| The geological reserves calculation is an important part of oil-gas exploration andexploitation, and the reliability of reserves is the foundation in exploration anddevelopment investment, which is related closely to the study of reservoir geology andreserve parameters. With the rapid development of oil industry, a great deal ofrelatively high porosity and permeability reservoirs have been discovered anddeveloped. Nowadays, the focal points of exploration and exploitation have to turn tocomplex reservoirs such as continental low and extra-low permeability oil-gasreservoirs which belong to lithologic or structural-lithological composite oil-gasreservoirs. Therefore, unconventional methods must been used in such challengingreservoirs, especially the study and determination of reserve parameters.With the help of sedimentology, lithology, structural geology, geophysics,well-log geology, reservoir geology, reservoir physics and mechanics of fluid throughporous media, this paper further studies the deposition environment and sedimentarycharacteristics, structural feature, petrological characteristics, trap types and gas-waterrelationship of Xu-4 gas reservoir in CX. By the mean of laboratory experiment,mathematical method and the applied software, core synthetic testing system and themethod of special petrophysical test have been applied to study reservoir physicalproperties, reservoir space characters, water saturation and the mathematical model forvariation of water saturation with physical properties. Based on the combination of thegas permeability under limit production pressure difference and relative permeability,upper limit of water saturation and lower limits of physical properties have beendetermined through the regularity of gas-water two-phase seepage and productivitysimulation experiment under whole simulation conditions. It also calculates proven reserves by using of volumetric method and evaluates it comprehensively.The creative achievements of this article includes:Gas permeability of gas/water bi-phase system at permitted limit productionpressure difference were tested under whole simulation conditions firstly by coresynthetic testing system co-developed by author. Using the method of the gaspermeability trader permitted limit production pressure difference together withgas/water bi-phase relative permeability curve to determine upper limit of watersaturation of clastic rock gas reservoir for the first time. Adopting this method, theupper limits of water saturation in CX Xu-4 gas reservoir is 55％;It's the first-time to test productivity coefficient under different productionpressure difference by whole simulation experiment technology, and adopting limitproduction pressure difference to confirm firstly. The lower limits of porosity andpermeability reaching industrial productivity is 6％and 0.12×10-3μm2;Using data of gas/water capillary pressure, relative permeability, water filmthickness combined with mercury injection data and integrated method to study watersaturation of clastic rock gas reservoir and related mathematical model of expressingwater saturation variation with physical properties, which has been applied to theresearch on lower limits of physical properties and achieved good results;Using secondary oil-gas migration mechanism to study variation and variationallaw of lower limits of reservoir physical properties vertically. The reservoir lowerlimits in different structual region are as follows: the lower limits of pore throat radius,porosity and permeability is 0.074μm, 6％and 0.13×10-3μm2 on the top of the gasreservoir; 0.074～0.148μm, 6～6.6％and 0.13～0.31×10-3μm2 in the middle; 0.148～0.246μm, 6.6～7.7％and 0.31～0.61×10-3μm2 in the bottom, respectively.The research methods and results have been demonstrated in the field, andreserves have been approved by National Mining Reserves Committee.
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