鄂尔多斯盆地东缘上古生界页岩特征及含气量

Characteristics and Calculation Method for Gas Content of Upper Paleozoic Shales in the Eastern Margin of Ordos Basin

鄂尔多斯盆地上古生界石炭—二叠系海陆过渡相泥页岩发育,前人对盆地内上古生界泥页岩已做了多项研究,而盆地东缘钻井资料较少,研究程度较低。为了弄清盆地东缘泥页岩的特征及含气性,通过野外实测剖面台头剖面的沉积、地化、岩性、物性等参数并结合等温吸附、核磁共振实验结果,对盆地东缘泥页岩进行分析。研究认为:盆地东缘上古生界以太原组发育的泥页岩最佳,厚度25 m左右,有机质丰度较高,处于产气态烃阶段,泥页岩中非膨胀性黏土含量较高,裂缝/微裂缝发育程度较均匀;同时提出了应用深度和有机碳含量计算吸附气量的公式并通过计算有效孔隙度提高了计算游离气量的精度。经鄂尔多斯盆内钻井榆88井的相关数据验证,文中方法所计算的含气量更符合实际情况,且简单实用。

Shale sequences are well developed in the Carboniferous-Permian transition facies, Ordos Basin. Researchers have done many studies on shales in upper Paleozoic of the Ordos Basin. With few drilling data, however, not enough researches have been carried out on the eastern margin of the basin. In order to clarify the characteristic and gas beating of shales in the eastern margin of the basin, according to the characteristic of sedimentary, geochemistry, lithology, physical property and the experiments of isothermal adsorption and nuclear magnetic resonance of samples from Taitou, the shales were analyzed. It is found that Taiyuan formation has the best condition for shale gas formation which is 25 meters thick, abundant in organic matter, and is in the stage of producing gaseous hydrocarbon, the shale is of high content of non swellable clay minerals and equally distributed crack/micro fractures. We also offer the calculation formula of gas adsorption using parameters of depth and content of organic carbon and improve the calculation accuracy of free volume through calculating effective porosity. It has been verified that the calculation of air content conforms to the actual situation, and the method is simple and practical by relevant data from Well Y88 in Ordos Basin.