利用测井信息计算页岩有机质丰度——以川南长宁地区龙马溪组为例

Using log data to calculate the organic matter abundance in shale:a case study from Longmaxi Formation in Changning area, southern Sichuan Basin

充足的有机质是油气生成的物质基础,有机质丰度决定了烃源岩的生烃潜力,因此获取页岩有机质丰度对指导页岩气的勘探开发具有重要作用。在选取川南长宁地区龙马溪组下段泥、页岩作为研究对象的同时,利用总有机碳含量作为有机质丰度评价指标,对泥、页岩样品化验得出的有机碳含量和对应深度的测井数据进行拟合,得出总有机碳含量的计算公式,并依据不同测井响应参数的选取,总结出3种测井计算方法,相应地回归出3个计算公式,在研究区对计算结果进行验证和误差分析。结果表明:Δlg R-密度法和密度-铀多元回归法得出的有机碳含量与样品实测的有机碳含量符合程度较高;单井纵向上表现出龙马溪组有机碳含量在下段底部附近较高,具有由底部向上逐渐降低的趋势;密度-铀多元回归公式计算的误差最小,表现出较强的适用性,可在长宁地区推广应用。

Sufficient organic matter is the material base of hydrocarbon generation. Hence, the potential of hydrocarbon generation highly depends on the organic matter abundance. To obtain accurate organic matter abundance in shale is important for the exploration and development of shale gas. Taking the shale in the lower section of Longmaxi Formation in Changning area in southern Sichuan as an object, and considering TOC content as the evaluating parameter of the organic matter abundance, this paper worked out three calculation formulas for getting TOC content according to the correlation between d ifferent well logging data and testing TOC content, then verified the calculation results and analyzed the error. The result shows that the formulas of Δ lg R-DEN method and DEN-U multiple regression method are with larger correlation coefficients and the calculation results coincide well with the TOC content of sample analysis. In single well, at the bottom of the lower section of Longmaxi Formation, the TOC content is higher than that in the upper part and it obviously decreased from bottom to top. The result of DEN-U multiple regression method shows the minimum error and strong adaptability, it can be widely applied in Changning area.