The Water Blockage Effect on Desiccated Tight Gas Reservoir

摘要

Increasing world demand on energy has encouraged the development of natural gas resources from a variety of sources. Tight gas is a major gas resource which accounts for 14% of the total gas resources in the world, including conventional systems (Total, 2012). Water blockage is considered a potential damage issue in tight gas reservoirs and motivated the initiation of this study. A tight gas reservoir is a low permeability reservoir of less than 0.5 md which tends to have higher capillary pressure and higher irreducible water saturation than a conventional reservoir. Tight gas reservoirs also have smaller grains which signify the effect of water film around the grains on gas flow. The gas relative permeability in tight gas formations becomes more sensitive to liquid saturation due to the nature of its grains. As some of these reservoirs show conventional-like connate water saturation, this led to a hypothesis that these reservoirs have gone through a desiccating process and reduced the connate water saturation to a lower value than the irreducible value. The objective of this study is to examine if water blockage is a potential issue by generating relative permeability curves and simulating different production cases with different water saturation settings. By looking at the well performance and water and gas recovery in these situations, a new understanding of tight gas performance is achieved. The method used included creating a simulated generic model and setting the water saturations at different settings to see the effect of injecting water during drilling and hydraulic fracturing. Two cases with open flow and fixed downhole pressure were discussed this paper. The results show an effect on gas production by delaying production by 21 years in the open flow situation. The gas production is reduced up to 17.17% in the open flow mode. In addition, cases with different water saturation settings never recovered all of the injected water, and in fact, the degree of recovery is proportional to the degree of desiccation.