Research On Seismic Stratigraphy And Exploration Target In The Chanling Graben-depression In Southern Songliao Basin

Recent hydrocarbon exploration of Changling half-grabben depression in Southern Songliao Basin has resulted in a lot of successful discoveries.After about ten deep wells were drille, Dongling gas pool has been found in addition to Dazijing proliferous structural trap. The best production well outputed gas of 200 thousand cubic meters a day. These indicate well exploration prospects this area. And resources hydrocarbon mount is valuated to 0.5 billion ton based on the control of tectonic background or the conferred by the analogy basin, which have the potential to become a big gas field. But Compared to the valuation, the Proved reserves are just 200 million tons. What couses to the results, is the valuation inexactitude? Or is the exploration degree on the low side? Or is the technique not advanced enough for exploration ?or the other reasons, which become a focus problem.Through integrated analysis of depositional facies based on core and seismic data, semi-deep to deep lacustrine facies are confirmed to exist in the graben depression. Dark gray shale with horizontal stratification can be seen on well cores. These shale facies extend tens of kilometeters on well log cross-sections, suggesting extensive distribution of lacustrion deposition. They are replaced by fan-delta with progradation seismic reflections or shallow lacustrine dolomite depositon or beach sands around the depression margin. The seismic amplitude percentages lower than valve values indicate the range of the deep lacustrine facies. Based on the new research results of seismic and depositional facies, the hydrocarbon resources amount is revaluated to be above 0.4 billion. Five prospective gas plays are outlined by means of a method of integral, dynamic and comprehensive basin analysis and synthesis prediction of oil and gas pool formation. The two best ones of them are Darhan fault block and Shuanglong fault block. Compared with the high velocity of the volcanic rocks, the velocity of gas-bearing area is quite lower according to the well log data interpretation and seismic forward model. Gas-bearing volcanic rocks invariably show relative lower velocity, strong amplitude, lower frequency, strong wave attenuation, AVO (far offset amplitudes are larger than near offset amplitudes) and eye-shapeted responses. High gas production wells typically fall on the some small fault zone shown by amplitude shadows on seismic sections.These features are indispensable evidences for us to predict volcanic rock reservoir and locate bore hole targets.