| Shizigou N1reservoir temperature is50℃. And the average salinity of formation water is23×104mg/L. Thus, the reservoir is a high salinity reservoir. The average porosity of the reservoir is15.12%. And the average permeability is33.1×10-3μm2. It has medium porosity and permeability characteristics. This reservoir has feature of low porosity and low permeability. The reservoir has strong heterogeneity, lead to serious water channeling during waterflooding process and lower waterflood sweep efficiency. Besides, due to the high salinity, general agent for flooding control is difficult to play a significant role, further increasing the difficulty of controlling water stability of the oil. Based on investigation of experiments and applications on high salinity reservoir deep flooding, proposing for the control of water-stable oil reservoir technology-"Salt weak gel/pore-scale Microspheres" composite deep flooding technology. Weak Gel is an ideal deep flooding agent. It can produce plugging in hypertonic channel, making follow-up steering fluid. It will transport towards deep formation to reach the effect of flooding.For general weak gel is difficult to adapt to high salinity reservoir conditions, this paper developed target weak gel system which is adapt to high salinity environment reservoir through the appropriate choice of the preferred drug and concentration. Pore scale microspheres has excellent salt resistance, blocking its passage in a weak gel hypertonic basis, playing a role in the small pores. Through the accumulation and swelling effect, microspheres produced pore throat plugging and elastic deformation under pressure through the pore throat, continue to produce at the next block, in order to achieve deep flooding and steering fluid deep role.Through experiments, a weak gel system has been developed, which is suitable for Shizigou N1reservoir under the high salinity environment. The formula is:1700mg/L KYPAM-6+150-200mg/L complex cross linking agent+100mg/L oxygen scavenger. The cross linking agent consists of organic chromium and phenolic aldehyde in a ratio of1:1. Phenolic aldehyde is composed of pharmacy formaldehyde and resorcinol in a certain proportion. The weak gel system has good properties of salt resistance, temperature resistance, shearing resistance and long-term stability, which is well-adjusted to the reservoir. Core flow experiment results show that the enhanced recovery is10.2%and the improvement rate of injection profile is82.3%, and the particle size of the SD-320microspheres is a good match for the pore throat size of the reservoir rock. The SD-320microspheres have good properties of water swelling, salt resistance, temperature resistance and long-term stability, which expansion rate is5.08in fresh water and1.03in formation water after swelling for30days under the reservoir temperature of50℃, and they still have a good stability after swelling for60days in formation water. Core flow experimental evaluation results show that the ability of oil displacement and profile control of the microspheres in the low permeability formation are clearly more effective than that of in the high permeability formation.Experimental evaluation of compatibility studies show that the performance of both will be affected each other to some extent when the two systems mixing before gelation of weak gel. After gelation, the performance of both will not be affected, having good compatibility. On this basis, the injection sequence selected as "weak gel is injected first, and then injected the microspheres" by comparative experiment. Besides, weak gel injected slug size is0.3PV, and microspheres injected slug size is0.3PV. However, the slug concentration of microspheres is3000mg/L. Experimental results show that the effect of multi-round flooding is better than that of single-round injection of the composite system. This paper also study flooding mechanism of composite system. Results of this study have important significance for improve waterflood development on Shizigou N1reservoir. |
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