Sharp Reductions in High-Productivity Well Due to Formation Damage: Case Study in Tarim Basin, China

Dibei gas condensate field is a fractured tight sandstone reservoir located in the Kuqa depression of YiQiKeLiKe thrust belt, in the northern margin of Tarim Basin, China. We always take reservoir stimulation to improve the well productivity for tight sandstone reservoir. But reservoir stimulation did not reach the expectation value for this area. This paper will provide a case study on stimulation operations of a special well in Dibei gas condensate field. Study well has a high productivity after nitrogen drill. But the production dropped to half after water-based drill. To remove the damage due to drill mud, this well was stimulated three times using acidizing, acidizing fracturing, and hydraulic fracturing. But the productivity was lower and lower after simulation operations. We will describe the process of every operation in detail. The causes of the reductions in productivity will be analyzed comprehensively through experimental tests and comparative analyses. The experiments results show that water blockage and solids invasion of mud are the basic reasons for the sharp reduction in productivity of the well. Acidizing fracturing can remove the damage induced by mud. After a period of workover, solids of mud invaded into natural fractures deeply. In addition,the complex stimulation fluids made the illite particles migration to plug the pore throats. For hydraulic fracturing, water-based hydraulic fluid which made the formation suffers lethal damage. Hydraulic fracturing not only cannot break out the deep damage zone, but also cause more serious damage to reservoir. The production logging test results also show that the formation damage induced by water blockage can reduce the production capacity by more than 40%. Nowadays, reservoir stimulation is still an effective method to improve productivity of well for tight sandstone reservoir. This paper represents a detail introduction of failure case and comprehensively analyzes the causes of these failures from experiments to field. And it also gives a lesson for avoiding this kind of failure and optimizing stimulation design in tight gas condensate to achieve efficiency.