新疆北部石炭系火山岩风化壳有效储层特征及分布规律

Characters and distribution patterns of effective reservoirs in the Carboniferous volcanic weathering crust in northern Xinjiang

利用露头、岩心、测井、地震、分析化验等资料对新疆北部石炭系火山岩风化壳进行了综合研究,建立了利用风化指数识别风化壳结构的模型。火山岩风化壳具有土壤层、水解带、溶蚀带、崩解带和母岩5层结构,其中溶蚀带、崩解带储层物性最好。火山岩风化壳储层孔隙喉道半径分布概率呈现出双峰特征;储集空间类型主要包括溶蚀孔隙型、孔隙-裂缝型、裂缝型和洞缝型4类,其中溶蚀孔隙是其主要储集空间,裂缝是其主要的渗流空间。在断裂不发育处火山岩风化壳有效储层厚度可达510m,在断裂发育处有效储层可深至风化面之下1 100m。火山岩风化壳储层主要分布于古地貌高部位、斜坡带和低部位的断裂发育处,其形成受控于古地貌、断裂和风化淋滤时间。

Volcanic weathering crust has been considered as a kind of significant reservoirs,its genetic conditions,characteristics,types and distribution patterns currently become an advanced research topic of reservoirs.Through comprehensive research of volcanic outcrops,cores,logs,seismic and laboratory analyses of the Carboniferous in northern Xinjiang,a five-layer structural complex of volcanic weathering crust was proposed,namely soil layer,hydrolysis belt,corrosion belt,disintegration belt and parent rock.A weathering index model to identify weathering crust structures was then built.Reservoir properties of the corrosion and disintegration belts were recognized to be the best of the five-layer structures.Pore throat radius probability of the volcanic weathering crust showed a bimodal distribution.Chiefly,4 types of reservoir space,including corroded pore,pore-fracture,fracture and cavity,were identified,of which corroded pores dominated the reservoir space and fractures controlled the main seepage space.In the whole volcanic weathering crust,the thickness of effective reservoir rocks in fault-undeveloped places could reach to 510m,while that in fault-developed places stretched downward to 1100m.The formation of five-layer structures of reservoir rocks was controlled by paleogeomorphology,fault,weathering and leaching time.These rocks were mainly distributed in high parts of paleogeomorphology,slope belts and low-lying parts of fault-developed places.These conclusions have not only enriched the volcanic reservoir theory,but also instructed the exploration and well depth design,which have expanded exploration targets of the Kelameili Oilfield and Niudong Oilfield.Meanwhile,the theory is of great scientific significance and application in focusing oil and gas exploration on volcanic weathered crust.