海拉尔盆地牧原凹陷油气勘探前景与有利区带目标优选

牧原凹陷是海拉尔盆地群中研究程度和勘探程度均较低的凹陷,尚未取得勘探突破。为明确牧原凹陷的油气资源潜力与勘探前景,开展了野外地质调查、老井复查与烃源岩有机地球化学特征研究等,基本明确了凹陷油气地质条件: ①牧原凹陷具有单断箕状结构,可划分为陡坡带、洼槽带和缓坡带3个构造单元; ②发育大磨拐河组、南屯组和兴安岭群3套有效烃源岩,南屯组、大磨拐河组烃源岩厚度大,分布面积广,有机质类型好,以II₁-I型为主,有机质丰度高,生烃潜量大,热演化进入成熟阶段,是凹陷主力烃源岩,兴安岭群烃源岩有机质丰度高,处于高成熟阶段,虽然厚度与分布有限,也是一套有价值的烃源岩; ③发育兴安岭群的自生自储或上生下储、大磨拐河组与南屯组的自生自储、伊敏组的下生上储3套储盖组合。对比高勘探程度区单断箕状凹陷的成藏规律,结合牧原凹陷自身的地质特点,构建了牧原凹陷油气成藏模式。通过开展区带的初步评价,优选出2个有利区带,提出了勘探目标。

Petroleum exploration prospects and favorable zone evaluation in Muyuan sag of Hailaer Basin

Muyuan sag, with low exploration and research degree, has no great progress in petroleum exploration. Therefore, field geological survey, re-examination on old wells and organic geochemistry work were performed to investigate the oil and gas potential and exploration prospects. The petroleum geological condition was analyzed: ①Muyuan sag has dustpan-like feature with single fault and the sag consists of three structure zones—abrupt slope zone, deep sag zone and gentle gradient zone. ②Three effective source rocks, Damoguaihe Formation, Nantun Formation and Xing’anling Group, were developed. Nantun Formation and Damoguaihe Formation deposited thickly, distributed widely and maturated well with good organic type (II₁-I). These two formations also have high organic abundance, superior hydrocarbon generation potential with mature thermal evolution and they are major source rocks in the basin. Xing’ anling Group has high organic abundance and are in high-over maturity, with limited thickness and distribution, but it is still valuable source rocks. ③There exist three source-reservoir-cap rock associations in the basin, which are the self-source and self-reservoir or the upper-source and lower-reservoir type of Xing’ anling Group, the self-source and self-reservoir type of Nantun Formation and Damoguaihe Formation, the lower-source and upper-reservoir type of Yimin Formation. Compared with the reservoir formation law of dustpan-like feature with single fault in high-exploration area, combined with the geological characters in Muyuan sag, the hydrocarbon accumulation pattern was established. Based on the primary play assessment, two favorable exploration areas and targets were proposed.