Preparation and Application of a Block Removing Fluid for Eliminating Reservoir Contamination by High Density Oil-Based Drilling Fluids
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摘要: 油基高密度钻井液因其高度的稳定性和抑制性，在钻井过程中有着广泛的应用，但因其经过滤失、迁移后所形成的重晶石滤饼对储层有着很大的危害，导致油气产量下降。常规化学方法如酸溶，碱溶等方式难以解除滤饼造成的污染。以螯合剂DTPA为主体，添加碳酸钾为转化剂、草酸为催化剂、过硫酸铵为氧化剂，结合以AEC为表面活性剂和乙二醇丁醚为有机溶剂，形成了一套稳定、高效的油基高密度解堵液体系，其对钻井液滤饼渗透、螯合、增溶及洗涤作用，能破坏油基钻井液滤饼内部结构，降低物质间的胶黏作用，增加对油基高密度钻井液污染的解除。高密度钻井液固相螯合液配方为：20%DTPA+3%草酸+6%K2CO3+0.06%过硫酸铵+KOH，油相清洗液的最终配方为：12%乙二醇丁醚+0.5%AEC，对该体系解堵能力，油相清洗能力进行评价。结果表明，在不同的温度条件下（120℃～180℃），复合解堵体系均能对高密度钻井液滤饼有效降解，120℃下单级处理4 h达到66.7%的滤饼溶解率，在120℃多级处理4 h对滤饼的溶解率为72.22%，且滤饼溶解率随温度上升也同时增加，180 ℃多级处理8 h后溶解率为89.24%，最高腐蚀速率为1.1537 g/(m2·h)，其具有优秀的解堵性能和耐温性能，在同等实验条件下，复合解堵方法较常规螯合解堵方法对油基钻井液滤饼的溶解效率提升了20%左右，经现场试验证明，该体系能有效解决高密度钻井液所造成的污染及堵塞，其产能恢复率为90%左右。Abstract: High density oil-based drilling fluids have been widely used in the well drilling operation due to their high stability and inhibitive capacity. However, barite filter cakes formed after filtration and migration of the high density oil-based drilling fluids cause great harm to the reservoir, resulting in reduced oil and gas production. The contamination caused by the barite filter cakes is difficult to remove by conventional methods such as acid dissolution and alkali dissolution. In this study, a stable and efficient block removing fluid was formulated with the chelating agent DTPA as the main component, potassium carbonate as the conversion agent, oxalic acid as the catalyst, ammonium persulfate as the oxidant, AEC as the surfactant and ethylene glycol butyl ether as the organic solvent. This block removing fluid, through penetration, chelation, solubilization and washing on the mud cakes, destroys the internal structure of the mud cakes formed by oil-based drilling fluids, reduces the inter-substance adhesive force, and enhances the removal of the contamination by high density oil-based drilling fluids. The composition of the solid-phase chelating liquid for high-density drilling fluids is:20%DTPA+3%oxalic acid+6%K2CO3+0.06%ammonium persulfate+KOH, and the final composition of the oil-phase cleaning liquid is: 12% ethylene glycol butyl ether+0.5%AEC. Evaluation of the performance and oil cleaning ability of this block removing fluid shows that under different temperatures (120℃-180℃), the composite block removing fluid can effectively degrade the filter cakes produced by high-density drilling fluids. Single-stage treatment at 120℃ for 4 hours can reach a filter cake dissolution rate of 66.7%, and multi-stage treatment at 120℃ for 4 hours has a filter cake dissolution rate of 72.22%. Moreover, the filter cake dissolution rate increases with temperature. After the multi-stage treatment at 180℃ for 8 hours, the dissolution rate is 89.24%, and the highest corrosion rate is 1.1537 g/(m2·h). It has excellent block removal performance and temperature resistance. In the same experimental conditions, the dissolution efficiency of the composite block removing method for the mud cakes produced by oil-based drilling fluid is about 20% higher than that of the conventional chelating block removing method. Field tests have proved that this system can effectively solve the contamination and block by high-density drilling fluids, and the production capacity recovery rate can be as high as about 90%.
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表 1 添加不同氧化剂的滤饼溶解实验结果
氧化剂类型 反应前滤饼+
滤纸质量/g反应后滤饼+
滤纸质量/g溶蚀率/
%未添加氧化剂 2.1069 1.6386 47.56% 0.02%过硫酸铵 2.0757 1.5792 52.42% 0.02%过硫酸钾 2.1842 1.6381 50.12% 
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表 2 表面活性剂对接触角的改变程度
表面
活性剂处理前
接触角/(°)处理后
接触角/(°)接触角
改变率/%AES 105.26 84.77 19.47 CDEA 98.05 64.19 34.53 AEC 121.02 69.81 42.32
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表 3 不同解堵液常压静态腐蚀实验结果
液体
类型钢片
编号钢片初
质量/g钢片腐蚀后
质量/g腐蚀速率/
(g/(m2·h))螯合解堵液 739 11.4235 11.4171 1.1537 清洗液 181 10.9524 10.9521 0.0538 螯合液+清洗液 340 11.3045 11.3007 0.6882
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