Sedimentary Facies Of The Qixia Formation And The Maokou Formation In The Northwestern Sichuan Basin

In this paper,the Qixia Formation—Maokou Formationtion in Northwestern Sichuan Basin is focused as the research object.Based on predecessors' research,combined with key outcrops' observation,slice identification,analysis of related materials about well drilling&logging and porosity-permeability data,as well as investigation of the regional tectonic setting and the lithofacies palaeogeographical environment,Qixia Formation—Maokou Formationtion's stratigraphic feature,sedimentary facies and reservoir' s characteristics are summarized.In the study of the stratum,the layers color,thickness,attitude,structure,contact relationship,depositional cycle and paleontology are so important to study the stratigraphic feature.By analizing the relationship between lithology and electric property revealed on several wells' logging curvers,characteristic of the important geological boundary in Qixia Formation—Maokou Formationtion are confirmed.And then,the geological boundary would guide the stratigraphic classification and contribute to the research of stratigraphic distribution.In the study of sedimentary facies,the main types of sedimentary facies of Qixia Formation—Maokou Formationtion is considered to be the gentle slope type platform with a special platform edge,which could be divided into 4 kind of subfacies containing platform edge,shallow gentle slope,deep gentle slope and slope—basin.According to the different characteristics between 4 kind of subfacies,Qixia Formation—Maokou Formationtion's sedimentary subfacies in typical outcrops and wells could be divided,and be compared towards vertical&horizontal direction.In general,the evolution and distribution of sedimentary facies are influenced by ancient landform,ancient tectonic events and sea-level's change.In the study of reservoirs,the main types of reservoir rocks are grain dolostone,and dolomitized limestone which could see the palaeobios' remains and different types of pore include intracrystalline pore,intergranular dissolved pore.And in general case,these 2 kind of rocks are derived from grain limestone after it modified by dolomization.In the research area,platform edge subfacies with high-terrain is easy to be modified by dissolution and dolomization,and then make the grain limestone transformed to grain dolostone,dolomitized limestone which possess high porosity-permeability.But subfacies in the low-terrain like gentle slope and slope—basin,despite grain beach with small-scale on somewhere is relatively higher than gentle slope could be impacted by dissolution and dolomization,they barely have no pore developing in deposition,unless they got affected by tectonic movement and then generated structural fractures.So,it's Sedimentary micro geomorphology controls the development of reservoir.