| Author's Name: WANG Bo, WANG Yanqing, MA Jinye, GONG Qingshun, ZHU Jun,
ZHU Chao, LI Yanan, WANG Yuanfei, PEI Ziwei, ZHANG Jun, WEI Wei |
| The exploration of the Jurassic oil and gas system in the Qaidam Basin has led to the discovery of Dongping,
Niudong, and Kunteyi bedrock gas fields, as well as Niudong and Lenghu Jurassic oil fields. Currently, there is an urgent
need to expand the exploration field of the Jurassic and search for replacement zones. The sedimentary characteristics and
reservoir formation conditions of the Middle Jurassic in Jiulongshan area are analyzed by using drilling cores, logging,
seismic, and experimental data. The results indicate that: (1) The Middle Jurassic in Jiulongshan area developed continental
coal bearing sedimentary formations in a humid climate, belonging to the wetland braided river delta deposits. (2) Three
types of lithofacies associations are developed in the Middle Jurassic. The first is interbedding of light grey and brown
grey mudstone and sandstone, pebbly sandstone, glutenite and conglomerate; the second is interbedding of coal seam, dark
grey carbonaceous mudstone and sandstone, pebbly sandstone and conglomerate; and the third is interbedding of dark grey
carbonaceous mudstone, oil shale and mudstone. The three types of lithofacies associations correspond to the upper plain,
lower plain to front, and lacustrine deposits of the braided river delta, respectively. (3) The distribution of Middle Jurassic
sand bodies are characterized by multiple overlapping periods, rapid lateral changes, and frequent migration of river
channels that result in braided, network, and flower shaped features on the plane. It is suggested that the channel sand
bodies of lower plain and front in the braided river delta of the Middle Jurassic have excellent oil and gas accumulation
conditions, which are important areas for conventional oil and gas exploration in the Jiulongshan area. The lacustrine oil
shale is a potential area for unconventional oil exploration in this area. |
