An experimental study on microscopic characteristics of gas-bearing sediments under different gas reservoir pressures

Gas-bearing sediments are widely distributed in five continents all over the world.Most of the gases exist in the soil skeleton in the form of discrete large bubbles.The existence of gas-phase may increase or decrease the strength of the soil skeleton.So far,bubbles’structural morphology and evolution characteristics in soil skeleton lack research,and the influence of different gas reservoir pressures on bubbles are still unclear.The micro characteristics of bubbles in the same sediment sample were studied using an industrial CT scanning test system to solve these problems.Using the image processing software,the micro variation characteristics of gas-bearing sediments in gas reservoir pressure change are obtained.The results show that the number and volume of bubbles in different equivalent radius ranges will change regularly under different gas reservoir pressure.With the increase of gas reservoir pressure,the number and volume of tiny bubbles decrease.In contrast,the number and volume of large bubbles increase,and the gas content in different positions increases and occupies a dominant position,driving the reduction of pore water and soil skeleton movement.

Reservoir accumulation conditions and key exploration&development technologies for Keshen gas field in Tarim Basin

The Keshen gas field is located in the central part of Kuqa foreland thrust belt in Tarim Basin,and is another large gas field discovered in Kuqa depression after Kela 2 gas field.Since the breakthrough in 2008,a number of large and medium scale gas reservoirs including Keshen 2,Keshen 5 and Keshen 8 have been discovered,that are characterized by ultra depth,ultra-high pressure,ultra-low porosity,ultra-low permeability,high temperature and high pressure.With natural gas geological reserves of nearly trillion cubic meters and production capacity of nearly 5.5 billion cubic meters,the Keshen gas field is the main natural gas producing area in Tarim Oilfield.The Keshen gas field is located in a series of thrusting imbrication structures in the Kelasu structural belt of Kuqa foreland thrust belt.The salt roof structure,plastic rheology of salt beds and pre-salt faulted anticlinal structure constitute the large wedge-shaped thrust body.The thick delta sandstone of the Cretaceous Bashijike Formation is widely distributed,and it forms the superior reservoir-caprock combination with overlying Paleogene thick gypsum-salt bed.The deep Jurassic-Triassic oil and gas migrate vertically along fault system formed in Late Himalaya,break through the thick Cretaceous mudstone and move laterally along the fracture system of the pre-salt reservoirs,to form anticline and fault anticline high pressure reservoir groups.Through near ten years of studies,the three-dimensional seismic acquisition and processing technology for complex mountainous areas,extrusion salt-related structural modeling technology and fractured low-porosity sandstone reservoir evaluation technology have been established,which lay a foundation for realization of oil and gas exploration objectives.Logging acquisition and evaluation technology for high temperature,high pressure,ultra-deep and low-porosity sandstone gas reservoirs,and efficient development technology for fractured tight sandstone gas reservoirs have been developed,which provide a technical support for efficient exploration&development and rapid production of the Keshen gas field.