南海西部海域难钻地层特征及破碎机制研究

近年来，南海西部海域部分油田的下第三系地层机械钻速较慢，严重影响了勘探开发进度，为了降低钻井成本，增加钻井时效，必须掌握该海域难钻地层的特征及破碎机制。首先开展了岩屑矿物组分测定，结合录井资料，掌握了南海西部海域难钻地层的岩性特征。在对难钻地层的破坏强度、硬度、塑性系数、可钻性、研磨性等相关参数室内试验的基础上，建立了该地层岩石力学参数的预测模型，并基于30口测井的资料建立了难钻地层抗钻特性剖面和南海西部海域三维可钻性剖面，揭示了区域难钻地层的分布情况及抗钻特性；为解决难钻地层的工艺技术难题，还进行了难钻地层PDC钻头的破岩机制试验研究，研究了PDC钻头牙齿齿形、钻压和转速对破岩效率的影响。研究发现：北部湾盆地建议提高钻头的攻击性，并采用高转速的动力钻具复合钻进方式；珠江口盆地应提高钻头复合片的耐磨性，采用较高钻压和合理顶驱转速，为更好地控制钻井成本和提高钻井综合经济效益提供技术指导。

Rock mechanical properties and rock breaking mechanism of the complex formation of the western South China Sea oilfields

The rate of penetration(ROP) of some oilfields in the western South China Sea is very slow in recent years,which restricts their exploration and development process.In order to increase the ROP and reduce the drilling costs,the mechanical properties of rock and the rock breaking mechanism should be known precisely.We identify the lithological characters of the complex formations(mostly pebble and interbed formations) by mineral composition identification device(X-ray diffractometer).Laboratory experiments of core uniaxial compressive strength(UCS),hardness,plasticity coefficient,drillability and abrasive property were done;and the prediction models of rock mechanical parameters were established.We plotted the continuous sections of rock mechanical parameters of 30 wells and three dimensional drillability planes using the log data to reveal the complex formations distribution and their rock mechanical properties.According to the complex formations breaking mechanism of the PDC bit,we studied the influence law of the tooth shape,weight on bit(WOB) and revolutions per minute(RPM) of PDC bit on penetrating efficiency of pebble and interbed formations.The results show that for the Northern Gulf Basin oilfields,the bit aggressivity should be improved and the downhole drilling motor with high rotary speed should be used;for the Pearl River Mouth Basin oilfields,the more wearlessness of the PDC bit under higher bit weight and lower rotary speed is suggested,which can reduce the drilling cost and improve the drilling efficiency.