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The Sedimentary Facies And Diagenesis Of Tight Sandstone Reservoirs Of Huagang Formation In West Subdepression Of Xihu Depression, East China Sea

Posted on:2013-04-12Degree:MasterType:Thesis
Country:ChinaCandidate:Z X XuFull Text:PDF
GTID:2180330467452929Subject:Geological engineering
Abstract/Summary:PDF Full Text Request
Based on the theories and technologies of terrigenous clastic sedimentology, reservoir geology and mineral rock combined with the core data, logging curves, conventional thin sections, and casting thin sections, the sedimentary facies characteristics, the types of diagenesis, the porosity evolution, and the influencing factors on the qualities of the sandstone reservoirs of Huagang Formation in West Subdepression of Xihu Depression are comprehensively studied. In addition, the distribution laws of the relatively high-quality reservoirs are also discussed.It is demonstrated that the reservoir in Huagang formation is impacted by three different sedimentary facies-(rivers-delta-lake facies) during different deposition periods of the Xihu Depression which is defined as the continental lake-delta depositional system. the lower section of Huagang Formation deposited in the early Oligocene, which is mainly delta plain and distributed in the western edge of the basin with the delta deposition constantly advancing to the basin constituting the prograded delta. The sandbodies of the lower section of Huagang Formation are mainly composed of the side-beach sand of the delta plain, meandering river and channel sand of plain distributary. The sedimentary facies of the upper section in Huagang Formation are mainly shore-shallow lacustrine and leading edge of delta which consisted several microfacies such as the estuarine sand bar, the subaqueous distributary channel, the underwater tributary bay and the sand sheet with high clay content in the form of sand and mud interlayer. The sediment sources of the Huagang Formation are mainly from two directions_one from the western slope zone and the other form the central uplift zone.Diagenesis especially the compaction followed by precipitation and dissolution has has significantly influenced the reservoir qulity of Huagang Formation. Compaction is one of destructive diagenesis. under the microscope, It is found that the contact relationships of the debris particles in the core thin sections from Well2, and Well1are Line-bump contact or suture line contact, showing that the sandstone reservoirs have experienced a strong compaction. Controlled by the depositional environment, the reservoir of the Huanggang formation has a high clay content relatively strengthening of the reservoir compaction strength whose devastating effects to the reservoir quality are serious. Since the cements plug the pore throats and the chlorite cement and the siliceous cement increase the resistance pressure capability of pore throat, the influence of the precipitation on the reservoir is neutral. Although the chlorite and siliceous cement in Huagang Formation is rare, the have played a significant roles in the improvement of reservoirs.Dissolution in the Huagang reservoirs is more developed whose contribution ratio to the reservoirs is up to reach50%or even higher.Combined with the formers’view points and the results of this study, it is found that the relatively high-quality reservoir of Huagang Formation is near the junction of upper section and the lower section, after analyzing the information such as loging and core, it is believed that the high-quality reservoirs are located near the conversion point of base-level decline-half-cycle and rise-half-cycle. At this point, the role of sand body accommodates each other and have reached the maximum accommodation, which is easier to form sandstone reservoirs with high porosity and permeability. Statistics shows that the types of relatively high-quality reservoirs are underwater distributary channel sand and estuarine sand bar. In addition, it is easy to form a relatively high-quality reservoir; when the dissolution is developed.Through the studies of the reservoir rock diagenesis, the physical properties and the pore structure, two relatively high-quality reservoir intervals(H5and H9+10) are identified in Well1. One relatively high-quality reservoir interval(H7) is also identified in Well2. In Well3, two relatively high-quality reservoir intervals(H11and H12) are identified.
Keywords/Search Tags:Xihu Depression, Huagang Formation, sedimentary facies, diagenesis, the relatively high-quality reservoirs
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