| Shuaiduomaoshan area is located in the southern part of Qintong Sag in Subei Basin.In the research area,the subvolcanic diabase is developed in Funing Formation,and the eruptive basalt is developed in Sanduo Formation.On June 26,2011,an oil-bearing section 37.5 meters related to volcanic passage was unexpectedly discovered in well Shuai1-7 in Fu-4 section,which brings in the initial understanding that there would be some special reservoirs in Fu-4 section of Shuaiduo oilfield in the volcanic subvolcanic rock zone.Following that,some similar reservoirs were found in well Shuai-4 and well Shuai-5.However,this kind of reservoir is characterized by the large reservoir thickness,small reservoir area and fractured reservoir.Through seismic interpretation technology,several geologic bodies similar to well Shuai 1-7 have been found in Maoshan-Shuaiduo area,which indicates that this type of trap exists universally,and with great exploration potential.In order to further the geological understanding of such reservoirs to expand the exploration achievement and to improve the development effect of the sub-volcanic reservoirs,it becomes urgent to conduct systematic and pertinent study on the genesis of this new type of reservoirs.Therefore,starting from the study of volcanic mechanism,this paper aims to find out the genesis and development law of this kind of reservoir.In this study,multiple analytical means including core logging,X-ray diffraction analysis,thin section analysis,scanning electron microscopy,physical analysis,casting thin section,mercury injection analysis,isotope dating,seismic interpretation and inversion,logging interpretation are applied by starting from macro and combining with micro-analysis ideas to find out the characteristics and distribution of Sanduo formation basalt,the characteristics and distribution of Funing formation diabase,and those of the subvolcanoes.Based on the analysis of the characteristics and genesis of the related rocks,the volcanic mechanism model was established after understanding the relationship among the three lithological types,with the lithologic types and genesis of the developed reservoirs being identified,and the development and distribution of the new types of reservoirs being predicted.Through the above-mentioned analysis,the following understanding and achievements have been realized:1)Ejective basalts are mainly developed in Duo'er Member which erupted from several volcanic craters.The subvolcanic rocks are mainly developed in Funing Formation,that are inconsistent with bedding or micro-angle intrusion,which are mainly the diabase,with the transition to basalt in shallow strata.2)Isotope dating results show that the eruptive basalts of Duo'er Member and the diabase of Funing Formation are the products of magmatic activity of the same period with similar age and chemical composition.3)The thick reservoirs penetrated in wells Shuai 1-7,Shuai 5 and Shuai 4 are the cryptoexplosive breccia reservoirs.It is believed that the cryptoexplosive breccia is formed by the comprehensive action of sub-volcanic rocks,with the formation fluids in the third member of Fu-4 Formation in the relative uplift area of mudstone at the fourth member of Fu-4 Formation where the caprock is in the depth of about 1000 meters.4)The cryptoexplosive breccia is generally developed in the mudstone of the fourth member of Fu-4 section,which has the characteristics of small plane range and large longitudinal thickness and is able to form traps by itself and reservoir under the pumping action of subvolcanic rock mass.Therefore,it is the most advantageous exploration target under the volcanic mechanism in the study area.Comprehensive analysis shows that there are 7 such targets developed in the study area. |
PDF Full Text Request