火山岩风化壳及油气地质意义——以新疆北部石炭系火山岩风化壳为例

Weathered volcanic crust and its petroleum geologic significance:A case study of the Carboniferous volcanic crust in northern Xinjiang

以新疆北部石炭系火山岩风化壳为例,利用露头、岩心、试油和测井等资料,研究火山岩风化壳特征、分布及油气地质意义。完整火山岩风化壳具有6层结构,即土壤层、水解带、淋蚀带、崩解Ⅰ带、崩解Ⅱ带和母岩,不同结构层具有不同特征和识别标志,有利储集层主要发育于淋蚀带和崩解Ⅰ带内。风化淋蚀时间控制风化壳厚度,火山岩风化壳最大厚度可达550 m,形成时间约46.3 Ma;岩性、岩相、风化程度控制风化壳储集层物性;断裂控制风化壳储集层渗流能力,越靠近断裂渗流半径和渗流能力越大。火山岩风化壳主要分布于古地貌高部位、斜坡带及断裂发育的低洼部位;靠近断裂区油层垂向跨度大。建立火山岩风化程度和有效储集层评价方法和模型,可利用测井资料评价未取心井钻遇的火山岩风化壳风化程度及有效储集层。

The Carboniferous volcanic crust in northern Xinjiang was analyzed as an example to study the characteristics and distribution of volcanic crust and its petroleum significance using the analysis of outcrops, core samples, oil testing, and logging data, etc. A complete weathered volcanic crust has a six-layer structure, which includes soil layer, hydrolysis zone, leached zone, broken-down zone I, broken-down zone I[, and underlying bedrock. The characteristics and indicators for the crust of different layers are different. Effective reservoirs are developed within the leached zone and broken-down zone I. Weathered thickness is controlled by leaching time. The maximum thickness of weathered volcanic crust is about 550 m corresponding to the leaching time of 46.3 Ma. The physical properties of weathered volcanic crust are controlled by litho-facies and weathered intensity. Faults and fractures are the main controlling factors of the percolation ability of weathered volcanic reservoirs. The closer the reservoir is to the fault zone, the better the percolation ability would be. The crust is mainly distributed at the paleo-topographic high place, slopes and low place with developed faults. The vertical span of reservoirs is bigger near the fault zones. According to the established evaluation method and model of weathered volcanic intensity and effective reservoirs, the weathered volcanic intensity and effective reservoirs of none-coring wells can be evaluated.