取样钻头在水合物岩层中破岩温度场仿真模拟

Analog Simulation of Temperature Field for Sampling Bit in Hydrate-bearing Formations

通过地质钻探对赋藏岩心进行取样是最为直观有效的水合物勘探方法。钻头钻进过程中往往会产生较高的温升,天然气水合物赋藏岩层对外界条件又具有非常高的敏感性,其周围温度和压力条件的改变会使水合物分解。为此,建立有限元模型并对钻头破岩过程进行仿真模拟,重点研究了取样钻头、水合物赋藏岩层以及岩心样品的温度分布和变化情况。研究结果表明,取样过程中温升较高的区域主要集中在井底,最高温升在井底呈散点状分布;钻头钻进时切削齿前端面尖点首先与岩层接触产生摩擦热,热量由尖点向内部传递导致温度梯度;钻速越高,钻头转速越快,岩层温升越高;钻探取样过程中摩擦热本身对岩心样品温升的影响较小,实际操作时应注意后续提钻作业中的保真保压。

Sampling of cores in reservoir formations during geologic exploration can be seen as the most intui- tive and effective way to explore hydrates. During the course, movements of drill bit may lead to significant increa- ses in temperatures, whereas reservoir formations for natural gas hydrate are usually very sensitive to external con- ditions. Changes in surrounding temperatures and pressures may lead to dissolution of hydrates. To deal with the problem, finite element models have been established to facilitate analog simulation of formation penetration by the drill bit. Relevant researches are performed to determine distribution and changes in temperatures of sampling bits, hydrate reservoir formations and core samples. Research results show areas with higher temperatures during sampling period distributed predominantly at the bottom, whereas points with the highest increases in temperatures distribu- ted sparsely at the bottom; during drilling, tips of cutting teeth may contact with the formation and generate heat through friction. Such heat may be transmitted from the tip to internal section of the bit and during the course may form temperature gradient; higher ROPs may indicate higher rotation speeds of the bit and higher temperatures in the formation. During drilling operations, heat generated by friction during drilling has minor impacts to increases in temperatures of the core. Cares shall be taken during field application to maintain desirable pressures in future trip- ping operations.