琼东南盆地长昌凹陷三维地震区中新统微观构造成因探讨
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摘要
基于高精度三维地震资料的精细解释和方差体顺层切片技术,在琼东南盆地长昌凹陷中新统首次发现高密度小断裂,它们近SN走向,断距6～28m,长0.5～4km,倾角约60°。这些小断裂既不是渐新统继承性断裂,也不是近期热点讨论的多边形断层,而是在中新世特定地质条件下由局部引张形成的微观构造。其成因为:1)中新世琼东南盆地处于坳陷阶段,仅控盆断层有微弱活动,长昌凹陷内一般不发育断裂;2)研究区不存在EW向的应力场,无法形成近SN向的微观断裂;3)中新统和渐新统断裂是两套断裂体系,渐新统断裂总体呈NW向,空间分布规律差异较大,主要受控于古近纪构造格局,而中新统小断裂为近SN向,与渐新统断裂无继承性;4)多边形断层往往边数不一,边界形状分布不规则,与中新统规则的SN向小断裂有显著区别。这种高密度小断裂对南海深水油气勘探具有重要意义。
By means of detailed interpretation and variance cube surface slice technology of high frequency 3-dimentional seismic data,a great denseness of microfaults are firstly discovered in Miocene strata in Changchang Depression,Qiongdongnan Basin.They are approximately in SN direction,cut off 6～28m and 0.5～4km long with about 60° obliquity.It is indicated that these microfault systems neither have a consequential relationship with early faults nor polygonal faults that recently discussed on so they were formed by local extension in special geological conditions during Mesozoic period.The genesis of them is summarized in four aspects: 1) During Miocene,Qiongdongnan Basin had entranced postrift stage and Changchang Depression developed with no faults except for basin-controlled faults.2) SN-directional microfaults would not develop in the depression because there is not EW-directional stress in this region.3) The Oligocene faults and Miocene faults are two sets of fault systems because the Oligocene faults are in NW direction and have great difference in spatial distribution,which are dominantly controlled by Paleocene structural patterns that,while the Miocene microfaults are in SN direction and have no relationship with the Oligocene fault system.4) Polygonal faults are commonly with diverse boundary numbers and anomalistic boundary shapes,which are greatly different with Miocene SN-directional faults.It is believed that the existence of these high dense microfaults is most significant to oil and gas exploration in deep water.
By means of detailed interpretation and variance cube surface slice technology of high frequency 3-dimentional seismic data,a great denseness of microfaults are firstly discovered in Miocene strata in Changchang Depression,Qiongdongnan Basin.They are approximately in SN direction,cut off 6～28m and 0.5～4km long with about 60° obliquity.It is indicated that these microfault systems neither have a consequential relationship with early faults nor polygonal faults that recently discussed on so they were formed by local extension in special geological conditions during Mesozoic period.The genesis of them is summarized in four aspects: 1) During Miocene,Qiongdongnan Basin had entranced postrift stage and Changchang Depression developed with no faults except for basin-controlled faults.2) SN-directional microfaults would not develop in the depression because there is not EW-directional stress in this region.3) The Oligocene faults and Miocene faults are two sets of fault systems because the Oligocene faults are in NW direction and have great difference in spatial distribution,which are dominantly controlled by Paleocene structural patterns that,while the Miocene microfaults are in SN direction and have no relationship with the Oligocene fault system.4) Polygonal faults are commonly with diverse boundary numbers and anomalistic boundary shapes,which are greatly different with Miocene SN-directional faults.It is believed that the existence of these high dense microfaults is most significant to oil and gas exploration in deep water.
引文
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[7]Hustoft S,Mienert J,Bünz S,et a1.High resolution 3D-seismicdata indicate focused fluid migration pathways above polygonalfault systems of the mid-Norwegian margin[J].Marine Geology,2007,245(1/4):89-106.
[8]Bull S,Cartwright J,Huuse M.A subsurface evacuation model forsubmarine slope failure[J].Basin Research,2009,21:433-443.
[9]Lonergan L,Cartwright J,Jolly R.The geometry of polygonal faultsystems in Tertiary mud rocks of the North Sea[J].Journal ofStructural Geology,1998,20(5):529-548.
[2]吴时国,孙启良,吴拓宇,等.琼东南盆地深水区多边形断层的发现及其油气意义[J].石油学报,2009,30(1):22-26.
[3]李绪宣,钟志洪,董伟良.琼东南盆地古近纪裂陷构造特征及其动力学机制[J].石油勘探与开发,2006,33(6):713-721.
[4]于俊峰,段如泰.琼东南盆地2号断裂东带发育特征及形成机理[J].大地构造与成矿学,2008,32(3):293-299.
[5]周心怀,余一欣,汤良杰,等.渤海地区底辟构造及其油气地质意义[J].石油学报,2009,30(4):518-521.
[6]Gay A,Lopez M,Cochonat P,et a1.Evidences of early to latefluid migration from an upper Miocene turbiditic channel re-vealed by 3D seismic coupled to geochemical sampling with-in sea floor pock marks,Lower Congo Basin[J].Marine andPetroleum Geology,2006,23(3):387-399.
[7]Hustoft S,Mienert J,Bünz S,et a1.High resolution 3D-seismicdata indicate focused fluid migration pathways above polygonalfault systems of the mid-Norwegian margin[J].Marine Geology,2007,245(1/4):89-106.
[8]Bull S,Cartwright J,Huuse M.A subsurface evacuation model forsubmarine slope failure[J].Basin Research,2009,21:433-443.
[9]Lonergan L,Cartwright J,Jolly R.The geometry of polygonal faultsystems in Tertiary mud rocks of the North Sea[J].Journal ofStructural Geology,1998,20(5):529-548.
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