| Popis: |
Gas wells in tight reservoirs have shown low gas deliverability after drilling and completion operations. This is partially attributed to penetration of completion fluids into the near the wellbore. This increase of liquid saturation into the reservoir can play a significant role in the blocking of tight rock due to high capillary forces and vapor pressure. The scope of this study was to investigate the impact of completion fluids on gas productivity in carbonate and sandstone reservoirs, and to evaluate feasibility of using various solvents to remove and/or minimize liquid blocking effects. In this study, extensive coreflood experiments were conducted on carbonate and sandstone cores recovered from gas reservoirs in Saudi Arabia to assess the loss in gas relative permeability caused by several fluids used as completion fluids. Alcohols were also evaluated as solvents to remove or minimize water blockage. Interfacial tension of fluids was measured using the pendent drop method at reservoir conditions. Experimental results showed that the used completion fluids (brines, KCl, alcoholic brines, and diesel) caused a severe reduction in gas productivity. The clean-up of these fluids was found to be a very slow process and is a function of capillary forces. Neat diesel caused a decline in the gas productivity index (PI) more than brine because it has a lower mobility. The solvents used were effective in displacing the completion fluids studied and consequently restoring gas productivity. Mixing brine with alcohol speedup the cleanup of trapped liquids. |
