Genesis and Characteristics of the Lower Triassic tight reservoirs, West Slope of Mahu area, Junggar Basin

Yin, Lu; Wang, Guodong; Chen, Yongbo; Wang, Bin; Xu, Duonian; Bai, Xiaoyin; Huang, Yu; Chen, Xuzhen

High quality and efficient reserves decrease with the development of oil and gas exploration, and the hydrocarbon accumulation in the tight reservoirs gradually becomes hot. This kind of low abundance and widespread unconventional reserves have been found in the Yanchang Formation of the Erdos Basin and the Xujiahe Formation of the Sichuan Basin in China. The study of tight sandstone reservoirs is the key to the oil-gas exploration and development of unconventional reserves in Erdos and Sichuan Basin.

Recently, massive hydrocarbon accumulation in tight sandstone is also found in the Baikouquan Formation of the Lower Triassic, west slope of Mahu area, Junggar Basin. The sandstones represent typical characters of tight reservoir, with gray and greyish-green glutenite of front fan delta facies, low compositional and structural maturity, porosity of 5%-10%, average porosity of 7.8%, permeability of 0.01-204MD, average permeability of 0.84MD, and pore throat concentrated below 0.5μm. We discuss the genetic mechanism of tight reservoir and distribution of high quality reservoirs in the Lower Triassic, west slope of Muhu area, using the data of pore, casting lamella, SEM and X-ray diffraction.

Through the study of rock and minerals, sedimentary environment and microelement, we divide the reservoirs into seven diagenetic facies, define the genetic mechanism of tight reservoirs and corroded pores, and propose that the four factors of provenance, facies belts and zones of secondary pore and fracture jointly control the distribution of high quality reservoirs. According to this, we believe that the lower depth limit of oil-gas exploration in non-fractured areas is 4500m and 5500m in fractured zones, which is different to the previous view of the lower depth of 3500m. This study has reference value to predict favorable reservoirs and guide the oil-gas exploration in tight-sandstone area.

Key words: west slope of Muhu area; Baikouquan Formation; tight reservoir; glutenite

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013