摘要
大庆油田嫩江组二段底部与嫩江组一段顶部成片套损严重,从前一直认为泥岩吸水膨胀、蠕变是导致成片套损的主要因素。成片套损位置研究发现,嫩江组二段底部与嫩江组一段顶部成片套损实际集中于嫩江组二段底部标志层内,而嫩江组二段底部标志层岩石矿物学特征综合研究结果表明,其不含遇水膨胀的蒙脱石,且粘土矿物含量也低于其上下相邻岩石,表明其遇水膨胀与蠕变较弱,岩石遇水膨胀与蠕变不会构成成片套损的主要原因。嫩江组二段底部标志层岩石岩心观察描述、镜下鉴定、矿物成分综合测试和岩石强度性质研究发现,嫩江组二段底部标志层泥岩为富含长英质的质地坚硬岩石,含粘土矿物较少,不含蒙脱石,岩石吸水能力差、膨胀与蠕变能力弱;标志层中存在多个化石富集带,化石沿岩石层理分布形成沿层理方向的区域性力学薄弱面;沿化石层层理的抗张强度与抗剪强度远低于其他层位和垂直于层理方向的强度性质。因此,一旦注入水进入嫩江组二段底部标志层,富含化石的岩石沿岩石层理优先发生破坏,并迅速扩展,形成成片套损现象。
There has been a popular opinion that the serious local regional casing impairment between the bottom of N2 （member ~ of the Nenjiang formation） and the upper part of Nl（member I of the Nenjiang formation）in the Daqing Oilfield is caused by water-absorbing, and swelling and creeping of shale. However, the research presented in this article unveils a new mechanism that causes the casing impairment. According to lead impressions and multi-arm calliper results, the position of the local regional casing impairment overwhelmingly locates in the index bed of N2 between the N2 and N1 Formation instead of the bottom of N2 or the upper part of NI. The systematical petrology and mineralogy study shows that the index bed of N2 mainly consists of fine quartz, feldspar, shells of fossils and some clay minerals, but without montmorillonite that causes water- absorbing, swelling and creeping. The content of clay minerals of the index bed of N2 is also less than its adjacent rock. All these show that the swelling and creeping capacity of the index bed of N2 is very poor, which is not the principal factor causing the local regional casing impairment. On the contrary, the index bed of N2 is a kind of hard rock, but within it there are special mechanical weak planes that result from fossils lying on the sediment beds. Rock mechanical experiments show that the tensile strength and shear strength of the mechanical weak planes are far less than that of the sediment beds with a few or no fossils. Therefore, the new mechanism explains that, once injected water reaches the index bed of N2, the fluid pressure and in-situ geostress will break the mechanical weak planes within the index bed of N2. Because very poor water-absorbing and no rock swelling and creeping occur, the broken planes then quickly elongate around the weak plane, inducing the local regional casing impairment.
出处
《地质论评》
CAS
CSCD
北大核心
2006年第4期532-538,i0005,共8页
Geological Review
基金
中石油"十五"重点攻关项目"套损原因综合分析与预测技术"(编号030133-1)资助成果。
关键词
成片套损
嫩江组二段底部标志层
岩石矿物学
力学薄弱面
大庆油田
local regional casing impairment
index bed of N2
petrology and mineralogy
mechanical weak plane
Daqing Oilfield
