Lin Zhenzhou, Pan Heping, Fang Hui, Gao Wenli, Liu Dongming
Institute of Geophysics and Geomatics, China University of Geosciences (Wuhan), Wuhan, 430074, China.
Institute of Geophysical and Geochemical Exploration, CAGS, Langfang, 065000, China.
Sci Rep. 2018 Aug 22;8(1):12596. doi: 10.1038/s41598-018-30795-x.
The Muli area is the only permafrost region on the Chinese mainland wherein gas hydrates have been discovered. The gas hydrates are present in the fractures and pore spaces of the host rocks with a lamellar or micro-disseminated structure. By combining conventional and image logs, we describe the thickness of the permafrost layer and the well log responses of the gas hydrate reservoir, and calculate the porosity and gas hydrate saturation. We then analyze the advantages and disadvantages of different logging methods for evaluating gas hydrate reservoirs. Our results indicate that (1) gas hydrates are present below the permafrost in the Muli area, (2) gas hydrates predominantly occur in rock fractures, (3) the apparent resistivity is sensitive to gas hydrates present in pore spaces, and both apparent resistivity and acoustic logs are sensitive to gas hydrates present in fractures, (4) a density log is more appropriate for calculating porosity, and (5) gas hydrate saturation can be effectively calculated by the Archie equation, the modified Archie equation, and the Indonesian equation.
木里地区是中国大陆唯一发现天然气水合物的多年冻土区。天然气水合物赋存于储层岩石的裂缝和孔隙中，呈层状或微分散状结构。通过结合常规测井和成像测井，我们描述了多年冻土层的厚度和天然气水合物储层的测井响应，并计算了孔隙度和天然气水合物饱和度。然后，我们分析了不同测井方法在评价天然气水合物储层方面的优缺点。我们的结果表明：（1）木里地区天然气水合物存在于多年冻土之下；（2）天然气水合物主要赋存于岩石裂缝中；（3）视电阻率对孔隙中存在的天然气水合物敏感，视电阻率和声波测井对裂缝中存在的天然气水合物均敏感；（4）密度测井更适合计算孔隙度；（5）利用阿尔奇方程、修正阿尔奇方程和印度尼西亚方程可有效计算天然气水合物饱和度。
