Sedimentary Evolution Of The Lower And The Middle Of The Sha 3 Member In The Gunan Sag

Gunan Sag is a subunit sag of the Zhanhua Sub-depression of the Jiyang Depression. And it is 150km2. There is an abundant oil and gas zone around the sag, but there is a little research on it. And therefore, it is important to study sedimentary evolution of this part. Based on the theories of sedimentology, petrology and geology, with the analysis of geology, well log and seismic data, the lower and the middle of the Sha 3 Member of Gunan sag were divided carefully into the units of member and sand group. On the basis of the isochronous stratigraphy framework, the depositional system was researched carefully, and the sedimentary evolution was summarized.Now, the accuracy of strata correlation of the lower and the middle of the Sha 3 Member in the Gunan Sag was only divided into the unit of member. This paper divided accurately the strata of the lower and the middle of the Sha 3 Member. In order to make correlation units of target stratum more delicately, 14 interfaces, which can ensure the age contrast precision, were identified to classify 13 sand groups for the first time, and the vertical and horizontal distribution and evolution characters were analysed. These works of building the isochronous stratigraphy framework raised the research level of target stratum of the Gunan Sag.Till now there is no whole research on the sedimentary evolution in the Gunan Sag. Adopting the latest theoris and methods of modern sedimentology, and combining the data of cores of 10 wells, log, seismic data, and former research results,the following works were done. The marks of sedimentary facies were researched from three aspects: lithology, sedimentary structure and electrofacies. 5 types of sedmentary facies were identified. 5 pieces of single well facies were done. (3 classic wells of them were introduced in this paper. ) 7 cross sections of sedimentary facies-3 crossline and 4 inline-were done. (3 classic cross sections which prong the most important area in the NE part of the Gunan Sag, were introduced in this paper. ) The sedimentation model of detal-fan detal-storm was built and expounded. The distribution of sedimentary facies of every grade of target stratum were blocked out and clarified. And this paper analysed sedimentary evolution of target stratum in detail and gained the follow recognition:â‘ In the lower of the Sha 3 Member deposition period, the lake basin subside fast, and the lake enlarged repaidly. The water was deep. And the souce was inadequate. The condition of deposition was underfilled. Some small deltas and fan deltas were developed from 3 directions: the east side of the Gunan Fault, the Kenli Uplift and the Kendong Uplift. They shrinked with the enlargement of the lake.â‘¡In the middle of the Sha 3 Member depositionperiod: The souce got rich stronger. The lake shrinked. The sediment from 3 areas-the Gunan Uplift, the Kenli Uplift and the Kendong Uplift-developed the sedimentary system delta-fan delta-storm in the lake. The sources came from three areas: the Gudao Uplift-WN, the Kendong Uplift-NS and the Kenli Uplift-South.