Experimental Study of Synergy between Polymeric Microspheres and Nanoemulsions for Profile Control and Water Plugging

Abstract

The development of low-porosity and low-permeability oil reservoirs in the Changqing oilfield presents a significant challenge due to the high injection pressure and limited space for profile control and pressure raising. Therefore, the synergistic profile control and flooding technology of polymer microspheres (PMs) and nanoemulsions is proposed, which makes use of the plugging performance of PMs and the pressure-reducing and oil-driving properties of nanoemulsions, with the objective of controlling the water-absorbing profile and increasing the recovery rate. The paper assessed the properties of nanoemulsions and PMs and evaluated their suitability for reservoirs. The construction parameters of profile control and flooding were optimized on an experimental basis. The experimental results demonstrate that the initial particle size of microspheres can more closely match the pore diameter of the formation and that the core exhibits a higher plugging rate after hydration and expansion. Moreover, the nanoemulsion can effectively reduce the interfacial tension, thereby exerting a beneficial effect on pressure reduction. The construction parameters of microspheres and nanoemulsions were optimized by alternately injecting them with 2:1 multistage plugs, and the injected pressure was lowered by 43%, with a high plugging rate and value-added recovery rate of up to 26.5%. Based on the experimental study, 8 well sets of field tests were conducted, and the results demonstrated that the efficiency rate of profile control reached 50%. Furthermore, the average injection pressure of the injected wells decreased by 1.7 MPa, the rise in water content decreased by 2.27%, and the petroleum production increased by 1110.2 tons. The validity period reached 162 days, indicating a positive application effect.

Figure 1

Pore size distribution of the sample core.

Figure 2

Flowchart of the single-phase core displacement experiment.

Figure 3

Double-tube core displacement experiment flowchart.

Figure 4

(a) Initial particle size after emulsification of microspheres (b) aging particle size expansion pattern of microspheres.

Figure 5

Pressure profiles of microsphere injection at different concentrations. (a) Injection concentration: 1000 mg·L^–1. (b) Injection concentration: 2000 mg·L^–1.

Figure 6

Plugging rate evaluation histogram. (a) Plugging rate. (b) Resistance coefficient vs residual resistance coefficient.

Figure 7

Particle size distribution curve of micro- and nanoaugmentation agents.

Figure 8

Oil–water interfacial tension of the nanoemulsion.

Figure 9

Single-injection oil drive profile: (a) 0.3 PV microspheres and (b) 0.3 PV nanoemulsion.

Figure 10

Mixed- and alternating-segment plug injection. (a) 0.3 PV mixed injection, (b) 0.1 PV microspheres +0.2 PV emulsion alternating, (c) 0.15 PV microspheres +0.15 PV emulsion alternating, (d) 0.2 PV microspheres +0.1 PV emulsion alternating, and (e) 0.15 PV microspheres +0.15 PV emulsion +0.15 PV microspheres +0.15 PV emulsion. (f) Effect of different segment plug injections on the rate of pressure reduction.