火山岩原生储集空间成因及其四阶段演化——以准噶尔盆地滴西地区石炭系为例

The formation mechanism and four-stage evolution of volcanic primary reservoir spaces:a case study of Carboniferous volcanic rocks in Dixi area,Junggar basin

火山岩油气藏通常具有双重孔隙介质特征,储集空间按成因可划分为原生和次生两大类,绝大多数次生储集空间是原生储集空间经后期成岩作用改造而成。本文通过大量铸体薄片的鉴定和描述,将准噶尔盆地滴西地区石炭系火山岩原生储集空间类型分为气孔、杏仁体内残留孔、粒间孔、粒内孔、晶间孔等5类原生孔隙,以及收缩缝、炸裂缝、砾间缝、晶间缝等4类原生裂缝。综合火山喷发环境、强度及岩石结构构造等影响因素,按照岩浆不同阶段的演化特征,将原生储集空间的形成划分为4个阶段:"岩浆房"阶段、喷溢地表阶段、冷凝成岩阶段及岩浆期后热液阶段。认为岩浆喷溢地表与冷凝成岩阶段是形成原生孔缝的主要时期;岩浆期后热液阶段是减少原生孔缝时期;结晶速度快慢是形成不同类型孔缝的关键。火山岩原生储集空间类型形成机理研究能揭示次生储集空间展布规律,对预测有利储集带意义重大。

Volcanic reservoir is usually of dual porosity medium character.The reservior spaces can be classified into two genetic categories： primary reservior spaces（PRS） and secondary reservior spaces（SRS）,and most of the latter were generated from the fomer by late diagenesis.Based on extensive identification and description of casting thin section,this paper divided the PRS of Carboniferous igneous rocks in Dixi area into five types of primary pores（gas pores,residual amygdale,intergranular pores,intragranular pores and intercrystal pores） and four types of primary fractures（shrinkage joint,explosive fracture,intergravel crack and intercrystal crack）.In combination with the influencing factors such as environment and intensity of eruption and texture and structure of rocks and according to the evolution features of magma at different stages,the formation of PRS is divided into four stages：＂magma chamber＂ stage,outpouring surface stage,diagenetic stage of condensation and deuteric hydrothermal stage,of which the outpouring surface stage and diagenetic stage of condensation were the main periods to form primary apertures while the hydrothermal stage was the period when the number of apertures was reduced.The speed of crystallization constituted the key factor for the formation of different types of PRS.The study of the formation mechanism of igneous PRS can reveal the distribution of SRS and is of great significance in the prognosis of favorable reservoir zones.