利用非平衡态温度测井数据估算地温梯度

掌握真实地温梯度对于深入了解易受温压场控制的天然气水合物赋存状态具有重要意义。在南海天然气水合物钻探区获取的地温梯度主要以海底表层的热流探针方式为主，由于海底表层尚未压实，地层物理属性多呈现高渗透性，易受到海底底流影响，导致了部分地温梯度无法推算到较深地层。而另一方面，井下原位温度测量虽然可获取真实的地温梯度，但其经济成本昂贵并且时效性低。为此本研究依据天然气水合物钻探井位单一非平衡态温度测井数据和钻井进程，在前人的数学模型基础上，尝试现场快速恢复地层地温梯度的操作，并利用有限的原位地温梯度进行对比分析。研究结果表明，该方法在一定程度上具有适用性，当测井温度变化率在较均匀层段（例如A-B段），根据测井进程可大致估算具有参考意义的原始地温梯度。但应用该方法时也须谨慎，避免使用测井温度变化率在非均匀的数据段（例如B-C段），因为模型中受到数学条件而忽略的多种不确定因素的权重，在外部参数环境波动较大时有可能增加，从而减弱了模拟过程中时间因子的主要作用量。

Application of unsteady borehole temperature logging data to estimation of thermal gradients in the sediments

It is significant to know the actual thermal gradients in sediments for complete understanding of occurrence of gas hydrates which are mostly affected by temperature and pressure regime. The thermal gradients in the gas hydrate drilling area of the South China Sea are almost obtained by needle temperature probes into the nearly seafloor sediments. But due to poorly consolidated condition and high permeability, the physical properties of seafloor sediments are more likely influenced by deep fluid drifting, thus rendering the extrapolations of some thermal gradients unreliable. Alternatively, in situ temperature measuring performed in the boreholes does obtain the actual thermal gradients of sediments, but with high cost and low efficiency that is often not affordable in the offshore drilling projects. To tackle the above problem, based on the previous computational model we utilize the single unsteady borehole temperature logging data and procedures to try to quickly reconstruct the actual thermal gradients. We also compare those reconstructed results with limited in situ thermal gradient measurements acquired by stationary temperature probes. The research shows that this method is valuable and practical when it applies to the section corresponding to smooth temperature variation such as in A-B interval. However, the modeled results are inaccurate in such uneven temperature variation as shown in B-C interval. We propose to be cautious with the method. The weights of other tedious factors that are omitted for the convenience can be increased when the environment of parameter system varies harshly, thus overwhelming the time-factor and reducing the rationality and reliability of the computation model.