低渗致密砂岩凝析气藏液锁损害机理及防治——以吐哈油田丘东气藏为例

Mechanism and preventive techniques of fluid-block damage for tight sandstone condensate gas reservoirs with low-permeability:Taking Qiudong gas reservoir of Tuha Oilfield as an example

吐哈油田丘东低渗凝析气藏钻采过程中存在不同形式的液锁损害,系统分析了其损害机理和主要影响因素。液锁损害程度主要与岩心的渗透率、孔隙度、初始含水饱和度及油水界面张力有关,还与储集层岩性、胶结物类型及含量、孔隙结构特征和侵入流体的性质有关。针对钻/完井、生产、储集层改造及修井过程中液锁损害机理及特征,研发出防液锁低损害成膜钻井液及保压、增能、助排等综合防治技术,改进的钻井液可使受损害储集层岩心的渗透率恢复值由平均54%提高到81%,研发的助排剂可明显提高残酸的返排效果(助排率达88.9%),改进的修井液可使岩心渗透率恢复值提高16.1%,各种改进工艺在现场应用后,较好地保护了产层,提高了低渗透气藏的综合开发效益。

Various forms of fluid-blocking are easily induced during the processes of drilling/completion and production in the Qiudong gas condensate reservoir. The main factors that cause fluid blocking include core permeability, porosity, original water saturation, and oil-water interracial tension, as well as lithologic characteristics, types and content of cementing substances, pore structure, and properties of invasion fluids. Based on the damage mechanisms and characteristics of fluid-blocking during the drilling/completion, production, fracturing, acidizing and workover operations, a set of matching techniques were developed to minimize fluid-block damage, which mainly include fluid-block prevention, low damage, film-forming drilling fluid, as well as the techniques for keeping proper formation pressure, enhancing formation pressure and improving drainage rate. The modified drilling fluid system can improve the return permeability of test cores from averaged 54% to 81%. The newly developed cleaning up agent consisted of combinational surfactants can improve the drainage rate of backflow acid （up to 88. 9%）, the newly developed solids-free work-over fluid system can improve the return permeability by 16.1%. After the application of the new techniques, the pay zone is preserved better, with the comprehensive development investment benefits enhanced.