Deep-water Gravity Deposits In Songliao Terrestrial Basin

Since1970s, deep-water sedimentation has become the most active field ofhydrocarbon exploration and study in continental margins and terrestrial basins.Currently latest research progress in deep-water sedimentation can be briefly summedup as follows:①the find of deep-water traction flow;②traditional turbidity currenttheory has been challenged and questioned;③deep-water sedimentation patterns arebecoming increasingly perfect;④Mass transport deposits（MTDs） has been animportant exploration field of deep-water deposition;⑤deep-water mud and shale hasbecome a new exploration domain of unconventional reservoirs.Based on comprehensive analysis of the cores, logs, tests, seismic data and so on,combined with the last worldwide research progress of deep-water gravity flows, thisdissertation systematacially studied sedimentary features, identification marks,distributary patterns, and morphology of gravity flows in the large lacustrine depressionbasin in K2qn of the western slope break in Songliao basin.This study is of both regional and universal significance and provides thefollowing new insights:1. Single and multi-grade slope breaks were developed surrounding thedepression center. This dissertation studied the negative geomorphic units ofvalley systems, fault troughs, fault slops for the first time.Slope breaks and physiognomy are an important factor to control the transportion,deposition process and discharge of lacustrine sand bodies and gravity flow. Singleand multi-grade slope breaks were developed surrounding Songliao depression center.According to the causes of the valleys, the valleys of the slope-break belts weredivided into three types: the incised valleys, the troughs which were formed at thedownthrown sides of the syndepositional faults and the extensional fold valleys.2. It was the first time discovery of MTDs in terrestrial basin, MTDs may bea new exploration and development target in terrestrial basin. MTDs which were composed chiefly by sandy debris-flows mixed with a little ofslide and slump are the major type of the gravity flows in Songliao basin. The sandydebris in MTDs can be favorite reservoir due to their thick monolayers, good physicalproperties and the wide distribution. On the seismic sections, the thick MTDsmanifested weak amplitude, chaotic and mound seismic reflection configuration.Erosion linear groove were found at the bottom of the MTDs. The turbidite in thestudy area is thin and just has low exploration value.3、The landform of the slope breaks and the valleys played a significantcontrolling role in the morphology of MTDs. Large scale troughlike and fault pitMTDs were discovered for the first time.The morphology of MTDs was importantly controlled by the negative landform ofthe fault-trough and fault pit at synsedimentary grabens, incised valleys and theextensional folds. On the simple slope breaks, the sublacustrine fans and mother-childfans were developed, slide distances of the gravity flows were proportional to thegradients. Fault-pit gravity flows were ribbon shape parallel to the shoreline. The sandbodies of the trough-gravity flows were long, narrow, straight, oblique to the shoreline,and not fan shape. The troughlike morphology were controlled by incised valley,extensional folds, negative geomorphology.