考虑有机质校正的页岩气储层总孔隙度测井评价方法

A logging interpretation method for total porosity considering organic matter correction of shale gas reservoirs

准确计算总孔隙度是页岩气储层测井精细评价的关键之一。以涪陵焦石坝地区五峰—龙马溪组页岩气储层为例,依据AA1井元素俘获测井、常规测井数据、岩芯分析总孔隙度和总有机碳实验数据,分析了Herron总孔隙度模型的适用性,研究认为:模型不能准确计算目标区块层位的总孔隙度,原因在于:(1)视密度孔隙度和视中子孔隙度的计算中,将岩石等效为骨架和孔隙两部分,忽视了页岩储层有机质的存在;(2)模型中的权值系数是依据有限岩芯数据通过最小二乘法拟合得到,有一定的区域适用性。在此认识的基础上,提出了一种改进的评价页岩气储层总孔隙度方法,将该方法应用到焦石坝地区五峰—龙马溪组页岩气储层XX1井的总孔隙计算中,相对于Herron总孔隙度模型,精度有了明显的提高,且该方法操作简单。

The calculation of total porosity is the key to the logging evaluation of shale gas reservoirs. On the basis of element capture, conventional log data, total porosity and the total organic carbon experimental data of AA1 well of the Wufeng-longmaxi formation in Jiaoshiba area, the applicability of Herron＇ s total porosity model is analyzed. The results show that the model can not accurately calculate the total porosity of the target block. The reasons are ： ① When calcu- lating apparent density porosity and apparent neutron porosity, the rock is equivalent to the skeleton and the pore, and the existence of organic matter is ignored. ② In the model, the weight coefficient is acquired from the least square method with limited core data, thus making it has certain regional applicability. Based on the above, an improved meth- od for evaluating the total porosity of shale gas reservoirs is proposed. Applying this method to XX1 well of the Wufeng- longmaxi formation in Jiaoshiba area, the results show that compared with Herron＇ s model, the accuracy of calculating the porosity of the improved model is obviously enhanced. The method is easy to be used.