Genesis and pore development characteristics of Permian Lucaogou migmatites, Jimsar Sag, Junggar Basin

Abstract

Taking the influence of lithological characteristics differences on the genesis of pores in migmatite reservoirs as the main line, the genesis and characteristics of pores were analyzed from the perspective of the relationship between rock fabric and grain deposition. (1) Based on hydrodynamic conditions, mineral assemblage and rock structure characteristics, and taking three endmembers of clastic particles, clay minerals and carbonate minerals for classification, the "sweet spots" in the Lucaogou Formation are mainly composed of tuffaceous sandy dolomite, tuffaceous feldspar detrital siltstone, tuffaceous dolomitic sandstone and tuffaceous dolomitic siltstone. The migmatites have mixed sources, and various types of migmatite layers can be superimposed on each other vertically to form facies marginal mixing. (2) Based on the spherical accumulation model, when the content of debris particles is lower than 52.4%, the porosity decreases with the increase of particle content. When the content of clastic particles reaches 52.4%, if the content of clastic particles[JP]continues to increase, large number of ntergranular pores will appear, and the porosity will increase rapidly, gradually evolving into a conventional sandstone reservoir. (3) According to the relationship between the three end components of clastic particles, clay minerals and carbonate minerals and the pore types, the pores of the migmatites in the Lucaogou Formation can be classified into three types including intergranular pore, intragranular dissolved pore and intercrystalline pore. The pores in tuffaceous sandy dolomites and tuffaceous feldspar detrital siltstones are mainly intergranular and intragranular dissolved ones supported by particles, while those in tuffaceous dolomitic sandstones and tuffaceous dolomitic siltstones are mainly intercrystalline ones. The development of high-quality migmatite reservoirs is mainly controlled by the content of clastic particle components, and the content of soluble clastic components and dissolution effect can improve the physical properties of the reservoirs.

Keywords

• migmatite
• genesis of migmatite
• pore characteristics
• lucaogou formation
• jimsar sag
• junggar basin