鄂尔多斯盆地北部深盆气藏近地表地球化学特征

The Geochemistry Characteristics Near the Earth Surface in Deep Basin Gas Reservoirs of Northern Ordos Basin

鄂尔多斯盆地北部上古生界气藏为深盆气藏。它自南到北可分为气区和水区;气区分布在南部近源岩区,其成藏受控于砂岩展布和物性,气藏压力“负异常”,无边水和底水,烃类向上微扩散弱,近地表地球化学背景场低;水区分布在该区北部,远离源岩,其成藏主要受控于构造,气藏压力正常,具有边水或底水,烃类向上微扩散较强,近地表地球化学背景场相对较高。根据这种特征,建立了深盆气藏气水界面的地球化学特征以及气区和水区的异常模式,即由低背景突变为中背景的陡增带为深盆气气藏的气水分界面,水区气藏主要为环状或半环状异常模式。

The upper Palaeozoic reservoirs in the northern Ordos Basin are deep basin gas reservoirs. It can be divided into gas reservoirs and water areas from the south to north. Gas areas distribute in the south near source and hydrocarbon accumulation are controlled by the distribution and physical properties of the sandstones, pressure in the gas reservoirs indicates negative abnormity without marginal water and bottom water. The upward and microscopic diffusion of hydrocarbon is weak, near-surface geochemistry background field is low, the water area is distributed in the north, which is far from the source rocks, and its hydrocarbon accumulation is controlled by the structure, pressure in the gas reservoirs is normal with marginal water and bottom water. Hydrocarbon is strongly diffused upward, where near-surface geochemistry background field is relatively weaker. Based on the characters stated above, the geochemistry characteristics and abnormal patterns between gas and water areas are established for gas-water interface of deep basin reservoirs. The abnormal pattern is that the steep background area is the gas-water interface of the deep basin gas reservoirs, and the gas reservoirs in the water areas are mainly the circular and semi-circular abnormal patterns.