冲旋钻井条件下的岩石破碎机理

冲旋钻井因其具有较高的钻速和较小的井斜,而广泛应用于矿山、石油与天然气领域的钻井工程中.为了揭示冲旋钻井的破碎机理,考虑静压、冲击和旋转的耦合作用,分别建立了牙齿和12 1/4″全尺寸平底钻头与岩石的三维冲击动力学模型.对所建立的模型进行有限元求解,结果显示:拉应力破碎是岩石破碎的主要形式,剪切应力、压应力破碎次之;岩石的破碎主要发生在岩石的拉应力失效阶段和卸载后的静压-旋转剪切破岩阶段;岩石在单齿的作用下可以显著地分成4个半球形区域;全尺寸钻头的破岩过程可以分成5个破碎阶段;边齿倾角越大,破岩侵深越小,破碎体积越大,齿顶应力越高;钻头边齿齿顶和齿孔应力均远高于中心齿,极易最先破坏;岩石越硬,牙齿侵入深度越小,破岩体积越大.研究结果与一系列的室内实验研究结果一致,可用于冲旋钻井钻头的优化设计及冲旋钻井参数的优选.

Rock-breaking Mechanism of Rotary-percussive Drilling

In order to reveal the physical mechanism of rotary-percussive drilling process,coupling the weight on bit(WOB),percussion and rotation,we establish two three-dimensional(3D)impact dynamics models of insert and rock,and 12 1/4″ bit and rock respectively.We use the fracture judgment to describe when and how rock fails,and a triangular wave as the percussion stress wave.The calculations of the two models show that:aggressive tensile failure is primarily responsible for the rock breakage,while shear failure(or compressive failure)only contributes as a minor player;rock breaking mainly happens in the tensile failure stage and the WOB and bit rotation stage;the rock under insert rotary-percussion can be divided into four hemispherical zones;the physical mechanism of the bit rotary-percussion drilling process is characterized as five fundamental processes;rock breaking volume and teeth crest stress are proportional to the teeth angle on the inclined plane,but the intrusion-depth of the tooth is inversely proportional to the teeth angle;the teeth crest and hole stresses of the teeth on the inclined plane are higher than the teeth on the flat plane;when the rock is harder,the rock breaking volume is larger and its intrusion-depth is lower.The results are further calibrated with a series of laboratory experiment results.