Prediction For Favorable Conglomerate Reservior In The Deep Zone Of Daan Fault Depression In South Of Songliao Basin

Daan fault depression is a continuous subsiding fault depression located in the southwest of Songliao Basin.It covers a rear of 1160km2.Until now,there are no well drilled to the deep zone in Daan fault depression.Breakthrough of gas exploration in conglomerate reservoir in deep zone has been achieved in Changling and Yingtai fault depression which are near Daan fault depression.So Daan fault depression has great potential to get gas exploration breakthrough.The research based on the seismic material analysis and the comparision between daan fault depression and other fault depressions which has more information about the deep zone.Regional structure and stratigraphy material are also referred to.The results shows that four formations developed in the deep of Daan fault depression which are upper Jurassic Huoshiling formation,Lower Cretaceous Shahezi,Yingcheng and Denglouku formations upward which features a obvious three-layer structure.A uplift in middle of Daan fault depression divided Daan rift into two part.The north part is a double-fault sag and the south one is a half-graben faulted depression which faulted in the east but overlapped in the west.This structure of Daan rift result in the formation of two hydrocarbon generating center and the north one is larger than the south one.The tectonic evolution of Daan rift can be divided into three stages:faulting period,depression period and wilting period.Fault controlled the sedimentary processes during the faulting period,especially controlled the deposition of Shahezi Formation.The main source rocks of the deep zone of Daan rift is the gas source rocks of Yingcheng and Shahezi Formations.Source rocks in Shahezi Formation covers a area of 950km2 and the thickest place lays in the north sag while that of Yingcheng Formation covers a area of 1300km2 and the thickest place lays in the southeast of the depression.The lithology of reservoirs are mainly conglomerate rocks and seldom are volcanic rocks.The primary pores in deep conglomerate reservoirs are intergranular pores.The existence of acidic volcanic provenance rich in feldspar and the process of feldspar dissolution and laumontitization are the main controlling factors for the formation of secondary pores and fractures.Pore-fracture network formed by the late tectonic action improved the reservoir property.Alluvial fan and fan delta near the controlling fault are the favorable facies for the development of conglomerate.The successive gas breakthroughs show that conglomerate rocks of deep formations is becoming a hot pot for present exploration.According to assessment principles,a favorable reservoir usually occurred near a well developed structure trap andsource rocks,and has conglomerate rocks with good property.Based on these principles,we choose Anshen2 area as a favorable aim target which developed in a nose structure near the west controlling fault in north Daan sag.The source rocks in Shahezi formation is the main source rocks for Anshen2 target and the mud layers in Denglouku and formations above Denglouku performed as cap layer for Anshen2 target.Both of two-dimensional spectrum analysis and ABV absorption shows the gas-bearing features in Anshen2 target.