Productivity Improvement Using Combination of Static and Dynamic Underbalanced Perforation in Tahe Oilfield, Tarim Basin, West China

摘要

In concern with the skin factor value, the key significant components which do not directly depend on the nature of the reservoir properties are drilling/ completion fluid invasion damage and perforating induced damage. The oil & gas industry has been tried to eliminate the fluid invasion issue by applied deep penetration perforating to bypass the invasion zone and reach un-invaded reservoir. Lots of experiences and lab analysis shows that perforation performance is not meet the expectation of the productivity because of the perforation induced damage. As for now, static underbalanced perforation has been recognized by industry as one of the method to obtain clean perforation tunnel. However, static underbalanced perforation method is not always giving the expected productivity result. Experiments showed that the cleanup of the perforation tunnel was not totally dominated by the static under-balance pressure but also the transient pressure during the first 100 milliseconds of perforation or dynamic under-balance. The dynamic under- balance can be obtained by creating an instantaneous drop in pressure around the guns during perforating. The combination of static and dynamic underbalanced perforation with deep penetration charges which be able to bypass an invasion zone, can create a clean tunnel, and significantly reduce the post-perforating damage by killing fluid, and finally maximized the productivity. This combination of the static and dynamic under balance method has been applied in Tahe Oilfield. Tahe oilfield is located in Tarim basin with reservoir horizon depth of 4100m-4600m，temperature of 94-103 , and pressure gradient is about 1.1MPa/100m. The pay zone is Triassic clastic reservoir with middle porosity and permeability quality. The static underbalanced with different deep penetration charges of perforating system has been applied in Tahe oilfield to improve the productivity. However, the statistic showed that productivity is not reaching the expectation range by static underbalanced perforating. The combination method of static and dynamic under-balance perforation along with deep penetration charges was applied in 2011 to WELL-1. The well productivity was exceeded the expectation and the PI value is almost 2.5 times compare to offset wells which only using static under-balance perforation method. The pressure transient analysis result proved the improvement by showing negative skin value. This paper will describe the application of this technique in Tahe oilfield including: suitable job design, execution of the job and provide the results summary of this successful application. The evaluations of the method are based on productivity improvement and skin value from pressure transient analysis.