吉木萨尔凹陷芦草沟组致密储集层裂缝特征及主控因素

准噶尔盆地吉木萨尔凹陷芦草沟组致密储集层分布广泛,但勘探开发效果一直不稳定,其重要原因是裂缝的发育特征和主控因素不清楚。在查明裂缝基本特征的基础上,对裂缝形成和分布的主控因素进行探讨。通过野外露头、岩心、岩石薄片、扫描电镜、成像测井、X射线衍射全岩矿物分析等,研究了裂缝与矿物脆性、岩性、有机碳含量、地层厚度、沉积微相的关系。结果表明,研究区芦草沟组裂缝的发育程度与矿物脆性和有机碳含量呈正相关,与地层厚度呈负相关;沉积微相对裂缝的影响较为复杂。综合矿物脆性、岩性、有机碳含量和地层厚度的因素,在滨湖沉积相中,白云质砂坪和砂坝微相裂缝发育;三角洲沉积相中,远砂坝和席状砂微相裂缝发育,这些沉积微相是裂缝发育的有利相带。

Fracture Characteristics and Main Controlling Factors of Tight Reservoirs in Lucaogou Formation of Jimsar Sag,Junggar Basin

The tight oil reservoirs of the Lucaogou formation are widely distributed in the Jimsar sag of Junggar basin, Northwest China. However, the effects of its exploration and development are unstable because the fracture development characteristics and main controlling factors on fractures are not verified. This study aims to clarify the basic characteristics of fractures and study the main controlling factors on fractures. Based on the data analysis of outcrop, core, rock thin section, SEM, image logging and X-ray diffraction, the paper studies the relationships of fractures with mineral brittleness, lithology, total organic carbon content, stratum thickness and sedimentary microfacies. The study results indicate that the development of the fractures in Lucaogou formation is positively correlated with mineral brittleness and TOC content, and negatively correlated with stratum thickness. The influence of sedimentary microfacies on fractures is complex because the factors of mineral brittleness, lithology, TOC content and stratum thickness should be comprehensively considered. Dolomitic sand flat and sand bar are the developed in the shore-lacustrine facies, while distal sand bar and sheet sand are developed in the delta facies, all these microfacies are favorable for fracture development.