Development Model and Distribution Characteristics of Continental Dolomitic Reservoir in Western Junggar Basin

The genesis of dolomites is a research topic attracting great attention in sedimentology. Previous studies mainly focused on the causes of marine dolomite, and made a variety of genetic patterns. However, much less studies have been conducted for genesis of continental dolomite in lacustrine basins, which was found in some sags of China including Shahejie Formation of Paleogene in Dongying sag, Hetaoyuan Formation of Paleogene System in Miyang sag, and Lucaogou Formation of Middle Permian in Santanghu Basin, where discoveries have been gained in these dolomite, and without exception, good results in the explorations. Therefore, the genesis mechanism and distribution laws of continental dolomite in lacustrine basins have aroused the interests for both the foreign and domestic scholars gradually.

In recent years, continental dolomite of lacustrine basins has been found in Permian Fengcheng Formation of, western Junggar Basin, with a dolomite content of 15% -80%( average 24%), where most of dolomite do not meet the component targets for the nomenclature. Thereby, it was greatly different from the typical dolomite in components and genesis mechanism. In this paper, thin section, trace elements and stable isotope were used to study genesis mechanism and distribution characters of the continental dolomitic reservoir in Western Junggar Basin.

Through mineral characteristics, paleontological and geochemical features, studies suggested that the dolomite of Fengcheng Formation was formed in a high salinity, high magnesium to calcium ratio and strong reducing sedimentary environment. According to the analysis of the sources of magnesium in the dolomite of Fengcheng Formation, it can be concluded that lamellar-dolomite was developed during the parasyngenetic period, while scattered-dolomite was formed during burial period by eluviation and metasomatism of volcanic materials; While the magnesium in dolomite of Xiazijie Formation was from the deep hydrotherm by replacing Ca+ in the early carbonate cement of Mg+ in deep hydrothermal according to metasomatism. Combined with study on geological genesis, two geological patterns for continental dolomite in lacustrine basins have been established, effective forecast for the distribution of dolomite has been conducted by using the geophysical methods.  

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California