Study On Hydrocarbon Accumulation Conditions In The First Member Of Shahejie Formation On Southern Slopes Of Qikou Sag

Qikou sag is the biggest source rock sag in Huanghua depression. It has plentiful oil and gas reserves, with large remaining hydrocarbon resources. It is one of the oil-rich sags with the most extensive exploration prospect. Many types of oil and gas reservoirs have been found. It is the focus of oil and gas exploration at present and even in the future. By studies and practice in the past few years, great breakthroughs have been obtained in stratigraphic-lithological hydrocarbon reservoirs exploration in the first member of Shahejie Formation(Es1) in southern Qikou Sag. The exploration degrees in various slopes are becoming higher and higher, which means that the deep studies on hydrocarbon accumulation conditions in Es1 on southern slopes of the Qikou Sag have great practical significance for guiding exploration deployment in southern Qikou Sag. So it is the main purpose of setting up this subject to study the oil and gas reservoir forming condition of the Es1 in the southern slope of the depression.Based on seismic and logging data, we use the sedimentology, sequence stratigraphy and petroleum geology theory as a guide. And we use the tectonic evolution analysis and paleotopography restoration technology, sequence stratigraphy interpretation technology, seismic facies and comprehensive research technique of sedimentary facies, stratigraphic and lithologic trap identification technology and comprehensive evaluation technology to carry out evolution characteristics of structure, fault distribution and the tectonic evolution of the southern area of Qikou Sag.We establish the stratigraphic framework according to the results of well-seismic combination and accurate calibration and interpret the regional third-order sequence and the forth-order sequence of the Es1 to study the distribution of the Es1 formation and to restore the ancient landform and sedimentary environment and to analyze the change law of sedimentary pattern and different sedimentary facies belts, and to define the favorable reservoir development zone. We carry out the oil and gas accumulation conditions and analysis of hydrocarbon source rock, reservoir, caprock, and reservoir cap assemblages’ characteristics, and make the matching rules of oil-gas migration, accumulation and preservation clear. And we carry out the main control factors of oil and gas enrichment and accumulation pattern to make find the favorable pre exploration belt. We use the implementation of structural traps, the prediction of the lithologic stratigraphic traps and the reservoir prediction and faults detection to study the favorable areas. We carry out the comprehensive geological evaluation and oil and gas detection to find the favorable drilling target and finally propose the exploration deployment.In this paper, through studying the structural features and the formation and evolution of the southern area of Qikou Sag, we know that the Shahejie formation is a typical faulted lacustrine basin depositional environment. There are three major slope areas in the southern part of southern area of Qikou sag. The Qinan and Qibei slopes are simple inclined slopes that were formed by differential basin settlement at the Es1 period. The Chengbei fault step is a step shaped slope mainly affected by multi period fault activity.Through the application of stratigraphy, we establish the third and the forth order sequence stratigraphic framework in the southern areas of Qikou Sag. The southern areas of Qikou Sag developed braided river delta front sandstone reservoir and carbonate reservoir in Es1 depositional period. Proven oil and gas are mainly developed near the large fault and unconformity surface. This area mainly develops structure-lithologic reservoir. Fine description technology series of stratigraphic lithologic traps is the best method to implement lithologic traps. The migration of oil and gas is mainly through the fault, unconformity and effective permeability. The oil and gas reservoir in the low slope is mainly controlled by the faults and the Stratigraphic lithologic trap developing zone. The oil and gas reservoir in the middle-high slope is mainly controlled by the unconformity and stratigraphic and lithologic pinch out zone. There are two oil and gas accumulation period which are match well with the tectonic activity and the formation period of Es1 traps. At the end of this paper, through combing the current exploration situation of southern Qikou, we optimize the three favorable exploration areas, and prepare a batch of advantageous drilling target. It plays a guiding role in the exploration of the southern part of the Qikou sag.