关键词: 特低渗储集层, 物性下限, 电性下限, 生产压差, 渗透率, 毛细管压力, 岩电实验

Abstract:

The low to ultra-low permeability reservoirs in the DF A and WC X/Y blocks, western South China Sea, are characterized by complex microscopic structures, making it difficult to understand the lower limits of reservoir physical and electrical properties. Through core single-phase displacement experiments under various pressure differences, and core capillary pressure-lithoelectric experiments at high temperature and high pressure, the lower limits of porosity, permeability, saturation, and resistivity of these low to ultra-low permeability gas reservoirs were examined. On this basis, the variations of the lower limits of these reservoir properties were discussed. The results show that the cores obtained from the gas reservoirs in the DF A block have the physical properties which are positively correlated with gas flow rate, and the cores from the ultra-low permeability gas reservoirs in the WC X/Y block exhibit very low gas flow rate, which couldn’t be improved significantly as the pressure difference was increased. In the presence of irreducible water, as the differential pressure for production increased, the lower limits of porosity and permeability of cores from both blocks declined gradually. As the physical properties of the reservoirs improved, the upper limit of water saturation became lower. As the reservoir physical properties improve, the cores from the DF A block demonstrated an increasing lower limit of resistivity, while the cores from the WC X/Y block reflected a decreasing lower limit. It is supposed that the reason should be attributed to different pore structures and fluid occurrence states of the reservoirs.

Key words: ultra-low permeability reservoir, lower limit of physical property, lower limit of electrical property, producting pressure difference, permeability, capillary pressure, lithoelectric experiment