岩浆岩与变质岩风化壳储集层差异--以阿尔金山山前带东段基岩储集层为例

Differences Between Weathering Crust Reservoirs in Magmatic Rocks and Metamorphic Rocks:A Case Study of Bedrock Reservoirs in the Eastern Segment of Altun Piedmont Area

阿尔金山山前带东段基岩风化壳储集层以岩浆岩风化壳和变质岩风化壳为主,为了解2种风化壳储集层的差异,通过岩心观察描述,借助常规测井曲线和地层微电阻率扫描成像测井图像识别基岩风化壳结构,对典型井风化壳结构进行划分,绘制连井剖面;通过岩心观察、薄片鉴定、扫描电镜、元素能谱测井、常规测井、常量元素测试、氦孔隙度-空气渗透率测试数据等总结2种风化壳储集层在矿物成分、地球化学响应、常规测井、储集空间特征方面的差异,建立岩浆岩和变质岩风化壳储集层发育模式。结果表明,基岩风化壳按风化程度由上至下划分为土壤层、完全风化层、半风化层和未风化层4层结构,为了便于研究又将半风化层细分为半风化层溶蚀带和半风化层崩解带。岩浆岩矿物纵向分布形式差异不大;变质岩由浅到深暗色矿物和黏土矿物含量整体减少。通过SiO2/Al2O3可知,研究区基岩多处于半风化状态,花岗岩SiO2/Al2O3为5.13~6.50,较稳定;变质岩SiO2/Al2O3为3.01~6.53,变化较大。岩浆岩半风化层溶蚀带储集空间类型为裂缝-孔洞型,半风化层崩解带储集空间类型为裂缝型;变质岩半风化层溶蚀带储集空间类型为孔洞型,半风化层崩解带储集空间为孔洞-裂缝型。变质岩半风化层溶蚀带孔隙度为0.413%~8.509%,岩浆岩半风化层溶蚀带孔隙度为0.926%~7.152%;变质岩半风化层崩解带孔隙度为1.367%~5.211%,岩浆岩半风化层崩解带孔隙度为1.429%~8.572%.岩浆岩和变质岩半风化层崩解带孔隙度和渗透率之间的相关性较半风化层溶蚀带好。变质岩半风化层溶蚀带是变质岩风化壳储集层最重要的储集层,是稳产的主要因素,其次是半风化层崩解带;岩浆岩半风化层崩解带是岩浆岩风化壳储集层最重要的储集层,其次是半风化层溶蚀带。变质岩风化壳储集层的储集性能优于岩浆岩岩风化壳储集层。

The bedrock weathering crust reservoirs in the eastern segment of the Altun piedmont area are dominated by magmatic weather ing crust and metamorphic weathering crust.In order to understand the differences between the two kinds of weathering crust reservoirs,the weathering crust structures of the bedrock are identified through core observation,conventional logging curves and FMI image logging.The weathering crust structures in typical wells are classified and well tie sections are mapped.Based on core observation,thin section identifi cation,scanning electron microscopy,elemental energy spectrum logging,conventional logging,constant element testing and helium porosi ty air permeability testing data,the differences in mineral composition,geochemical response,conventional logging,reservoir spaces and characteristics between the two kinds of weathering crust reservoirs are summarized,and the development model of weathering crust reser voirs of magmatic and metamorphic rocks are established.The results show that the weathering crust of bedrock can be divided into four layers according to its weathering degree,namely soil layer,full weathered layer,semi weathered layer and unweathered layer,and the semi weather layer is further divided into dissolved zone and disintegrated zone.There is little difference in the vertical distribution of magmatic minerals.The contents of mafic minerals and clay in the metamorphic rocks from shallow to deep decrease as a whole.It can be discovered from SiO2/Al2O3 that the bedrock in the study area is mostly in semi weathering state,the SiO2/Al2O3 of granite ranges from 5.13 to 6.50 and that of the metamorphic rock is 3.01-6.53.In the magmatic rock,the reservoir space of the dissolved zone in the semi weathered layer is fractured vuggy type,and the reservoir space of the disintegrated zone in the semi weathered layer is fractured type;in the metamorphic rock,the reservoir space of dissolution zone in the semi weathered layer belongs to vuggy type,and that of the disintegrated zone of semi weathered layer is vuggy fractured type.The porosities of the dissolved zones of the semi weathered layer in the metamorphic rock and mag matic rock are 0.413%-8.509%and 0.926%-7.152%,respectively;the porosities of the disintegrated zones of the semi weathered layers in the metamorphic rock and magmatic rock are 1.367%-5.211%and 1.429%-8.572%,respectively.In the magmatic rock and metamorphic rock,the correlation between porosity and permeability of the disintegrated zones in the semi weathered layers are better than that of the dissolved zones in the semi weathered layers.The dissolved zone of the semi weathered layer in the metamorphic rock is the most important reservoir of the weathered crust,and is also the key factor for stable oil production,followed by the disintegrated zone of the semi weathered layer.The disintegrated zone of the semi weathered layer is the most important reservoir of weathered crust reservoir in the magmatic rock,followed by the dissolved zone of the semi weathered layer.The reservoir performance of the metamorphic weathering crust reservoir is bet ter than that of magmatic weathering crust reservoir.