Study and Application of a New Self-diverting Acid for Use in Sandstone Fracturing
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摘要: 渤海主力油田储层层间渗透率级差大、非均质性强，酸化过程中酸液大量进入高渗层，引起渗透率级差进一步加剧，不能有效改善中低渗层，酸化解堵效果不理想。针对该问题，以新型两性离子表面活性剂ZX-1为稠化剂，优化形成了砂岩自转向酸体系，对该体系开展了流变性、配伍性、破胶性能、转向酸化效果评价实验。结果表明模拟鲜酸黏度6mPa·s，利于注入储层；模拟自转向酸变黏体系黏度60 mPa·s，耐剪切性强；模拟残酸黏度2 mPa·s，利于返排。自转向酸与缓蚀剂、铁离子稳定剂、防膨剂及助排剂配伍性良好，无沉淀、残渣产生；体系破胶容易，异丙醇、破乳剂、乙二醇丁醚及酸液消耗均能使自转向酸完全破胶，破胶后溶液黏度均低于10 mPa·s；体系具有自我清洁的作用，即使现场酸液未能完全破胶，经过一段时间能自动破胶，不会对储层造成永久性伤害。该自转向酸体系具有良好转向分流能力，随着初始渗透率级差从比2.00增大到10.70，酸化后低渗岩心渗透率改善倍数明显增大，高低渗岩心渗透率级差比减小，当渗透率级差达到10.7时，体系仍能实现有效分流酸化。ZX-1自转向酸现场应用效果明显，具有良好应用前景。Abstract: The main reservoirs in the Bohai oilfield are characteristic of big permeability differences between different production layers, and high heterogeneity. This has resulted in the acid solution flowing mainly into the high permeability layers, further aggravating the permeability differences, making it difficult to effectively improve the conductivity of the layers with medium and low permeability, and resulting in poor acidizing job quality. A new self-diverting acid was developed to deal with these problems. The self-diverting acid was viscosified with ZX-1, an amphoteric surfactant. Laboratory experiments have been conducted on the rheology, compatibility, gel-breaking and the diverting acid stimulation performance of the self-diverting acid. It was shown that the simulated fresh acid had viscosity of 6 mPa·s, which was easy to inject into reservoir formations. The viscosified simulated self-diverting acid had viscosity of 60 mPa·s, highly resistant to shearing. And the simulated residue acid had viscosity of only 2 mPa·s, easy to be flowed back. The self-diverting acid was well compatible with corrosion inhibitors, iron ion stabilizers, swelling inhibitors and cleanup additives, and no precipitation and residue were observed in the experiments. Gel breaking of the self-diverting acid was easy to realize with isopropyl alcohol, demulsifiers, ethylene glycol mono-butyl ether and acid solutions. Viscosity of the self-diverting acid after gel breaking was less than 10 mPa·s. Part of the gel within the viscosified acid may not be broken at the time of application, but with time, it will automatically become broken, rendering no permanent damage to the potential of reservoir. The self-diverting acid had good diverting property, with the permeability difference ratio increased from the initial value of 2.00 to the final value of 10.70. After acid stimulation, the permeability of the low-permeability layers was enhanced remarkably, and the permeability differences between the high-and low-permeability layers were reduced. When the permeability difference reached 10.7, diverting acid stimulation can still be achieved. Based on the results of the field application, the self-diverting acid will find wide application in the future.
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Key words:
- Self-diverting acid /
- Sandstone /
- Acid stimulation /
- Oilfield stimulation /
- Amphoteric surfactant /
- Bohai oilfield
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