钻井液矿化度对康村组泥岩强度特征的影响研究

以西部某区块康村组地层泥岩为研究对象,进行了X射线衍射实验、环境扫描电镜实验、阳离子交换实验、不同矿化度的KCl溶液和钻井液浸泡后的泥岩单轴压缩实验。得到康村组泥岩矿物组成、微观结构特征、水化膨胀能力大小、不同矿化度的KCl溶液和钻井液浸泡后的泥岩强度参数;研究了钻井液矿化度对该地区泥岩强度的影响,分析了不同矿化度钻井液作用下泥岩的强度特征变化。研究结果表明:泥岩微孔洞及微裂缝发育,矿物成分主要为石英、长石以及黏土矿物;黏土矿物含量较高,有较强度的水化膨胀能力。KCl溶液或钻井液浸泡后,泥岩峰值强度降低,随着溶液或钻井液矿化度降低,泥岩峰值强度点对应径向、轴向应变变大,泥岩由脆性向延性转化。KCl溶液或钻井液的矿化度大小与其浸泡后的泥岩单轴抗压强度、弹性模量在一定范围内皆呈近线性正比关系,与其泊松比呈线性反比关系;随着溶液或钻井液的矿化度增加,泥岩抗压强度、弹性模量皆随之增大,泊松比随之减小。研究结果可应用于现场施工,通过改变钻井液矿化度提高泥岩强度,避免钻进过程中井壁失稳。

Study on Influence of Drilling Fluid Mineralization Degree on Strength Characteristics of Kangcun Formation Mudstone

X-ray diffraction experiments, environmental scanning electron microscopy experiments, cation exchange experiments, uniaxial compression experiments after soaking of KCl solution and drilling fluid with different salinity were carried out on the mudstones of the Kangcun Formation in a block in the west. The mineral composition, microstructure characteristics, hydration expansion capacity, strength parameters of mudstone after immersion in KCl solution and drilling fluid with different salinity were obtained. The influence of drilling fluid salinity on the strength of mudstone in the area was studied. The variation of strength characteristics of mudstone under different mineralization drilling fluids was analyzed. The results show that the micro-cavities and micro-cracks of mudstone are developed. The mineral composition is mainly quartz, feldspar and clay minerals. The clay mineral content is high and the hydration expansion ability is stronger. After immersion in KCl solution or drilling fluid, the peak strength of mudstone decreases. As the mineralization degree of solution or drilling fluid decreases, the radial and axial strain in peak strength point of mudstone increased with it, and the mudstone transforms from brittle to ductile. The salinity of KCl solution or drilling fluid has a nearly linear proportional relationship with the uniaxial compressive strength and elastic modulus of the soaked mudstone within a certain range, and it has a linear inverse relationship with its Poisson's ratio. As the salinity increases, the compressive strength and elastic modulus of the mudstone increase, and the Poisson's ratio decreases. The research results can be applied to on-site construction. The mudstone strength is improved by changing the mineralization degree of the drilling fluid to avoid the instability of the borehole wall during the drilling process.