河北霸县凹陷兴隆宫地区沙三段岩性油气藏成藏条件与圈闭模式

Stratigraphic Hydrocarbon Reservoir's Accumulation Elements and Trap Models in 3^(rd) Member of Shahejie Formation in Xinglonggong Area,Baxian Depression,Hebei

裂谷型凹陷深层的油气勘探前景一直为众多学者所关注。兴隆宫地区紧临霸县生油洼槽,其沙三段埋深较大,勘探程度较低,少量探井证实这一些地区的沙三段具良好的油气成藏前景。应用石油地质学中的油气成藏理论,系统论述该区有利的岩性油气藏成藏条件与圈闭模式:沙三段圈闭接近沙四段、沙三段及沙一段的油源,具有优越的油气源条件;沙三段大型三角洲前缘与浊积扇等储层条件较好;沙三段同沉积构造与坡折带利于岩性油气藏形成;膏泥岩、盐岩及泥岩提供盖层与保存条件。而该区沙三段岩性油气藏成藏的圈闭模式可分为3个区带:陡坡带主要发育构造—岩性圈闭、小型三角洲前缘砂岩岩性圈闭;缓坡带以大型三角洲前缘砂岩岩性圈闭、地层超覆、地层不整合圈闭为主;而洼槽带以坡折附近的尖灭砂体圈闭为主。陡坡坡折之下发育扇三角洲前缘与浊积扇圈闭;缓坡坡折之下发育与低位三角洲、浊积扇及滩坝砂体有关的岩性圈闭。通过研究可以确定东部文安缓坡坡折带以下地区是目前岩性油气藏的最有利勘探区带。

The petroleum exploration prospective of deep strata in rift depression is always concerned by lots of geologists. Xinglonggong area, closely adjacent to Baxian depression which is the petroleum generation depression, has many advantageous hydrocarbon accumulation conditions. In this area, some industrial petroleum traps were searched in Dongying Formation and 1^st Member of Shahejie Formation. The petroleum exploration degree of this area was much lower than those of other places in 34 Member of Shahejie Formation, which was the deep strata in the Baxian depression, although a few exploration wells confirmed that there were some favorable elements to hydrocarbon＇s accumulation, especially, to the stratigraphic reservoirs. According to hydrocarbon accumulation theory of petroleum geology, the favorable conditions of stratigraphic hydrocarbon accumulation and trap models discussed in this paper are as follows： Firstly, the hydrocarbon sources are sufficient because the traps of the 3^rd Member of Shahejie Formation are close to source rocks which are shales from the 4^th, 3^rd and 1^st members of Shahejie Formation; Secondly, the reservoir conditions are very good owing to the sandbodies of large scale delta front and some turbidity deposition; Thirdly, oil accumulation of stratigraphic reservoir benefits from the slope breaks and synsedimentary structures; Finally, the gypsum, gypsum shales, shaly gypsum, halites and shales can act as caprocks. According to the structure area dividing, three area-models of strafigraphic petroleum trap are summarized： abrupt slope, gentle slope and depression models. In abrupt slope area, structure-stratigraphy-trap and small scale delta front sandbodies developed. In gentle slope area, hydrocarbon is prone to accumulate in large scale delta front, overlapping strata and some sandbodies adjacent to unconformity. However, in the depression area, pinched out sandbodies are typical, i. e. , below the break areas of abrupt slope, fan delta front reservoirs and turbidity sandbodies are favorable petroleum traps, and under those areas of gentle slope, delta front reservoirs, turbidity sandbodies and sheet sand bars are the places for hydrocarbon accumulation in the low system tract. According to the studies of petroleum accumulation elements and trap models, those areas below the break point of Wen＇an gentle slope in the east part of Xinglonggong area are considered to be the most profitable place for hydrocarbon exploration.