| Primary reservoir space and percolation path in gas reservoirs of middle Permian in Weiyuan-Ziliujing structure belt is karst cavity or fracture, tectonic fracture which was generated in the course of wrinkle played a key role in connecting with reservoir, the heterogeneity is strong in reservoir, There is no waters in block together and no unified gas-water interface, many wells have the characters of coexistence between gas layer and water layer, and the relationship between gas and water is not clear. So the gas-water relationship is complicated, which has entered the exploitation of gas reservoir is difficult.Based on the date of drilling, logging , well logging, testing and production performance, and combined with previous works, this article emphatically analyze the character of reservoir ,output of liquid, distribution of gas and water ,gas-water relationship, construe the source of energy in the area of having vast water-yielding and active water body ,analyze the state of gas and water occurrence,evaluate range of profitability in remaining reserves distribution area. Through above research, get the main recognition as follows:1. High-productivity well mainly distribute along highland of both sides in karst region of Weiyuan structure, gas well mainly distribute along the fault in Ziliujing structure. Reservoir water salinity is higher in Reservoir of Middle Permian of Ziliujing structure, because the depth of burial is deeper and vaporization result in water inspissation, content of mineral ions is relatively high in karst region .reservoir water salinity evidently decline on the both sides of karst region.2. Theoretically, isolated gas could be exploited through the method of drainage for finding gas in water produced of gas wells. But in practice this method is difficult to be achieved, this is because of limitation of geological condition and failed measure of artificial drainage.If the connectivity of reservoir between wells is poor, drainage in the low position well sometimes difficult to slow down the water invading to high position well. At the same time, if we take the measure of controlling water yield when gas well begin to produce water, this will result in gas well be drowned, and also lead to reservoir waterlogging in large area .Even if water could return to formation after well be long-term shut down in the later period, it is difficult to restore production.3. Main drive energy in water-bearing gas reservoir is come from isolated gas. There is no unified gas-water interface in most cavity-fracture system. Factors of leading to producing water in gas well include permeability of reservoir; location of producing pay in perforated well, volume of isolated water and gas, produce measure.4. According to the reserves which is worked out by material balance method and cumulative oil production method, recovery percent is lower generally in Weiyuan structure, but is higher in Ziliujing structure which recovery percent is above 70 percent, meanwhile, base on production data before August of 2009, the calculated reserves in Z2 well is 50.759×108m3, The remained reserves is 2.133×108×108m3, preliminary estimates Z2 well could continue product for 10 years.5. Aim at the region where remaining reserves is abundance, propose to carry on testing and exploiting in no tested reservoir of middle Permian in W39 well and W68 well, and suggest disposing new wells in the zone of W29-W83-WY36 and W43-W2-WY2. |
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