Study On Gas-Water Seepage Mechanism Experiment Of Tight Gas Reservoir In Sulige Gas Field

The Sulige gas field which located in northwestern of Ordos Basin is the largest tight sandstone gas field ever discovered in China. With the deepening exploration and development of Sulige gas field, numerous studies show that the field has strong heterogeneity with low porosity and low permeability, pore complex structure and generally the higher reservoir water saturation. This study is focused on the H8 and S1 formations of Upper Paleozoic Permian,which lies in western and eastern Sulige gas field. The following key findings are achieved:Firstly,through the analysis of the reservoir properties and the microscopic pore structure characteristics shows: the porosity of Sulige gas field is less than 10%, the permeability is less than0.1mD. The cores with the nano and micro capillary pore throat up to 89.6% of total reservoir cores,this kind of core in the process of seepage plays a vital role and it determines reservoir type.Secondly,combined the nuclear magnetic resonance experiment technology with stepwise pressurize gas drive experiment technology to study the minimum displacement pressure when residual water began to flow. With the increase of displacement pressure, movable water change has its own rules. From the experiment,we can learn that:residual water exist in the small pore,movable water exist in the large pore. Compared with the movable water,residual water make up a large proportion of the cores with a small permeability and porosity. Gas drive pressure and rock physical property directly affect the water saturation change rule of the cores.Thirdly,there are actuating pressure gradient in the tight sandstone gas reservoir which containing water and has a low permeability. Discussing two main method that measure the actuating pressure gradient,considering non-darcy seepage theory,using a new way to measure and study the actuating pressure gradient pressure,at the same time,caculating effective drainage radius and having a dynamic simulation about producing reserve. The experimental results suggest that:(1)For the gas reservoir that has a low water saturation,the permeability will greatly affect the well control reserves only within a certain range,when the effective drainage radius reached its physical boundaries,the permeability will never affect the well control reserves.(2) Effective drainage radius will affect the the relationship between gas permeability and water saturation. The lower gas permeability,the higher water saturation,the smaller effective drainage radius.(3)The original water saturation can affect the effective drainage radius more than the permeability. With the increase of the original water saturation,the drainage radius reduced.