基于无人机倾斜摄影的碳酸盐岩生物礁露头多尺度非均质性表征——以鄂西利川见天村露头为例

Characterization of multi-scale heterogeneity of carbonate reef outcrop by UAV oblique photography:Case study of Jiantian Village,Lichuan,western Hubei

针对碳酸盐岩高陡生物礁露头多尺度非均质性研究存在的不足,利用传统野外考察与无人机倾斜摄影数字露头技术相结合,对湖北省西部(鄂西)利川见天村野外多个不同尺度的露头剖面进行了采集、处理与地质解释,基于三维数字露头数据开展了不同尺度的生物礁沉积体系、沉积微相和岩相组合非均质性研究,并对重点露头进行了三维模拟,最后,阐述了生物礁内部有利储层的分布特点。研究表明:(1)无人机倾斜摄影处理后数字模型具有与图像信息对应的三维坐标,可精准定位任意点坐标和测量地质体规模。依据采集信息精度建立了米级别的见天村宏观模型、分米级别的见天村陡崖剖面和厘米级别的采石场剖面等3个模型,为多尺度生物礁非均质性研究奠定了数据基础。(2)露头区大尺度沉积相带主要为自西向东发育的开阔台地、局限台地、生物礁和碳酸盐岩斜坡相。中尺度以生物礁发育礁基、生物丘、礁核和礁顶等4个微相为主,其中,礁基以薄层板状灰岩为主,单层厚约20 cm,总厚60 m;生物丘以多层不规则丘状沉积为特征,单层厚约30 cm,总厚45 m;礁核为不规则的凸起块状岩隆,厚度约为80~120 m;礁顶为块状晶粒白云岩,厚度约为20 m;小尺度礁核内部可以进一步细分为5期旋回,受海平面升降影响,不同旋回生物组合和岩性差异明显。(3)生物礁有利储层以发育晶间孔和晶间溶孔的礁顶晶粒白云岩为最好,其次是发育生物体腔孔和溶蚀孔隙的礁核微相骨架礁灰岩,物性相对较差的为发育黏结格架孔、溶孔和重结晶后的晶间孔礁丘的藻黏结礁灰岩。无人机倾斜摄影技术与传统露头研究方法相结合不仅可以定量表征不同尺度生物礁露头非均质性,而且对指导生物礁型气藏的勘探开发意义重大。

Multi-scale heterogeneity research on the high-steep outcrop area of carbonate rock is very difficult.Outcrop area of multiple scales of Lichuan Jiantian Village data was collected by unmanned aerial vehicle(UAV)oblique photography technology and combined with traditional field outcrop investigation,processing and detailed geological interpretation.The multi-scale reef depositional heterogeneity includes sedimentary system,sedimentary microfacies and lithofacies association.Additionally,the three-dimensional modeling of the significant outcrop was proposed.Finally,the distribution characteristics of high-quality reservoir of the reefs was identified.Research shows that:(1)The data model of the UAV oblique image acquisition processing in the high-steep field outcrop area of the Jiantian Village carbonate rock has three-dimensional coordinates(latitude,longitude,altitude)corresponding to the image information,which can accurately locate any position and measuring the scale of the geological body.Based on the high resolution and accuracy of the collected information,three models were established,including the macro-model of Jiantian Village area at the meter level,the bioherm of Jiantiancun Abrupt Cliff profile at the decimeter level and the Jiantian Village Quarry profile at the centimeter level.(2)The large-scale sedimentary facies in the outcrop area mainly consists of open platform,restricted platform,reef and carbonate slope facies developed from west to east.The reef base,bioherm,reef core and reef cap are the four microfacies developed in the mesoscale reef,among which,the reef base is dominated by thin-platy-limestone with a single layer thickness of about 20 cm and a total thickness of 60 m.Bioherm is characterized by multi-layered irregular sediment with hummocky,with a single layer thickness of about30 cm and a total thickness of 45 m.The reef core is irregular raised massive rock uplift with a thickness of 80-120 m.The reef cap is massive crystal grain dolomite with a thickness of about 20 m.Small scale reef core can be subdivided into five cycles.Affected by base level change,different cycles of biological assemblages and lithology combination are obviously different.(3)Reef top crystal grain dolomite with intercrystalline pores and intercrystalline dissolved pore is the best reservoir,followed by the framework reef limestone with biology coelom pore and dissolution pore of reef core,algae-bonded-reef limestone with growth-framework pore and dissolved pores and recrystallized intercrystal pore of reef mounds.Combination of UAV oblique photography technology and traditional field outcrop investigation can not only quantitatively characterize the multi-scale heterogeneity of reef outcrop,but also has great significance for guiding the exploration and development of reef reservoirs.