Abstract
Jilake Reservoir TII in Tarim Basin, China, is characterized in high clay content, great water sensitivity, small difference between formation pressure and dew point pressure, severe retrograde condensation pollution, water output of gas reservoir and serious water blocking at the low-permeability position of the reservoir, imposing restrictions on the productivity of oil & gas wells. Sensitivity experiments showed that Jilake Reservoir TII was strongly sensitive to water, weakly sensitive to alkali and weakly sensitive to stress. Dynamic core displacement results showed that conventional water-based drilling fluid causes 40% permeability damage. SEM imaging indicated illite/smectite on the rock surface swelled and blocked the primary pore after encountering the drilling fluid. Besides, conventional water-based fracturing fluid caused 70%-90% damage to the permeability, and the SEM results also showed clay minerals swelling after absorbing water from the fracturing fluid. Experiments also showed that that the damage of retrograde condensation was also serious and 15% condensate oil reduced the gas permeability by 30%-60%. Moreover, water blocking damage also occurred to Jilake Reservoir TII, and the damage extent of gas permeability was a function of water saturation. However, the damage can be remitted by adding clay stabilizer and reverse wetting agent into the operating fluid. The laboratory tests indicated that the anti-swelling rate of the clay stabilizer reached 143.8%; the addition of the reverse wetting agent resulted in permeability increase by 3 times for formation water and 1.76 times for condensate oil.
Highlights
Located on the southeast wing of the large buried anticline from the middle section of Tabei Uplift to Lunnan, Jilake Structure is at the transitional zone of the uplift and two depressions, adjacent to Manjia’er Depression in the south, and leaning against Caohu Secondary Depression in the east
The Reservoir is featured by strong heterogeneity, high content of clay mineral, complex oil, gas & water system and gas reservoir type and small difference between formation pressure and dew point pressure
There are very few reservoirs like Tarim Jilake Reservoir TII, which has a potential of comprehensive damage of water sensitivity, retrograde condensation and water blocking, and no single technology can solve the problem
Summary
Located on the southeast wing of the large buried anticline from the middle section of Tabei Uplift to Lunnan, Jilake Structure is at the transitional zone of the uplift and two depressions, adjacent to Manjia’er Depression in the south, and leaning against Caohu Secondary Depression in the east. Jilake Condensate Gas Reservoir TII on this structure is a sandstone reservoir with high porosity and high permeability. The Reservoir is featured by strong heterogeneity, high content of clay mineral, complex oil, gas & water system and gas reservoir type and small difference between formation pressure and dew point pressure. Jiangyu Liu et al studied the water blocking damage of the tight sandstone in Tarim Basin, China, and proposed a solution of nano fracturing fluid [5]. There are very few reservoirs like Tarim Jilake Reservoir TII, which has a potential of comprehensive damage of water sensitivity, retrograde condensation and water blocking, and no single technology can solve the problem. Fit-for-purpose measures must be studied to relieve the formation damage and productivity decline in Jilake Reservoir TII. The total salinity of formation water is high (129,239-201,991mg/L) and the water type is CaCl2. (6) The oil & gas wells suffers quick production decline, water production and rapidly rising water content and black oil in some wells
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