随钻D-T中子孔隙度测井低灵敏度和岩性影响校正方法研究

为了提高随钻氘-氚(D-T)中子孔隙度测井的测量精度,通过研究其在多种岩性、孔隙度地层中的响应,对比与化学源的响应差异,分析所测孔隙度灵敏度及精度偏低的原因,并提出对应的校正方法。结果表明:由于D-T源能量较化学源高,地层密度对含氢指数测量影响增强,使得随钻D-T中子孔隙度测井地层孔隙度灵敏度偏低,且受到泥页岩效应的影响较大;密度校正后,地层孔隙度灵敏度显著提高,且受到岩性的影响降低,尤其是泥页岩效应几乎被完全消除。因此,通过对随钻D-T中子孔隙度测井结果的校正,测量灵敏度和精度都得到大幅提高,可以较好地替代化学源测量地层中子孔隙度。

Correction method of low sensitivity and lithology effect of D-T neutron porosity logging-while-drilling

In order to improve the measurement accuracy of Deuterium-Tritium (D-T) neutron porosity logging-while-drilling, different responses in several types of formations were measured using the Deuterium-Tritium (D-T) accelerator and the Am-Be source, and the differences in the measured responses were compared. In addition, the causes of the lower porosity sensitivity and accuracy were analyzed, and a correction method was proposed. The results show that the energy of neutron emitted by D-T neutron generator is higher than that by the chemical source, and the influence of formation density on hydrogen index is higher than the chemical source. So the porosity sensitivity of the D-T neutron logging-while-drilling is much lower than the chemical neutron source, and the effect of shale on the measurement is high. On the other hand, after applying density correction, the porosity sensitivity is significantly improved, and the lithology effects are reduced as well especially in the shale formation. It is concluded that the chemical sources can be replaced by more accurate and sensitive density-corrected D-T neutron porosity logging-while-drilling technique.