塔里木盆地深层致密砂岩气层应力敏感性

深层-超深层致密砂岩气藏是塔里木盆地油气勘探开发的重点对象,其在钻完井和生产过程中经常表现出与井筒液柱压力或井底流压变化十分敏感的复杂工程行为。为了揭示深层致密砂岩应力敏感特征及主控因素,以塔里木盆地3个典型天然气藏(DB、YM、KS)为研究对象,分别开展了模拟围压递增条件下的裂缝和基块岩样应力敏感实验,并基于扫描电镜、铸体薄片、X-射线衍射、高压压汞等分析手段,分析了孔隙结构、矿物组分、裂缝发育特征对深层致密砂岩应力敏感性的影响。结果表明,塔里木盆地深层致密砂岩基块应力敏感系数为0.280 6~0.771 4,应力敏感程度总体为中等偏强-强,其中KS(0.771 4)>DB(0.654 0)>YM(0.579 6);裂缝应力敏感系数为0.532 3~0.806 9,应力敏感程度总体为中等偏强-强,其中YM(0.726 2)>KS(0.693 5)>DB(0.626 5)。深层致密砂岩应力敏感程度受地层埋藏深度、孔隙结构、矿物组成和裂缝发育程度综合因素控制。基块岩样应力敏感程度与储层埋深、不稳定矿物组分含量、黏土矿物含量成正相关,与储层石英含量、孔隙度、渗透率、孔喉半径成负相关。裂缝岩样应力敏感程度主要受裂缝宽度控制,应力敏感程度随裂缝宽度增大而减小。

Stress sensitivity of deep tight gas-reservoir sandstone in Tarim Basin

Deep and ultra-deep tight sandstone gas reservoir is the key exploration and development object of unconventional oil and gas resources in Tarim Basin. In the process of drilling,completion and production,it often shows complex engineering behavior which is sensitive to the change of wellbore fluid column pressure or bottom hole flow pressure. In order to reveal the stress sensitive characteristics and main controlling factors of deep tight sandstone,taking the three gas reseruiroivs in Tarim Basin as examples,the stress sensitivity experiment of fracture and block samples are carried out under simulated increasing confining pressure. By scanning electron microscopy(SEM),the casting thin sections,X-ray diffraction(XRD),high pressure mercury injection,the effects of pore structure,mineral composition and fracture development on stress sensitivity of deep tight sandstone were analyzed. The research results show that the stress sensitivity coefficient of the block rock samples of deep tight sandstone reservoir in Tarim Basin ranges from 0.280 6 to 0.771 4,and the stress sensitivity degree is from moderately strong to strong,which is KS(0.771 4)>DB(0.654 0)>YM(0.579 6). The stress sensitivity coefficient of the fractured samples of deep tight sandstone reservoir in Tarim Basin ranges from 0.532 3 to0.806 9,and the stress sensitivity degree is from moderately strong to strong,which is YM(0.726 2)>KS(0.693 5)>DB(0.626 5). The stress sensitivity of deep tight sandstone is controlled by a combination of factors including depth,pore structure,mineral composition and fracture development. The stress sensitivity of the block rock sample is positively correlated with the depth of the reservoir,the content of unstable mineral components and clay minerals,and negatively correlated with the quartz content,porosity,permeability and pore throat radius of the reservoir. The stress sensitivity of fracture samples is mainly controlled by the fracture width,which decreases with the increase of fracture width.