徐家围子断陷火山岩储层裂缝发育特征及主控因素

徐家围子断陷火山岩储集物性明显受裂缝发育程度的影响。根据相似露头区野外调查、岩心观测以及铸体薄片和成像测井分析等资料,并结合应力场数值模拟技术,对该区火山岩储层裂缝的类型、走向、倾角、长度、密度、充填性以及影响裂缝发育程度的主控因素进行了分析。结果表明,研究区火山岩裂缝主要以构造剪切裂缝为主,其次为成岩裂缝;主要发育近东西向、近南北向、近北东向和近北西向4组裂缝;裂缝多为有效裂缝,很少被充填;以高角度和斜交裂缝为主,长度和密度变化较大。影响该火山岩储层裂缝发育程度的主控因素包括古构造应力、岩性、火山机构和断层等,其中古构造应力的高值区与裂缝较发育部位具有良好的匹配关系;在多种火山岩中,粗面岩、集块岩和流纹岩裂缝较发育;裂缝多发育在火山口和近火山口相组;在应力扰动作用明显的断层上盘裂缝较发育,且随着与断层距离的增大,裂缝发育程度不断降低。

Fracture development characteristics and main controlling factors of the volcanic reservoir in Xujiaweizi fault depression

Reservoir physical properties of volcanic rocks in Xujiaweizi fault depression are influenced obviously by the fracture developing extent. According to the survey of similar outcrops, the core observation, casting thin slice and imaging logging analysis data, in combination with stress field numerical simulation technology, the authors analyzed fracture types, trends, dip angles, lengths, densities, fillings and the factors influencing the fracture development of the volcanic reservoir. The result shows that fractures in the study area are mainly tectonic shear fractures, followed by diagenetic fractures. Four nearly WE-, NS-, NE-and NW-trending fracture groups are developed, mainly high angle fractures and inclined fractures, and the lengths and densities of these fractures change significantly. The main factors influencing the development of the volcanic rock fractures include ancient tectonic stress, lithology, volcanic edifice and fault. Therefore, the high value area of the ancient tectonic stress has good relationship with fracture developed area. In a variety of volcanic rocks, fractures in trachyte, agglomerate and rhyolite are relatively well developed. Fractures are mainly developed in the facies of volcanic crater and near-crater. Fractures are also developed on the upper wall of the fault with obvious stress disturbance and, with the increase of the distance from the fault, the extent of the fracture development decreases.