声波时差测井扩径影响校正方法在煤层气储层中的适用性分析

Analyzing on applicability of expanding influence correction method of acoustic logging in the coalbed methane reservoir

准确地测量煤层气储层的声波时差是提高煤岩力学参数、地应力计算精度的保障,进而为压裂施工设计提供测井技术支持.煤岩性脆、机械强度低,钻进过程中不可避免地会出现井壁坍塌、扩径,致使声波时差测井值受扩径的影响在所难免.现有声波时差测井扩径影响校正方法多针对的是石油领域的砂泥岩剖面而提出的,专门针对煤层气储层的方法尚不多见,现有方法是否适用于煤层气储层不得而知.鉴于此,本文以鄂东气田韩城矿区为例,采用统计方法对研究区主力煤层的声波时差、井径测井响应特征进行了翔实剖析,发现扩径严重的煤层气储层声波时差较大.通过对常用声波时差扩径影响校正方法进行系统梳理和深入分析,得知其在煤层气储层中的适用性.优选适用性较高的频率法,对研究区煤层气储层进行了扩径影响校正.结果表明,校正结果较实测值低、且与实验室分析化验值较为接近,表明频率法能够较有效地提高声波时差测井扩径影响的校正精度.

It contributes to improve the calculation precision of coal mechanics parameters and the coal stress that accurately measure the acoustic time of Coal bed methane （CBM） reservoir, and also to provide technical support for the fracturing construction design. Coal rock have the characteristics of brittle and low mechanical strength, so in the process of drilling hale there will appear hole-wall collapsing and hole enlargement inevitably, leading to the acoustic time logging value is affected by the hole enlargement unavoidable. Existing correction methods of acoustic logging expanding influence are mostly aimed at the sand-shale sectional of oilfield; specifically for coal bed methane reservoir method is still rare, whether existing method suitable for CBM reservoir is unclear. This paper takes the Hancheng mining area in eastern Ordos basin as an example, detailed analysis acoustic time and caliper log response characteristic of the main coal seams in the studied area using statistical method, found acoustic time is bigger in the hole enlargement of CBM reservoir. Through systematically combing and in-depth analysis for the usual acoustic time expanding influence correction method found that its applicability in CBM reservoir. The frequency method which has high applicability to correction hole enlargement effect of the CBM reservoir in the studied area. It shows that correction result is lower than the measured value and it is close to the laboratory analysis test value, and the frequency method can effectively improve the accuracy of hole enlargement effect for acoustic time log.