川西北深层中二叠统茅口组岩相古地理及勘探意义

The Lithofacies Paleogeographic of the Middle Permian Deep Maokou Formation and Its Significance for Hydrocarbon Exploration, Northwestern Sichuan Basin

四川盆地西北部是深层油气勘探的重点区域,围绕“开江-梁平海槽”发现多个长兴组台缘礁滩型气田.近年,随着该油气带下的茅口组获得新的油气发现,海槽的形成时间和范围及其对茅口组有利勘探区带的约束成为新的研究热点.基于川西北地区剖面钻井资料,详细开展茅口组的岩相古地理重建.揭示出川西北地区茅口中-晚期呈现深水相和台地相的分异,相带沉积作用造成地层厚度的带状协同差异;重建了茅口中-晚期的岩相古地理,刻画出该时期的构造-沉积分异格局;明确“开江-梁平海槽”形成时间应向前推至中二叠世晚期.总体上,茅口组深水槽沿广元-巴中-平昌一带展布,其两侧台缘是新的潜在大型油气聚集带.沿该深水槽的构造-沉积分异形成的台缘带为初始地貌继承型边缘,具有宽边缘、薄滩体的特点,滩相结构为间断加积状,与其上长兴期镶边塑造的连续加积或进积形成的窄边缘、厚滩体模式形成鲜明对比.

The northwest of Sichuan Basin are the key region of deep oil and gas exploration. Changxing Formation Formation platform marginal reef-flat gas fields have been discovered around "Kaijiang-Liangping" deep-water trough. Recently, with the new discovery of oil and gas in the Maokou Formation under the oil and gas accumulation zone, the forming time and scope of the deepwater trough and its constraint on the favorable exploration zone of the Maokou Formation have become a new research hotspot.Based on several field outcrop sections and drilling data in northwest Sichuan Basin, we reconstructed lithofacies paleogeographic of Maokou Formation in detail, and revealed the differentiation of deep-water facies and platform facies in Middle-Late of Maokou Formation. The sedimentation in facies belt results in the zonal synergistic difference in strata thickness;We reconstructed the lithofacies paleogeography and described the structure-sedimentary differentiation model of the Middle-Late Maokou Formation.This study confirms that the forming time of Kaijiang-Liangping trough should be pushed forward to the late of Middle Permian.Generally speaking, the deep-water trough of Makou Formation spreads along the Guangyuan-Bazhong-Pingchang area, and the platform margins on both sides are the potential development area of a new large-scale oil and gas accumulation zone. The platform margin zone formed by the tectonic-sedimentary differentiation is the initial geomorphological inherited margin along deep water trough, with the characteristics of wide margin and thin shoal body. The structure of shoal facies is discontinuous accretion, which is in sharp contrast to the narrow margin and thick shoal pattern formed by continuous accretion or progradation of generated on the edge in Changxing Formation.