二连盆地致密油形成特征及勘探潜力

The Formation Characteristics and Exploration Potential of Tight Oil in Erlian Basin

二连盆地普遍发育低孔、低渗透性储层,位于洼槽区及构造翼部的下白垩统巴彦花群腾格尔组下段与巴彦花群阿尔善组顶部特殊岩性段与致密砂砾岩段储层尤为致密,空气渗透率一般小于0.5 mD。巴彦花群腾格尔组下段与巴彦花群阿尔善组顶部发育含云灰质为特征的特殊岩性段和湖相黏土质泥岩两类优质烃源岩,致密储层与优质烃源岩构成源储一体或互层状分布,利于油气就近运移成藏。致密储层段孔喉结构复杂,呈低产低压特征;特殊岩性段白云石含量较高、脆性大,含油性及原油物性较好,利于储层压裂改造。虽然单个凹陷分布规模较小,但总体规模较大,资源预测结果表明,致密油资源量达到近10×10~8 t。在今后较长时间内,勘探工作应为致密油与岩性油藏并重。

Reservoirs in Erlian Basin are generally with low porosity and low permeability. Reservoir in the special lithologic section and tight glutenite segment in the trough area and tectonic wings under the top of K1btI and Klba is particularly dense with air permeability less than 0.5 mD. Two types of high-quality source rocks characteristic of special lithology containing a cloud of gray matter and clayey lacustrine mudstones developed under the top of K1 bt1 and K1 ba. Hydrocarbon source rock and tight reservoir are distributed as one or interbedded layers, which is favorable for hydrocarbon migration and accumulation. Tight reservoir has a complex pore structure, and is characteristic of low production and low pressure. With high dolomite content and brittleness, special lithologic reservoir is of good oil-bearing and physical properties, and is favorable for fracturing. Although a single depression is small in size, but the whole reservoir is of large scale. Predicted by oil and gas resources, tight oil resources amount is nearly one billion. The exploration work in the future should be focused on both tight oil and lithologic reservoirs.