Reservoir Characteristics And Controlling Factors Of The Lower Ganchaigou Formation In The Qiquan Oilfield, Qaidam Basin

Based on the investigation of research documents and previous study,sedimentary types and distribution,petrophysical property of the Lower Ganchaigou Formation in Qigequan Oilfield are researched using core samples,logging interpretation,seismic and core test data.The control factors on reservoir quality are also studied.By identifying the marker bed of the lower Ganchaigou Formation in Qigequan Oilfield,this formation is divided into 4 oil zones(???????)in which deposition and petrophysical property are researched respectively.The main lithology of the Lower Ganchaigou Formation is conglomerate,sandy conglomerate,gritstone,sandstone and siltstone.The middle-fine sandstone mainly distributes in the middle-low parts of ? oil zone to middle-upper parts of? oil zone,with the conglomerate and sandy conglomerate developing in the middle-upper parts of ? oil zone and low parts of ? oil zone.The sandy conglomerate and sandstone mainly consist of lithic sandstone and feldspathic lithic sandstone.Combining core analysis and logging interpretation,alluvial fan(fan delta),braided river delta,nearshore subaqueous fan and lacustrine deposit are identified of the Lower Ganchaigou Formation in Qigequan Oilfield.The nearshore subaqueous fan is distributed in the middle and the braided river delta is in the low part and lacustrine deposited in the middle of the Lower Ganchaigou Formation.By comparing the petrophysical property in each oil zone,the ? oil zone has the best property with the average porosity of 16%and average permeability of 19.8×10-3?m2 which is followed by ? oil zone,and ? and ? oil zone are the worst reservoir with the average porosity of 12%and permeability of 14×10-3?m2.Deposition,diagenesis and tectonic movement are the main control factors on reservoir property of the Lower Ganchaigou Formation in Qigequan Oilfield.There are many types of diagenesis which is in the process of early B phase to late A phase.Compaction reduced the porosity greatly,and dissolution had the improvement effect on reservoir property.On the other hand,metasomatism and clay plugged the porosity resulting to the property decline.By analysing regional tectonics,there were multiple tectonic movements which provided plenty of energy and source of sediments.The paleogeographic backgroud with uplift and depression inter distributing contributed to the location of subaqueous fan and fan delta.