鄂尔多斯盆地东缘煤层气储盖特征及其控气作用

煤层气储盖组合在一定程度上控制煤层气的保存条件。依据煤层顶(底)板的封盖能力,将鄂尔多斯盆地东缘煤层气储盖组合划分为4种类型。优势储盖组合主要发育于保德-临县地区太原组泻湖、潮坪相带以及大宁-吉县地区山西组滨浅湖相带,对煤层气的封盖能力强。次优势储盖组合主要发育于保德-河曲地区太原组、石楼-三交地区山西组以及韩城-合阳地区三角洲前缘相带,对煤层气的封盖能力较强。一般储盖组合主要发育于三交-吉县地区太原组浅海陆棚相带、保德-临县地区山西组三角洲平原、河流泛滥盆地相带,对煤层气的封盖能力较弱。不利储盖组合主要发育于河曲以北山西组辫状河上游、冲积扇相带,对煤层气的封盖能力差;煤层气储盖组合类型在一定程度上控制煤储层含气量分布,是煤储层含气性预测的重要参考依据。

CBM reservoir-cap formation type and its gas controlling function in the eastern margin of Ordos basin

The preservation conditions of CBM are controlled by the reservoir-cap formation type to some extent. By analyzing the seal capacity of the seam roof and floor, CBM reservoir-cap formation type in the eastern margin of Ordos basin can be divided into 4 types. The first best reservoir-cap combination type is mainly developed in Taiyuan Formation in Baode-Lin Counties, and Shanxi Formation in Daning-Ji Counties, the former Formation is characterized by lagune-tidal flat facies, the latter Formation is shallow lake facies, which is favorable for CBM preservation. The second combination type is chiefly developed in Taiyuan Formation in Baode-Hequ area, Shanxi Formation in Shilou-Sanjiao area, and the above two formations in Hancheng-Heyang area, the sedimentation is of delta front facies, which is relatively good for CBM preservation. The third combination type developed in Taiyuan Formation in Sanjiao-Ji counties is continental shelf facies, and in Shanxi Formation in Baode -Lin counties is deltaic plain and flood-plain facies, these deposition types have weak sealing ability for CBM. The fourth and the poorest combination type is distributed in Shanxi Formation in the region north of Hequ area, whose deposition is upstream of braided river facies and alluvial fan facies, which is not favorable for CBM preservation. The reservoir-cap formation types are closely related to the gas concentration in the study area, so it is one important reference to forecast CBM abundance of the coal reservoir.