Relationship between Tight Sandstone Reservoir Formation and Petroleum Charge in Dabei Area of Kuqa Foreland Basin

The tight sandstone reservoirs below the salt and gypsum unit in the Dabei area of the Kuqa foreland basin are characterized by deep burial, low porosity and permeability, which produce natural gas and minor light oil. The relationship between tight sandstone reservoir formation and petroleum charge in the Dabei area of the Kuqa foreland basin are studied by combining the porosity evolution of the tight sandstone reservoirs based on the analysis the tight sandstone reservoirs characters, natural gas and light oil maturity, and petroleum charge history. The pore space of the tight sandstone reservoirs below the salt and gypsum unit in the Dabei area are dominated by secondary intergranular dissolution pores, most of which are filled by bitumen and have an excellent interconnectivity. Strong compaction is the important cause for the development of the tight sandstone reservoirs and carbonate cements should form before the Kuqa formation deposition to cause the porosity decreasing. The presence of widespread bitumen observed in the K₁bs tight sandstone reservoir, organic geochemistry characters of light oil and gas, results of fluid inclusions investigation indicate that there had been two episodes of oil and one episode of gas charge in the tight sandstone reservoir. The late episode of oil charge identified in the tight sandstone reservoir is estimated to be at around 5-4 Ma, responding to the beginning of Kuqa formation deposition. The timing of the natural gas charge is estimated at around 3-2 Ma and are belong to the period of the uplift and erosion. The tight sandstone reservoirs below the salt and gypsum unit in the Dabei area of the Kuqa foreland basin have shallower burial deep and higher porosity during the period of oil charge than natural gas charge because the sandstone reservoirs had experienced strong compaction and cause the formation of tight sandstone reservoirs.