低渗透致密气藏水基欠平衡钻井损害评价技术

低渗致密砂岩气藏具有孔喉细小、强亲水、裂缝发育等特点,在作业过程中易于受到损害,即使在欠平衡条件下,仍然具有一定的损害可能.在水基欠平衡钻井条件下,低渗致密砂岩气藏主要的损害方式为水锁和应力敏感.利用裂缝可视化测试系统、毛管流动孔隙结构仪等分析测试手段评价了低渗致密气藏的水锁和应力敏感损害.研究表明,低渗致密气藏在欠平衡条件下仍有很强的水锁损害可能,初始渗透率越低,水锁损害程度越大;有效应力一定时,欠压值越小,水锁损害程度越大,过小的欠压值不能起到保护储集层的作用;欠压值一定时,有效应力越大,水锁损害程度越大.目前对欠平衡条件下的水锁损害评价还处于摸索阶段,下一步工作的重点是储集层原地作业条件的真实模拟以及将室内实验结果应用于现场工程设计.图7表6参13

Damage evaluation for water-based underbalanced drilling in low-permeability and tight sandstone gas reservoirs

With the characteristics such as small pore throats, strong water wetting and well-developed fractures, the low-permeability and tight sandstone gas reservoir is liable to be damaged during operation, even in the underbalanced condition. At water-based underbalanced drilling, water blocking and stress sensitivity are the main damages for low-permeability and tight sandstone gas reservoirs. Such damages are evaluated by using Fractures Visualization Test System and Capillary Flow Porometer. The results indicate that low-permeability and tight gas reservoirs still have very strong water blocking damage in the process of underbalanced drilling, and the lower the initial permeability, the bigger the water blocking damage. Given certain effective stress, the lower underbalanced pressure is accompanied with more serious water blocking damage, and over-low underbalanced pressure can not protect formations. Given certain underbalanced pressure, the higher effective stress brings about more serious water blocking damage. Now, the water blocking damage evaluation in underbalanced condition is just under study. Next work should focus on the simulation of real in-situ operations in reservoir and applying the laboratory evaluation results into onsite engineering design.