| PDF: | |
| Time: | 2017 |
| Journal: | Jilin University |
| Pages: | |
| Type: | Thesis |
| Author: | Xiang Gao |
Abstract: | Well called SK2 is the deepest scientific well in China. And the well which drills the stratum of continental non-marine Cretaceous also be the first borehole supported by ICDP in the world. SK2 will drill complete Cretaceous stratum and collect lower Cretaceous stratum including Huoshiling formation, Shahezi formation and Yingcheng formation. Up to now, the depth of well is 5922m, and the recovery is 95.4%. The article according to SK2 lithology of core and cutting , drawing subsidence curve of SK2 by stripping inversion method after handing data by programme. And study the core of Yingcheng formation. Main conclusions are as follows: (1)SK2 project has collected 365.32m of the lower Cretaceous Yingcheng Formation which corresponds to Aptian-Albian. The borehole got a highly continuous core section with recovery of 98.47%。. The diameter of core is 214mm which is among the largest diameter concerning coring engineering. Considering the sedimentary and volcanic rocks as a whole sequence, we mainly recognized seventeen rock types from drilling core of the Yingcheng Formation. There are nine types of sedimentary rocks, which include conglomerate, coarse sandstone, medium sandstone, fine sandstone, siltstone, silty mudstone, mudstone, breccia tuffaceous sandstone, breccia-bearing tuffaceous sandstone. There are eight types of volcanic rocks including rhyolite, rhyolitic tuff/pyroclastics/agglomerate, rhyolitic welded tuff, crypto-explosive breccia, andesitic tuff, and tuffite. (2)Sedimentary facies is fan delta dominant which includes five sedimentary microfacies of distributary channels, back swamp between delta, subaqueous distributary channels, subaqueous mouth bar and mudstone of still water. Volcanic facies are explosive facies and effusive facies dominant, which include four volcanic subfacies of air-fall, pyroclastic flow deposits, middle and upper flow subfacies of the effusive one. (3)According to detail description of the Yingcheng sequence, we first recognized three periodic sedimentary and volcanic cycles in the Yingcheng Formation, which have been numbered sedimentary I - volcanic I, sedimentary II - volcanic II, and sedimentary III – volcanic III. This is a new discovery concerning the vertical features of of the Yingcheng Formation. We also find the thickness of explosive facies increase but effusive facies decrease from deep to shallow in volcanic II. (4)The main characteristic of subsidence curve of SK2 is gently in volcanic period while steeply in sedimentary period. It includes three stage : Huoshiling formation gently – Shahezi formation steeply, Yingcheng formation gently – Denglouku and Quantou formation steeply, Qingshankou formation gently – Yaojia and Nenjiang formation steeply. The latter two stages which have faster subsidence speed in post-rift while the first stage in syn-rift seems slowly. After the three stages is Sifangtai formation – Mingshui formation – now stage which more straightness even upward. The abrove four stages express the subsidence speed of Songliao basin and decide how thickness the sediment could be. The centimeter scale description on the core sections from the SK2 may provide some other useful information for related researches in the future. |