Tight gas reservoirs represent a significant portion of natural gas reservoirs worldwide. Production at economical rates from tight gas reservoirs in general is very challenging not only due to the very low intrinsic permeability but also as a consequence of several different forms of formation damage that can occur during drilling, completion, stimulation, and production operations. Tight gas reservoirs generally do not produce gas at commercial rates, unless the well is completed using advanced technologies and efficiently stimulated.Well productivity in tight gas reservoirs is largely controlled by formation damage mechanisms such as liquid invasion damage into the low permeability rock matrix that reduces the near wellbore permeability as a result of temporary or permanent trapping of liquid inside the porous media. In many cases of tight gas reservoirs, the key factors that control well productivity and formation damage mechanisms are not well understood, since it is challenging to characterise them in tight formations.This paper presents evaluation of damage mechanisms and characterization of dynamic parameters in tight gas reservoirs and proposes the methods that can provide improved well productivity by minimizing damage to the tight formation. Numerical reservoir simulation is integrated with tight gas field data analysis and core flooding experiments to better understand the effect of different damage mechanisms on well productivity in order to propose the possible remedial strategies that can help achieve viable gas production rates from tight gas reservoirs.
The low permeability and tight gas reservoirs are problematic throughout of their development (drilling, completion, stimulation and production) around the wellbore. However, they required advanced improvement techniques to achieve flow gas at optimum rates. Phase Trapping or retention of fluids is a form of mechanical formation damage mechanism, which is caused by fluid invasion into formation, and also when liquid leak-off into formation during fracturing stimulation near the wellbore. Low permeability and tight gas reservoir are sensitive to water invasion damage results create water blocking and phase trapping damage due to high critical water saturation, relative permeability effects, capillary pressure and Interfacial tension between produced fluid and wellbore fluid. Proper evaluation of damage and its factors which influenced its severity is essential for prevention and optimizing well productivity. Thus, this study is presenting both laboratory experiments and simulation to evaluate phase trapping damage. In which, the core flooding was performed to evaluate permeability damage by using Malaysian diesel-oil drilling fluid in comparison with water based drilling fluid. Further, interfacial tension was tested between produced gas and wellbore fluids at different temperature and pressure conditions. The effect of interfacial tension on phase trapping damage was observed and validate with the result of core flooding experiments where the affect of water injection and diesel-oil injection on core permeability was studied and shown. Reservoir Simulation approach was also used to study the effect of relative permeability curves on phase trapping damage and its impact on well productivity. The result highlights the benefits of using Malaysian diesel-oil in drilling and fracturing the low permeability and tight gas reservoirs in meaning of 30% increment in well productivity compared with water based fluid.
Tight gas reservoirs represent a significant portion of natural gas reservoirs worldwide. Production at economical rates from tight gas reservoirs in general is very challenging not only due to the very low intrinsic permeability but also as a consequence of several different forms of formation damage that can occur during drilling, completion, stimulation, and production operations. Tight gas reservoirs generally do not flow gas to surface at commercial rates, unless the well is completed using advanced technologies and efficiently stimulated. One of the major damage mechanisms in tight gas reservoirs is liquid phase trapping damage that is controlled by pore system geometry, capillary pressure, relative permeability and interfacial tension between the invading trapped fluid and reservoir fluid. The liquid invasion damage into the rock matrix reduces the near wellbore permeability as a result of temporary or permanent trapping of liquid inside the porous media, and results in low productivity in tight gas reservoirs. This study presents evaluation of damage mechanisms in tight gas reservoirs and the methods that can provide improved well productivity by minimizing damage to the formation. Numerical reservoir simulation is integrated with tight gas field data analysis and core flooding experiments to better understand the effect of different damage mechanisms on well productivity in order to propose the possible remedial strategies that can help achieve viable gas production rates from tight gas reservoirs.
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