渤海C油田预钻井原油乳化对储层伤害实验研究

Experimental Study on Reservoir Damage Caused by Crude Oil Emulsification of Pre-Drilling Wells in Bohai C Oilfield

渤海C油田导管架期间首批12口预钻井在生产过程出现了生产压差高产量低的现象,分析认为原油乳化堵塞是潜在伤害因素。为了明确原油乳化堵塞机理,为产能恢复措施制定提供指导,针对该批低产井开展原油乳化堵塞实验研究。实验结果表明:当含水率为20%时,原油乳状液黏度为最高值10.9 mPa·s,为原油乳化反相点,乳状液类型为油包水(W/O)型;当含水率大于20%时,乳状液黏度降低,类型为水包油(O/W)型;原油高含水时,乳状液类型为O/W型,降低储层渗透率25.21%,对储层伤害相对较小;原油低含水时,乳状液类型为W/O型,降低储层渗透率75.01%,对储层伤害大。随着乳状液质量浓度从1000 mg·L^(-1)增加至4000 mg·L^(-1),岩心渗透率伤害程度最高达到50%。以I01H和I28H井为例,结合实验结果对实际生产动态进行分析,两口井生产初期含水率升高至20%后,生产压差不变,采液指数下降,说明原油发生乳化并堵塞近井地层,与实验结果一致。

In the process of production,the first batch of 12 pre-drilling wells generated the condition of well high production pressure difference and low production rates in Bohai C oilfield.According to preliminary analysis,the crude oil emulsification plugging is considered as a potential reservoir damage factor.In order to clarify the mechanism of crude oil emulsification plugging and provide guidance for production recovery measures,the experimental study on crude oil emulsification plugging was carried out based on the batch of low-production wells.The experimental results showed that,when the water cut was 20%,the viscosity of crude oil emulsion reached to the highest value of 10.9 mPa·s,which came to be the emulsification inversion point of crude oil,and the type of emulsion developed into water-in-oil(W/O)type.When the water cut was greater than 20%,the viscosity of the crude oil emulsion decreased,and the emulsion type developed into oil-in-water(O/W)type.When the crude oil reservoir had high water cut,the emulsion type converted to O/W type,which reduced the reservoir permeability by 25.21%,and it made relatively small damage to the reservoir.When the crude oil reservoir had low water cut,the emulsion type developed into W/O type,which lessened the permeability of the reservoir by 75.01%,and it made significant harmful to the reservoir.When the mass concentration of the emulsion increased from 1000 mg·L^(-1)to 4000 mg·L^(-1),the core permeability damage was up to 50%.Taking wells I01H and I28H as examples and by analyzing their production trends based on experimental results,the production pressure differences remained unchanged and the fluid production index decreased after the water cut of the two wells increased to 20%in the initial stage of production.These indicated the emulsified crude oil blocked the formation near the hole,which was consistent with the experimental results.