| Exploration and development of oil and gas fields, the calculation of reserves and economic evaluation are inseparable from the identification and evaluation of the lower limit of reservoir properties. With the discovery of a new oil and gas fields, you must first study and determine the lower limit of reservoir properties. With the continuous improvement of the exploration and development, faced with a situation of gradual reduction of oil and gas resources, it is necessary to re-evaluate the lower limit o f reservoir propertieson. With the development of science and technology, the continuous improvement of the development level, evaluation and analysis of the lower limit of reservoir properties should be identified to calculate of the back-up reserves of oil and gas field under the new situation.Sulige gas field is located on the northwest side of Shaanxi slope in the Ordos Basin. The exploration area of Eastern Sulige gas field is about11000km2, which is a large area of sandstone lithologic gas reservoirs. The reservoir is with characteristic of typical multi-layer gas system. He8, Shanl and Shan2Members are the main producing formation. The lower limit of reservoir properties of Eastern Sulige gas field may be high.Therefore it is necessary to re-evaluate the lower limit of effective reservoir. The newly proposed lower limit of reservoir properties is able to get validation of the dynamic data of gas field development in Eastern Sulige gas field.This study analyzes the reservoir geology and characteristics of tight sandstone of Upper Paleozoic in Eastern Sulige gas field, including lithology, physical features, spatial characteristics, as well as electrical characteristics of the reservoir. The lower limit of effective reservoir in Eastern Sulige gas field is studied by using the statistics law, logging parameters crossplot method, mercury intrusion data analysis, minimum flow pore throat radius, the gas-water relative permeability data analysis method to calculate the lower limit of reservoir physical properties. Capacity simulation and production analysis, as well as comprehensive analysis of the main controlling factors are studied to verify the lower limit of reservoir physical properties.Based on the research of reservoir characteristics of Upper Paleozoic in Eastern Sulige gas field, deepen the understanding of the lower limit of effective reservoir, the following conclusions are obtained:Tight sandstone reservoirs of Eastern Sulige gas field have low porosity and low permeability. The average porosity is8.64%and average permeability is0.304×10-3μm2. Physical properties of lower submember of member8of Shihezi formation are better than that of upper submember of member8of Shihezi formation.Physical properties of Shan2members are better than that of Shanl members. The rock types of He8and Shan1member are mainly medium-coarse-grained lithic quartz sandstone and lithic sandstone, as well as those of Shan2member are mainly medium-coarse-grained lithic quartz sandstone and quartz sandstone. The average content of interstitial material is between15.1%and16.1%. Shihezi Formation has a higher content of illite/montmorillonite interlayer and chlorite, Shanxi Formation and Taiyuan Formation has a higher content of illite and kaolinite. The reservoir experienced a strong diagenesis transformation, primary intergranular holes basic disappeared, secondary dissolution pores, and intergranular pores of clay minerals remian as the main reservoir space.The reservoir porosity of He8member is slightly better than Shanl and Shanl members. Throat is mainly sheet/bend sheet and tube-like.By doing the research of the lower limit of reservoir characteristics of Upper Paleozoic in Eastern Sulige gas field, we can draw the following main constructions. The lower limit of porosity of He8member is5.0%and penetration rate is0.1×10-3μm2.The lower limit of porosity of Shanl member is4.0%and penetration rate is0.08×10-3μm2. The lower limit of porosity of Shan2member is3.5%and penetration rate is0.075×10-3μm2. |
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