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Commonly when a conventional gas reservoir is produced always the recovery factor expected is between 80-90%, but when the water appears always the plans are subjected to changes, different considerations and several questions raises regarding how the reservoir will be affected. The most common questions are if the recovery factor will be affected, if the current production strategy will change, if we need to consider critical rates per well, if the plateau will change, reserves, production facilities, etc. The presence of water influx can alter the way the gas is produced by the reservoir as the water invades the gas reservoir, the displacement is not 100% efficient (M.Kelkar, 2008). On the other hand it has long been realized that gas recovery from a water-drive gas reservoir may be poor because of high residual saturations under water drive. The Agarwal study (Agarwal, 1965) showed the quantitative potential importance of water influx; its results indicate that gas recovery may be very low in some cases: perhaps as low as 45 per cent of the initial gas in place. So the important fact is that in gas reservoirs with water influx can change drastically the recovery then the expectations, unfortunately, water influx has forced abandonment of a number of gas reservoirs at extraordinarily high pressures, hence the importance to understand the effect of water in the reservoir based on static and dynamic reservoir parameters, and highlight the importance of gas recovery under water drive appears to depend in an important way on: (1) the production rate and manner of production; (2) the residual gas saturation; (3) aquifer properties; and (4) the volumetric displacement efficiency of water invading the gas reservoir. In certain cases, it appears that gas recovery can be increased significantly by controlling the production rate and manner of production. For this reason, the potential importance of water influx in particular gas reservoirs should be investigated early to permit adequate planning to optimize the gas reserves. The methodology presented on this paper appraises the evaluation of four different exploitation scheme, trying to understand and determine the best exploitation strategy using a reservoir simulation model applied to two different reservoirs of the Veracruz Basin with different static and dynamic properties, and quantify the benefits to use the proper one to maximize the recovery factor. A detailed description of each reservoir will be review and results will be compared to emphasis that there is no rules to create exploitation plans for gas reservoirs it will depend on several factors. |
