Central Junggar Basin, Luliang Gas-water Geochemical Studies

Junggar basin is one of the most important basin with oil and gas in west ,China.The centres of Junggar basin are the most important fields with oil and gas.West-of-well-Pen-No. 1 sag is one of the most important source rock sags of Junggar basin. It has similar geological conditions with neighbouring Mahu sag. Although four oil and gas fields (Shixi, Shinan, Mobei and Luliang) have been discovered around the sag so far, exploration potential is still enormous compared with Mahu sag. Therefore, it is significant for future exploration to study the oil and gas origin and formation timing of the discovered pools.Based on the study of oil and gas origin, source rock maturation and hydrocarbons expulsion history as well as structural development history, oil and gas reservoirs' formation timing is studied. In addition, oil migration and accmulation models are summarized and favourable exploration regions are pointed out.Tncyclic diterpanes C20, C21 and C23 distribution and other geochemical indices show oils around West-of-well-Pen-No. 1 sag have good relationship with those of northwestern margin of the basin, which demonstrated the existence of Permian source-rocks in West-of-well-Pen-No. 1 sag. Oil/source correlation shows Fengcheng formation (Pjf) and Xiawuerhe formation (P2w) are main source beds. Tncyclic diterpanes C20, C21 and C23 distribution also has relationship with oil gravity, oil and gas production, as well as oil pool formation timing and oil source. Rising-patterned oil originates from Fengcheng formation, while peak-patterned oil from Xiawuerhe formation.Four types of migration and accumulation models are put forward: (l)Fault controlled migration and accumulation along ridge far from source region; (2)Fault and unconformity controlled migration and accumulation around source region; (3)Fault controlled migration and accumulation in the slopes within source region; (4)Biogenetic and low temperature catalyzed gas migration and accumulation in middle and shallow formation.Finally, the author points out Luliang uplift, Mobei uplift, Dabasong uplift, slopes of West-of-well-Pen-No. 1 and Mahu sags as well as Maqiao uplift are all favourable exploration regions.