Experimental Study On Seepage Characteristics Of DH Low Permeability Gas Reservoirs

Low permeability gas reservoirs are different from conventional gas reservoirs, because of their characteristics of low porosity and low permeability, the percolation characteristics of low permeability gas reservoirs are quite different from that of conventional gas reservoirs. The average permeability of X3 layer in DH gas reservoir is 2.05mD, which belongs to the low permeability reservoir. The average permeability of X4 layer and X5 layer is 0.068mD, and the average permeability is 0.1 mD, which belong to the special low permeability reservoir, the fluid flow in the reservoir has a unique percolation mechanism. This article mainly uses indoor physical simulation method, respectively for the gas reservoirs are the main producing layer X3, X4 and X5 layer to carry out the single-phase flow and two-phase flow, as well as water lock effect mechanism of, provide the mechanism and basic parameters for the design of the gas field development plan.To this end, the focus of the study includes (1) Aiming at the low permeability layer of the target gas reservoir, the low velocity percolation test of 20 cores of single phase gas was carried out, and the effect of the slip effect on the low permeability gas reservoir was studied. (2) Use laboratory developed abnormal high pressure core flooding for device (200?, 200MPa), in the real geological conditions to carry out the seven core stress sensitivity test (174.2?,95.7MPa), research in the development process of gas reservoir pressure drop caused the permeability stress sensitivity. (3) With the decrease of formation pressure, water flooding phenomenon occurs, which causes the gas and water two-phase flow. According to the seepage characteristics, firstly, we establish a high temperature and high pressure water flooding gas phase permeability test method, after then, under the two conditions of normal temperature and high pressure and high temperature and pressure (151.8?174.2? 37.12?54.1MPa), the water flooding gas phase permeability curves of the 8 groups were tested. (4) When switching well in actual gas well, the near well area is easy to produce high water bearing saturation zone, which causes the phenomenon of water lock, in order to evaluate the degree of water lock effect, we have established a new method to test the water lock effect and the starting pressure of water lock (patent pending), and we carried out the water lock damage test of the 6 groups of cores.The main conclusions are as follows:(1) The critical pressure of the DH gas reservoir is less than 0.125MPa, and the waste pressure should be higher than that of the general gas reservoir, so the gas slippage effect can not be considered in the actual production; (2) DH gas reservoir X3 layer stress sensitive average medium weak, the other two layers of medium to strong, and the stress sensitivity of conglomerate is generally stronger than that of sandstone, and the low permeability sandstone is higher than high permeability sandstone that of Sha Yanqiang; (3) Compared two conditions of high pressurem high temperature and atmospheric pressure water drive gas relative permeability, the average irreducible water saturation is lower than 3%, the left displacement of the seepage point is about 8%, the water drive efficiency is low 6?8%, and the residual gas saturation is about 5%, it can be found that they are very different; (4) Experimental results of water blocking display DH gas reservoir water lock effect after the occurrence of the gas phase permeability decreased 10?20%, water vapor lock releasing start pressure between the 0.3-3.7MPa but core experiments have been shorter, so start pressure gradient, water lock lift lock water is very difficult.