107 / 2022-02-17 09:15:12

New discovery of sandy clastic flow sand body and its significance of oil and gas exploration in Junggar basin, NW China

Junggar basin；Western Well Pen-1 sag；Sangonghe formation；sandy debris flow；lithologic trap；Oil and gas exploration

Jurassic which shallower buried was the most important field to find high-efficiency oil and gas reservoirs in the hinterland of Junggar basin. After the breakthrough of lithologic reservoir exploration of well SN31 in 2004, a number of exploration wells were deployed according to the lithologic trap pattern of well SN31, all of which were declared to be unsuccessful¹. At present, there had been no major breakthrough in the exploration of oil and gas in the abdomen in the past 15 years. The key problem restricting the breakthrough in the exploration of oil and gas was that the lateral shielding conditions of sand bodies are not implemented, and the lithologic traps were not implemented. According to the current situation of oil and gas exploration in the abdomen, the exploration degree of low convex zone was higher than that of depression area. Were effective sand bodies developed in the depression? Does the sand body had lateral shielding conditions? Was lithologic trap implemented? These key problems restricted the next step of exploration. Therefore, it was urgent to reorganize the genetic types and lithologic trap conditions of the sand bodies in the southern depression, established a new lithologic trap model, and found a new replacement field. On the basis of fully absorbing the previous research results, through core observation, heavy mineral analysis, reservoir characterization and seismic reflection characteristics analysis, the paleogeomorphology, sedimentary microfacies, reservoir properties and oil-gas properties of the second member of Sangonghe Formation in the western Pen-1 depression were analyzed, and the typical sandy clastic flow sand bodies, top, bottom and side, were proposed The directional blocking condition was better, and the lithologic trap condition was superior. The results showed that the second member of Sangonghe formation around the western Pen-1 depression develops multi-stage ring-shaped slope break, the sand body of delta front was developed above the slope break, and under the trigger of Yanshanian tectonic activity, the sand clastic flow sand body was formed under the slope break. Compared with other basins at home and abroad, the identification mark of sandy clastic flow sand body retained the reservoir physical properties and oil-gas properties of the front facies sand body, which was the most favorable exploration field for the next oil-gas exploration. This recognition had been applied to the well location deployment of oil field and achieved good application results. According to this understanding, well QS2 was deployed for the sandy clastic flow sand body under the slope break in the oilfield, and a major breakthrough was made after drilling. The breakthrough of well QS2 broke the deadlock of exploration for lithologic reservoir in the abdomen, opened up a new scene of exploration for large-scale lithologic reservoir in the depression, and confirmed that the sandy clastic flow sand body under the slope break had the conditions for forming large-scale lithologic reservoir.