Production Enhancement in Deep Sour Gas Field: A Case Study in China

Abstract

Puguang is the biggest sour gas field in China with 17% H2S and 9% CO2 concentration and is the major gas sources for the pipeline from Sichuan to Shanghai. It's important to keep the gas wells healthily and steadily producing. However, the production is continually declining due to water coning, scale buildup and formation pressure dropping. It's urgent to perform well intervention effectively and economically to increase the well production. Production logging in multiple wells identified that inflow zones were less than 30% of perforation interval because of formation invasion and perforation tunnel plugging from initial completion. To release the potential productivity from nonproducing zones, reopening the perforations is critical to reverse the trend of production decline. To pass through the 3.5-in tubing with minimal restriction of 2.7-in and to effectively perforate the 7-in production casing and the carbonate formation, a 2.5-in spiral-exposed perforation system was finally selected as the optimized solution that can achieve the deepest formation penetration compared with conventional carrier system from simulations with rock-based perforation model. The spiral-exposed perforation system was modified to be H2S resistant, and wellbore dynamic simulation was conducted to minimize the gun shock to avoid gun drop during detonation. The detailed job design and risk mitigation plan were made as well to avoid any failure in such a highly corrosive environment with well depth up to 6,000 m. The first reperforation job was conducted successfully, and the well production increased 130,000 m3/day or 22.8%, and afterward, production logging confirmed that zonal production had significantly improved from the newly perforated interval. Then another seven wells were reperforated with an interval of 30 m to 45 m and average 100,000 m3/day gas production increment or 20% per well was achieved. It's proven that reperforation with redesigned exposed perforation system is the effective and economical way to increase production in the Puguang gas field. This paper illustrates how and what we do for exposed system improvement, candidate well selection, planning, and executing the through-tubing exposed perforation in such extremely challenging conditions. It also discusses lessons learnt and recommendations for future well intervention to steadily increase the well production in the Puguang gas field.