Sequence Stratigraphy And Depositional System Research Of Strata Of Eti In A’nan Depression,Erlian Basin

A’nan depression is located in the northeast of Manite depression and is in theA’nan anticlinal structure belt in the Erlian basin. It is one of the largest oil-richdepressions in the Erlian basin group. The target layer is the first member of tenggeerformation of the lower Cretaceous (Et1). The study area is divided into six tectonicunits including Menggulin anticline belt, A’ershan anticline belt, Shannan sag, A’nanslope, and Hanan buried hill and Hadong sag. Based on the logging, seismic,structural characteristics and analytical data, the thesis discusses the sequencestratigraphy and depositional system in the study area. The following conclusionswere made.First, according to the classical sequence stratigraphy, the Et1is divided intolowstand systems, transgressive systems and highstand systems tracts. The lower Et1belongs to the lowstand systems tract, while the upper Et1belongs to the transgressivesystems and highstand systems tracts. By analyzing the systems tracts, the sequencestratigraphic framework is established.Second, according to the analyses of the seismic facies, core and well log, thesedimentary systems are concluded to be barided fluvial delta, fan delta and proximalsubaqueous fan and lake. Within the sequence stratigraphic framework, the spatialdistribution and evolution characteristics of the sedimentary systems are analyzed.During the deposition of the lower Et1, the A’nan depression was shallow waterenvironment. There were many erosion areas, and the sand bodies belong to fan deltaenvironment. During the depositional period of the upper Et1, the water was in highwater level. The mudstone of the deep lake face was deposited in the sag areas. Thefront subfacies of the fan delta were deposited in the southern slope and Menggulinanticline belt. The front subfacies of barided fluvial delta were deposited in thenortheast area, with a long extending.Third, the lower Et1is feldspathic litharenite and the upper Et1is lithic arkose,reflecting that the water gradually deepened and the sediments were long transported.The study of reservoir physical property suggests that the lower Et1are high porosityand low permeability, and the upper Et1are high porosity and medium permeability. Result from lithologic and oil-bearing characteristics analyses show that thefavorable reservoirs are the conglomerate layers of the lower Et1in south slope, aswell as the sand and siltstone layers of the upper Et1in Hanan buried hill.Finally, the distribution of favorable reservoirs is analyzed. The lower Et1has themedium well reservoir characteristic, while the most favorable reservoirs are in thesouth slope. The most and subsequently favorable reservoirs are mainly in Hananburied hill and the area covering the A13well in the north.