查干凹陷火山岩裂缝发育特征及其影响因素

Fracture development characteristics and influencing factors of volcanic rocks in Chagan sag

裂缝发育与否是火山岩油气成藏的重要条件之一,裂缝发育特征及影响因素研究方法多为宏观方法,分析结果误差较大。应用岩心精细描述及显微、超微等技术结合统计学方法,对额济纳旗盆地查干凹陷的火山岩裂缝进行研究,结果表明该区火山岩裂缝主要以低角度和水平产状的中小缝为主,裂缝填充率高,非均质性强;微裂缝主要有构造成因的矿物斑晶裂缝和火山岩基质裂缝,非构造成因的火山玻璃裂缝和杏仁体裂缝4种类型。火山岩裂缝发育频率具有随岩石酸性程度增大而提高,随岩层厚度增大而减小的特征,构造作用是裂缝形成的重要因素,区域构造对裂缝的波及范围约5000m,其中二级断层、断裂带对高频裂缝分布区的影响距离至少为700m。

Fracture development is one of the important conditions for hydrocarbon accumulation in volcanic rocks,the research methods of fracture development characteristics and influencing factors are mostly macroscopic ones with great error in analysis results.Core fine description and microscopic and ultramicro and other techniques combined with statistics are applied to study the fractures of volcanic rock in Ejinaqi basin of Chagan sag,the results showed that the volcanic fissures in this area are mainly small and medium fractures with low angle and horizontal occurrence,the fracture filling rate is high and the heterogeneity is strong.Microcracks are mainly composed of four types,that is,mineral phenocryst cracks and volcanic rock matrix cracks of structural origin,volcanic glass cracks and almond body cracks of nontectonic origin.The development frequency of volcanic rock fractures has the feature of increasing with the increase of rock acidity,and decreases with the increase of rock thickness.The tectonic action is an important factor in the formation of fractures,and the spreading range of the regional structure on fractures is about 5 000 m,where the minimum influencing distance of the secondary fault and the fault zone on the high frequency fracture distribution area is 700 m.