Characteristics Of Clay Minerals In Alkali Lakes And Their Influence On Hydrocarbon Generation Evolution Of Source Rocks

Alkali lake sedimentary basin is the main place of oil shale development in the world,which is of great significance to oil and gas exploration.Clay minerals are important components of sedimentary rocks,and their types and contents can indicate the degree of diagenesis and evolution,and are closely related to the process of oil and gas generation.Although the relationship between clay minerals and source rocks has attracted wide attention of scholars,there is little research on the composition characteristics of clay minerals in alkali lakes at present,and its role in hydrocarbon generation remains to be answered.Therefore,in this paper,the source rocks of Fengcheng Formation are selected as representative samples and relevant artificial samples are prepared,and the gold tube thermal simulation experiment is carried out to analyze the clay mineral composition characteristics of several typical alkali lake source rocks represented by Fengcheng Formation,and to study the influence of clay mineral transformation in alkali lake on hydrocarbon generation and evolution.The results show that the clay minerals in the source rocks of Fengcheng Formation are characterized by relatively high content of illite and low content of illite.Based on the analysis of several sedimentary basins such as Hetaoyuan Formation in Biyang Depression,it is found that the clay minerals in alkali lake sedimentary basin generally show the slow illitization of montmorillonite.Combined with the sedimentary background of alkali lake,it is speculated that the abnormal transformation of montmorillonite is mainly influenced by volcanic rocks,climate and diagenetic fluid in the source area.The basic volcanic rocks and the paleoclimate of alternating wet and dry promoted the formation of montmorillonite,while the alkaline water with CO₃^2-as the main anion inhibited the illitization of montmorillonite.The analysis results of clay minerals in the thermal simulation products indicate that the montmorillonite transformation is indeed inhibited in the solution environment with CO₃^2-as the main anion.Further analysis of the generated organic matter indicates that the high content of montmorillonite in the alkali lake can protect the organic matter,thus inhibiting the hydrocarbon generation and cracking of the organic matter.The relatively high montmorillonite content in the alkaline sedimentary basin extends the hydrocarbon generation period of the source rocks to a certain extent,which makes it possible for secondary hydrocarbon generation.