Sedimentary Architecture and Sand Body Configuration of the Large Braided River Delta in Shallow Lacustrine Basin: A Case Study From Bashijiqike Formation of Cretaceous in the Kuqa Depression of Tarim Basin, Northwest China

Abstract

Large braided river delta was developed in shallow lacustrine, which is important oil and gas exploration field, tectonic and sedimentary evolution in kuqa depression of tarim basin experienced three stages, strong structural extrusion stage between 134-126Ma(yageliemu formation), stress release and rapid subsidence stage between 126-109Ma(shushanhe-baxigai formation), slow subsidence stage and formed shallow sedimentary basin between 109-92Ma(bashijiqike formation). Five large shallow braided river delta were developed between 109-92Ma and their distribution area was about 2000 square kilometers. And the trillions of cubic natural gas reserves were proved. Its thought that sedimentary architecture and sand body configuration is the key to oil and gas exploration and development. By mean of research of outcrop, seismic, logging and experimental data, the characteristics of the braided river deltaic development and stratigraghic architecture were revealed that dry ancient climate period, a lot of shallow water sedimentary mark (mud crack, abundant shallow water trace fossil assemblages), more than the thickness of 350 meters, the lithology of fine sandstone, siltstone and small amount of mudstone, with high sandstone proportion (80-90%). Five kind patterns of sand body construction in vertical were recognized and 80% of that was box-logging type of branch channel sandstone. The thickness of mudstone layer was only 0.5-1 meters, with 50-100 meters extended distance. The conclusions can be drawn that the large braided river delta was developed on the background of shallow lacustrine with big sedimentary thickness and higher sand ratio. The dominant of sand body was the branch channel, which accreted vertically to compound sand body, with large area distribution. The mudstone had thin thickness and short extended distance. And therefore, looking for the large anticline reservoir of branch channel sandstone is the key factor to increase reserves and production.

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018