塔里木盆地巴楚凸起H气田奥陶系裂缝主控因素及演化序列研究

THE MAIN CONTROLLING FACTORS AND EVOLUTIONARY SEQUENCE OF ORDOVICIAN FRACTURE IN H GAS FIELD OF BACHU UPLIFT,TARIM BASIN

塔里木盆地巴楚凸起H气田奥陶系储层是低孔低渗裂缝型碳酸盐岩储层,裂缝系统作为储层渗流通道,其空间分布和主要控制因素复杂,具有多期次叠加和演化的特征。文章采用岩心描述、镜下观察、成像解释等手段分析H气田奥陶系碳酸盐岩裂缝发育特征,明确裂缝主要控制因素,建立了裂缝演化序列。结果表明:巴楚凸起H气田奥陶系以剪切缝为主,张性缝次之,张剪缝最少,裂缝发育的主要控制因素为断层、褶皱及岩性等,与断层相关的裂缝主要发育在距断层460 m的范围内;地层变形程度越强,裂缝越发育;裂缝发育程度还受岩性的控制,灰岩的粒径或晶粒越大,构造裂缝越发育。根据已有碳氧同位素测试研究成果,并结合岩心观察发现:H气田奥陶系构造裂缝至少经历了三期演化活动,分别为加里东运动中期少量低角度北东东向和北北西向剪切缝发育期,海西运动晚期中—高角度北西西向张性缝和北东东向、北西向张剪缝以及南北向、北东向中—高角度剪切缝发育期,喜马拉雅运动早期大量高角度北东东向、北北东向剪切缝发育期,主要造缝期为喜马拉雅运动早期。

The Ordovician reservoirs in H gas field of Bachu uplift in Tarim Basin are carbonate reservoirs with low porosity and low permeability. The fracture system, as reservoir percolation channel, is characterized by complex spatial distribution and main control factors, and features of multi-stage superposition and evolution. Fracture development characteristics of Ordovician carbonate rocks in H gas field are analyzed by means of core description, microscopic observation and imaging interpretation, etc., major controlling factors of fractures are identified, and fracture evolution sequence is established. The results show that, the Ordovician system of H gas field in the Bachu uplift is dominated by shearing fractures, followed by tensional fractures, and tensional-shearing fractures are the least. The main controlling factors of fracture development are faults, folds and lithology, etc., and fault-related fractures are mainly developed within the range of 460 m from the fault. The higher the deformation degree is, the more developed the fractures are. Also the degree of fracture development is controlled by lithology. The larger the particle size or grain size of limestone are, the more developed the structural fractures are. According to the carbon and oxygen isotope test, combined with core observation, it is found that Ordovician tectonic fractures in H gas field have undergone at least three periods of evolution: development period of a small amount of low angle NEE and NNW trending shearing fractures in the middle of Caledonian;development period of medium-high angle NWW trending tensional fractures, NEE and NW trending tensional-shearing fractures, and SN and NE trending medium-high angle shearing fractures in late Hercynian;development period of a large amount of high angle NEE and NNE trending shearing fractures in early Himalayan, which is the main generation period of fractures.