Research On The Stages Division And Inner Structure Of Sedimentary Fan Bodies In Dongfenggang Oilfield

The study on the stages division restricted by the division and comparison of isochronous surfaces, and the inner structure of fan bodies such as turbidite fan and delta is not enough for finding new prospecting targets and oilfield exploitation. Take the turbidite fan and delta deposition of Sha-3 upper sub-member and Sha-2 member 8 sand bed set in Che40-44 block--the major blocks of Dongfenggang Oilfield, the stages division and inner structure of two fan bodies are studied to provide guidance for the progressive exploration and development of oilfield.Guided by the theory of stratigraphy and sedimentology, according to core, logging curve, seismic data and development performance data, considering a variety of factors including ectonic, sedimentary characteristics and oil-water relations, controlled by the marker bed, adopting the method of “cyclic correlation and graduation control”, the formation of Sha-3 upper sub-member and Sha-2 member 8 sand bed set is divided into 5 sand bed sets and 34 small layers and then the isochronous stratigraphic framework is established. On the basis of the above mentioned work, 13 phases delta fan bodies are recognized in the 8 small layers of Sha-2 member 8 sand bed set and 30 phases turbidite fan bodies are identified in the 26 small layers of Sha-3 upper sub-member, and then those fan bodies are compared between wells according to the single channel recognition symbols on the basis of the migration and evolution model of fan bodies.Following the division and comparison of fan body stages, the sedimentary characteristics and sedimentary facies of turbidite fan and delta are studied. Most turbidite fans develop channels, which can be divided into three subfacies including inner fan, middle fan and outer fan and further subdivided into 7 microfacies such as main channel, braided stream. Another kind of turbidite fan has no channels, which can only be divided into inner fan, middle fan and outer fan. The delta mainly develops delta front subfacies, which can be divided into 5 microfacies such as underwater distributary channel, mouth bar and sand sheet. Followed by this, the distribution regularity combined with its controlling factors of the turbidite fan and delta are studied. The inner structure of the two fan bodies is studied by the distribution styles and the scale, the microfacies and the lithologic facies characteristics, subsequently, the sedimentary model is constructed. The turbidite fan in the studied area develops on the fault terrace zone of gentle slope in the fault trough lake basin, which has the facies sequence of silty turbidite for its fine grain through long distance transportation. On the basis of the above research, and by the reservoir characteristics study, it is concluded that the reservoir of studied area has medium porosity and low to medium permeability, meanwhile, the distribution of reservoir and its physical properties is controlled by sedimentary facies zone.Finally, the research result of turbidite fan is applied to the oilfield exploration and development as key point. In the exploration, after the detailed study on reservoir development and exploration prospect of the west extended area, the east extended area and the north area, it is concluded that the east extended area and the north area are better than the west one. In the development, the sand body connectivity can be studied by considering the fan body stages.