Study On Sequence Stratigraphy And Forecast On Subtle Trap Of Zhu Ⅰ Depression In Paleogene

ZhuⅠDepression is located in the northern part of the Pearl River Mouth Basin, and it is the most abundant zone of oil and gas accumulation and distribution in the South China Sea Basin. ZhuⅠDepression has two-tier structures in Paleogene.One is a fault depression in earlier stage and a depression in later stage, the other is marine strata deposited after continental sedimentary strata. It has unique tectonic frameworks and complex development histories. Its infrastructural layers have the basic pattern of extensional-share, echelon episodic rift structure, so ZhuⅠDepression have the structural features being many low-lying lands and upthrows which has a basic structural units of half-graben. Complex half-graben is the core concept of faulted structure in Paleogene of ZhuⅠDepression, and it is a oil-generatied accumulational unit which has a unique structural property and sedimentary response. Infrastructural layers of ZhuⅠDepression has potential to explore oil and gas.Based on the integrated analysis of cores, well logging, seismic data and other basic data, the sequence stratigraphy and the depositional systems of Paleogene of ZhuⅠDepression are studied. The paper emphasize the crucial role that the structure played on forming of stratic boundary and sequence internal filling of the basin. Begin with the whole ZhuⅠdepression, the structure controlling the depositional system, and the applications of the principle theory of sequence stratigraphy, the paper analyses the function of the basin-controlled fault to the sequence architecture, the lateral transfer zone to the provenance orientation and the paleostructure and the paleotopograhy to the sands distribution , and discusses on sequence stratigraphy model and distributed and evoluting rule of the depositional systems and in sequence strata shelf in downfaulted basin.The evolution of ZhuⅠDepression has undergone five major tectonic movements from Mesozoic to Cenozoic, and not only has transformed the existing depositional environment, but also has determined the deposition of the new style. Tectonic movements are the main factor to impact the sequence evolution of continental basin, which directly determines the formation and dying out of the basin’s accommodation. The episodic, periodic and fluctuant characteristics of tectonic movements directly control the multi-cycle characteristics of sequence and the evolutional phases of internal sequence. It is the main performance of deposit control on which construction act of ZhuⅠDepression in Paleogene that is it, because of the uplift of tectonic movements, resulting in serious erosion of late Wenchang and Enping Group stratigraphy. Distributional characteristic of tectonic movement result in differences of erosion degree in each seg and regional otherness of depositional characteristics.ZhuⅠDepression set up uniform isochronic Sequence stratigraphic correlation framework on the base of the analysis of tectonic-sedimentary evolutional history.The sequence of Paleogene is two 1st order sequence, and which can be divided ulteriorly into three long-term base-level cycles (second-order sequences) and 8 intermediate-term base-level cycles (third-order sequences). The sequence stratigraphic framework was established, and determine their boundary. In the case of scarce drilling and poor seismic data quality, the third-order sequences as a unit to carry out the study on areal distribution of sedimentary facies and sequence stratigraphic configuration of ZhuⅠdepression in paleogene.And summed up its distributive regular pattern and its spatial and temporal evolutionary characteristic. The paper establish depositional model of fault depression and fault sag regard half-graben as the basic structural unit. On this basis, the paper anatomically study the sedimentary characteristic of key sags.Depart from macro petroleum geology conditions, the article analyses s the basic condition formed subtle trap in ZhuⅠdepression . Analyses the reservoirs distribution by integrated utilizing generated condition of reservoir and predicts the advantageous subtle traps, provides a theoretical and scientific basis to the subtle reservoir exploration in ZhuⅠdepression. Studying, summed up the six common types of subtle trap in the pull-apart basin, Comprehensive analysis of the source bed reservoir and overlying formation, forecasted the favorable zone of subtle reservoir in ZhuⅠDepression.