion, and millimeter grade pregelled swellable particle (SLG). And field comparison tests were conducted. In field tests, the chemical slug injection started in April 2013 and ended in January 2015. The injection liquid amount was 0.2PV. Model 1 features preset plugging slug of LPG carried SLG and the following oil displacing slug of LPG slugs with different viscosity, and the pilot consists of 25 injectors and 42 producers. Model 2 features preset plugging slug of LPG carried SLG and the following 4 times of alternate injection of SMG slug and small LPG slug, and SMG dispersion is the main slug in the model. Model 3 features three times of alternate injection of water and high viscosity LPG combined with SLG slug. Model 1 and Model 2 obtained obvious effect quickly. For Model 1, due to continuous injection of viscous fluid, both of oil flowing resistance and water flowing resistance greatly increased, leading to low liquid supplying capacity for the producers, so the effect of oil increasing and water cut decreasing could not be further improved or sustained for a long period. For Model 2, the small slugs of SLG and LPG pluged or inhibited the macroscopic and midscopic scales of prevailing flowing, and the main slug of low apparent viscosity SMG dispersion was used to deal with the microscopic scale uneven sweep, in which, with the SMG particles temperarilly inhibiting the big pores or high permeability area, the water was diverted into small pores or low permeability area to efficiently displace the relatively high saturated remaining oil there. So Model 2 obtained better effect of oil increasing and water cut decreasing. During chemical injection in Model 2, the daily oil rate increased by 2.9 times, and that of Model 1 is 1.1 times. And the maximum water cut decrease of Model 1 and Model 2 was 32.2 and 46.2 percent respectively. Model 3 did not show obvious EOR effect. The field comparison tests verified the advancement of Model 2, which features multi-grade diversion and displacement, and the scientific nature of syncronouse diversion and displacement mechanism. It also obtained economical success. Therefore, for waterflooded reservoir with complex pore structure and high heterogeneity, the multi-grade divertion and displacement technology can be used to greatly improve utilizing efficiency of the injected water, achiving the aim of oil recovery enhancement.