Tectonic fractures in the Lower Cretaceous Xiagou Formation of Qingxi Oilfield, Jiuxi Basin, NW China Part one: Characteristics and controlling factors
Tectonic fractures in the Lower Cretaceous Xiagou Formation of Qingxi Oilfield, Jiuxi Basin, NW China Part one: Characteristics and controlling factors
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DOI：
10.1016/j.petrol.2016.07.042
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发表时间：
2016-10
影响因子：
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通讯作者：
Wei Ju;Weifeng Sun
中科院分区：
文献类型：
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作者：
Wei Ju;Weifeng Sun
青西油田下白垩统下沟组是中国典型的低孔低渗储层。下沟组裂缝在油气勘探开发中起着重要作用。利用常规岩心、薄片、成像测井等分析资料，确定了下沟组构造裂缝特征及控制因素。下沟组构造裂缝以未充填为主，裂缝孔径小于1.0×10−4m。构造裂缝的主要走向为北东—西南和北西—东南方向。68.8%的构造裂缝为层理裂缝，其次为斜缝（18.2%）和垂缝（13.0%）。不同地区构造裂缝密度差异较大。确定了下沟组构造裂缝的控制因素，包括构造和非构造因素，并对其进行了定性或半定量分析。构造因素分析表明，构造裂缝在应力梯度较大或离断层较近的地区更容易形成（或裂缝密度较高）。在相同的构造背景和应力场下，岩性和矿物组成等非构造因素成为控制构造裂缝发育的主导因素。非构造因素分析表明，构造裂缝在白云质泥岩中最为发育。裂缝密度与下沟组岩石中脆性矿物的比例呈正相关。
The Lower Cretaceous Xiagou Formation of Qingxi Oilfield is a typical reservoir with low porosity and permeability in China. Fractures within the Xiagou Formation play an important role in the petroleum exploration and development. In the present study, analysis data of conventional drill core, thin section and imaging logging were used to determine the characteristics and controlling factors of tectonic fractures in the Xiagou Formation. The majority of tectonic fractures in the Xiagou Formation were unfilled, and their apertures were less than 1.0×10−4m. The dominant strikes of tectonic fractures were in the NE-SW and NW-SE directions. Approximately 68.8% of tectonic fractures were bedding fractures, followed by oblique fractures (about 18.2%) and vertical fractures (about 13.0%). In different places, the densities of tectonic fractures varied greatly. The controlling factors, including tectonic and non-tectonic factors, for tectonic fractures in the Xiagou Formation were confirmed, which have been analyzed qualitatively or semi-quantitatively. Analysis of tectonic factors indicated that tectonic fractures were more probably formed (or the fracture density was high) in regions with larger stress gradients and/or closer to faults. Within the same tectonic setting and stress field, non-tectonic factors of the lithology and mineral composition became the dominant factors governing the development of tectonic fractures. Analysis of non-tectonic factors showed that tectonic fractures were most developed in dolomitic mudstone. The fracture density was positively related to the proportion of brittle minerals in rocks of the Xiagou Formation.