1 Northwest Branch,Research Institute of Petroleum Exploration & Development,PetroChina,Lanzhou,Gansu 730020,China;
2 Research Institute of Petroleum Exploration & Development,Tarim Oilfield Company,PetroChina,Korla,Xinjiang 841000,China
Abstract：Sedimentary environment and fracture are the master factors in areas of Well TZ 45 and Well ZG 8 of North Slope of Tazhong.The carbonate reservoir in Lower Ordovician Yingshan Formation could be divided into four types: hole type,fracture type,fracture-hole type and cavernous type.These types of carbonate reservoirs present strong bead-shaped reflections on seismic sections and seismic reflection patterns could be classified as layered reflection,dotted reflection and faulted reflection.Our petrophysical analyses and prestack AVO modeling indicate that P-Wave impedance and density are the most sensitive to reservoir response.The reservoir characteristics in Lower Ordovician Yingshan Formation are low wave impedance and low density.When the reservoir contains oil and gas,far offset amplitude is stronger than the near offset amplitude,and it correlates to high fluid factor and positive and negative abnormal on P·G attribute profile.When the reservoir contains water or mud,neither the far offset amplitude nor the near offset amplitude do not change significantly.Fluid factor is low,and P·G attribute profile shows only negative abnormal.Reservoir prediction has been improved by predicting the reservoir distribution with prestack elastic parameter inversion,and the fluid characteristics with prestack AVO analysis.
