Paleocave geological modeling in the Ordovician outcrops, Northwest Tarim Basin
Shi Shuyuan1, Liu Wei1, Huang Qingyu1, Qiao Hui2, Zhang Yanqiu3, Li Bohua1
1 Research Institute of Petroleum Exploration and Development, PetroChina, Beijing 100083 2 College of Geosciences, China University of Petroleum(Beijing), Beijing 102249 3 Institute of Petroleum Exploration and Development, Tarim Oilfield Company, PetroChina, Korla 841000, Xinjiang
Abstract：Paleokarst outcrops largely occurred in Northwest Tarim Basin,which provided a good condition for paleocave geological modeling. Combined with outcrop research and Google Earth image,on basis of karst morphology and paleocave architecture characteristics,the large paleocaves could be divided into pipe-hall connected paleocave,single pipe isolated paleocave and streamlined paleocave. There are single paleocave and paleocave group according to their existing forms. Pipe-hall connected paleocave is mainly located in phreatic zone,and its shape contains single lines type,single paleokarst channel type and pipe-hall. The size of hall varies from 50m3 to 50000m3. Single-pipe-isolated paleocave is mainly located in vadose zone,and the shape on section can be circular,ellipse, etc., but the shape on tabular surface is single-streamed pipe. The extending lengths of caves are controlled by the fracture principal orientation. Streamlined paleocave is also located in phreatic zone,distributing along and/or across the strata. Their shape on section is circular,ellipse,lageniform, etc. With the analysis of outcrop structural characteristics,stratigraphic conditions and cave types,we find that pipe-hall connected paleocave is mainly affected by the weathering crust unconformity,and is mainly distributed in Sanjianfang,Wudaoban and Xekar Sections. Single-pipe-isolated paleocave is mainly controlled by unconformity,and distributes in Yijianfang and Liuhuanggou Sections. Streamlined paleocave mainly distributes along both sides of the eroding channel in Xekar Section. Distribution of paleocave group is controlled by various factors. Based on characteristics of large caves and their main controlling factors,a paleocave geological model was proposed. In order to give a guide for forecast of paleokarst reservoir distribution in covering area,the bulk of paleocave group was computed comparing with the volume of “light dot”in North Tarim Basin.
Shi Shuyuan,Liu Wei,Huang Qingyu et al. Paleocave geological modeling in the Ordovician outcrops, Northwest Tarim Basin[J]. JOPC, 2014, 16(6): 802-815.
