鄂尔多斯盆地东缘煤层气储集与产出条件

Preservation and deliverability characteristics of coalbed methane in east margin of Ordos Basin

对鄂尔多斯盆地东缘58件煤岩样品进行块煤光片法显微裂隙测试、低温氮比表面测试和压汞孔隙结构测试.结果表明,鄂尔多斯盆地东缘煤储层孔裂隙系统具有以下特点:显微裂隙密度大多数在20～100条/(9cm2)之间,构造活动强烈地区微裂隙发育增多;煤储层孔隙度相对较小,孔隙结构以小孔和微孔为主,大孔次之,中孔发育最差;BET比表面积总体较高,介于0.092～20.480m2/g,煤储层吸附能力强.运用Q型聚类分析方法,划分出4类具有不同孔隙系统的储层,结合显微裂隙发育情况得出:Ⅰ类储层显微裂隙较发育,孔隙度大,孔隙结构合理,比表面积较高,为煤层气勘探开发的有利储层;Ⅲ类储层构造微裂隙发育,但渗透性差,孔隙度、比表面积较小,中孔不发育,为煤层气勘探开发的不利储层;Ⅱ类储层介于Ⅰ,Ⅲ类储层之间,为煤层气勘探开发的较有利储层;Ⅳ类储层微裂隙发育,孔隙度中等,大、中孔发育,渗透性能较好,但储层比表面积较低,限制了储层的吸附能力,为煤层气勘探开发的较有利储层.

Fifty eight coal samples from east margin of Ordos Basin were examined using the microfracture analysis by fluorescence microscope, liquid nitrogen adsorption analysis and mercury-injection analysis. The results show that the frequency of microfractures in coals is about 20 - 100 strips per 9 cm2, and increases in the tectonically active areas. The porosity is relatively low. The pore is dominated by transition pores and micropores. Macropores take the second places, and mesopores develop least. The BET surface area is relatively high ranging from 0. 092 to 20. 480 m2/g. The coal reservoirs have good adsorption capacity. Four reservoir types with different pore-fracture systems were classified by Q cluster analysis and the difference of reservoir physical property were analyzed. Type I with more microfraetures, large porosity, reasonable pore structure, high specific surface area makes the good reservoir for CBM exploration and development. Type Ⅲ with more structural microfractures, poor permeability, low porosity and specific surface area, less mesopores, is bad reservoir for CBM exploration and development. The characteristics of type Ⅱ are between type Ⅰ and Ⅲ, which makes it to be the relatively favorable reservoir for CBM exploration and development. TypeⅣwhich has the good permeability, but the weak adsorption capacity is relatively beneficial for CBM exploration and development.