欠平衡下牙轮钻头牙齿侵入系数及钻速研究

Study on the Tooth Invasion Coefficient of Cone Bit and Penetration Rate in Under-balance Drilling

欠平衡条件下,钻井机械钻速大幅度提高,但钻头牙齿的侵岩机理至今尚不清楚以岩石侵入理论为基础,在考虑欠平衡钻进条件下,针对牙轮钻头侵岩、破岩问题展开研究,推导了欠平衡钻进井底条件下牙轮钻头牙齿的侵入系数方程,并进一步建立了欠平衡钻进条件下的钻速模型。岩石侵入系数不受牙齿载荷和侵深的影响,是一个描述岩石抗侵入能力的基本参数。以徐深气田为例,理论和实验分析了内摩擦角和刃尖角对侵入系数和机械钻速的影响。结果表明,随井底有效法向应力的增大侵入系数增大;随内摩擦角和刃尖角的增大侵入系数呈指数增大;随有效法向应力的增大机械钻速明显减小;随内摩擦角和刃尖角的增大机械钻速呈线性减小。

The penetration rate rises rapidly in the under-balanced condition, but the intrusion mechanism of cone bit is unclear. Based on rock intrusive theory and tasking the condition of under-balanced drilling into consideration, we explore intruding rock and breaking rock of cone bit the intrusive coefficient equation of cone bit was derived, and the drilling rate model in the condition of under-balanced drilling was built. The rock intrusive coefficient is a basic parameter which describes the intrusion- resistant ability of rock, which is not affected by tooth load and invasion depth. Taking Xushen Gas Field as an example, we make theoretical analysis of the impact of angle of internal friction and bit angle on intrusive coefficient and penetration rate. And the experiment results show that with the increase of effective normal stress of down-hole, and the increase of angle of internal friction and bit angle, the intrusive coefficient increases; with the increase of effective normal stress, the penetration rate decreases obviously, and with the increase of angle of internal friction and bit angle, the penetration rate decreases linearly.