海相页岩孔隙度GRI测定方法优化

Optimization of GRI porosity determination method for marine shale

孔隙度是研究页岩气储层最基本的参数之一,通常采用美国天然气研究所(Gas Research Institute,以下缩写为GRI)的方法测定页岩总孔隙度。为了解决GRI方法存在的样品总体积测量不准和烘干温度、粉碎粒径大小、饱和压力以及平衡时间等参数缺乏技术规范等问题,选取四川盆地荣昌地区下志留统龙马溪组海相页岩为研究对象,引入材料学科GeoPyc 1360体积测定仪和AccuPyc Ⅱ1340固体密度仪联合测量页岩总孔隙度,探讨样品烘干温度、粉碎粒径、样品洗油、饱和压力和平衡时间等因素对页岩孔隙度测定结果的影响情况。实验研究结果表明:①页岩样品孔隙度测定的最佳烘干温度为110℃,温度过高有可能会改变页岩孔隙结构;②孔隙度测定的最佳粒径为10.00~0.25 mm,粒径过小有可能破坏页岩的骨架结构;③高成熟页岩孔隙度测定样品不需洗油;④最佳饱和压力选择0.66~1.03 MPa,平衡时间不少于10 min。结论认为,通过对孔隙度GRI测定方法优化,实现了页岩不规则样品外观总体积的测量,给出了海相页岩孔隙度测量适宜的预处理条件和测试参数,改进后的方法可以节约钻取柱塞样的成本、缩短测定时间,并且能够满足页岩气勘探开发实验的需求。

Porosity is one of the most basic parameters in the study of shale gas reservoirs.GRI(Gas Research Institute)method is usually adopted to determine the total shale porosity,but it cannot determine the total sample volume accurately and lacks technical specifications on drying temperature,crushed particle size,saturation pressure and equilibrium time.In this paper,the marine shale of Lower Silurian Longmaxi Formation in the Rongchang area of the Sichuan Basin was taken as the research object to solve the above mentioned problems.The Geopyc 1360 volumetric analyzer and AccupycⅡ1340 solid densitometer of material science were introduced jointly to determine total shale porosity.In addition,the influences of sample factors(e.g.drying temperature,crushed particle size,oil washing,saturation pressure and equilibrium time)on the determination result of shale porosity were discussed.And the following experimental results were obtained.First,the optimal drying temperature to determine the porosity of shale samples is 110℃.If the temperature is too high,the shale pore structure may be changed.Second,the optimal particle size for porosity determination is 10.00-0.25 mm.If the particle size is too small,shale's skeleton structure may be destroyed.Third,no oil washing is needed in the samples of high-maturity shale for porosity determination.Fourth,the optimal saturation pressure is in the range of 0.66-1.03 MPa and the equilibrium time is no less than 10 min.It is concluded that by optimizing the GRI porosity determination method,the bulk volume of irregular shale sample can be determined,and the pretreatment conditions and test parameters suitable for determining the porosity of marine shale are provided.The optimized method can save the drilling cost of plug sample,shorten the determination time and meet the experimental requirements of shale gas exploration and development.