水下喷发火山碎屑岩储层特征及主控因素:以新西兰Taranaki盆地中新世Kora火山为例

Characteristics and controlling factors of volcanic reservoirs of subaqueous pyroclastic rocks:An analysis of the Miocene Kora Volcano in the Taranaki Basin,New Zealand

新西兰Taranaki盆地中新世Kora火山是海底喷发形成的碎屑岩型火山,可代表浅埋藏火山岩的储层特征。本文根据5口钻井的孔隙度、渗透率、孔隙孔径和铸体薄片开展Kora火山的储层特征、储集空间组成、缝宽以及原生和次生孔隙之间关系的分析。研究结果如下:(1)储集空间主要为次生孔隙,然后是裂缝和原生孔隙;Kora火山具有高孔隙度和高渗透率特征,孔径具有双峰到单峰的分布特征。(2)炸裂缝、淬火缝和粒间孔形成于岩浆破碎和/或喷发期间;在晚Tortonian期间产生了网状构造裂缝,在Tortonian晚期至Messinian早期产生规则构造裂缝,二者形成时间均早于原油充注;筛状孔和铸模孔应由风化阶段和/或埋藏阶段的溶蚀作用形成,晶间微孔应由埋藏阶段的蚀变和/或重结晶作用形成。(3)原生孔隙控制次生孔隙的分布,特别是原生的裂缝;在Kora火山中控制筛状孔和铸模孔形成的缝宽的阈值约为9μm,较宽的裂缝可优先促成筛状孔和铸模孔的形成。(4)再搬运火山颗粒含量的增加会显著降低高孔隙度岩石的总孔隙度;近源相带的孔隙度和渗透率高于远源相带,海底喷发火山远源相带发生的强烈钙质胶结可显著减少孔隙度和渗透率。相关认识可为火山岩储层形成、演化和分布规律研究提供依据。

A clear understanding of the reservoir characteristics and formation process is important for analyzing the distribution of favorable reservoirs and evaluating their qualities.However,the multi-component and multi-feature characteristics of volcanic rocks can complicate the reservoir formation process.Here,we used a dataset of porosity,permeability,pore aperture and thin section from 5 boreholes to analyze the reservoir characteristics,components of void space,fracture aperture and relationship between the primary and secondary porosities in the Kora Volcano.The followings are the results:Firstly,the porosity is mainly contributed from secondary pores,followed by fractures then primary pores.The Kora Volcano has high porosity and permeability and bimodal to unimodal pore aperture.Secondly,the microfractures should have been generated during the magma fragmentation and/or eruptive period(s).The macrofractures were generated by the compressional tectonism and had existed before the oil charging.The sieve and moldic pores should have been generated during the weathering and deep burial stages.The intercrystal micropores were generated by the alteration and/or devitrification diagenesis during the burial stage.Thirdly,the primary porosity controls the secondary porosity.The threshold value of fracture aperture for generating sieve and moldic pores is ca.9μm in the Kora Volcano.The bigger aperture of fracture appeared prior to the sieve and moldic pores.And finally,the increasing content of non-juvenile particles could remarkable decrease the total porosity,especially in high porosity rocks.The porosity and permeability of proximal belt are higher than those of distal belt.The calcite cementation also reduced the porosity and permeability of tuffaceous sedimentary rocks,especially in the distal belt of submarine eruption volcano.The findings presented in this work can provide insights into the origin,evolution and distribution of volcanic reservoirs.