摘要
惠民凹陷西南斜坡是一长期发育的稳定斜坡,其上发育不同产状的基底断层,构成复杂的断块构造。早第三纪断陷阶段,断裂强烈活动,对沙河街组沉积有明显的控制作用。晚第三纪、第四纪,大多数断裂均停止了活动。运用泥涂抹系数,对夏口断层封闭性进行研究,结果表明,以夏口断层的沙河街组三段中亚段为界,之上封闭性好,之下封闭性差。这一特征决定了临南洼陷沙河街组三段中亚段以上层位的油气无法穿过夏口断层,只能在断层上盘形成聚集;以下层位的油气却能穿过夏口断层,进入到西南斜坡。因此,西南斜坡的油气勘探重点应放在沙河街组四段及以下层位
Abstract
The southwest gentle slope belt in Huimin sag is located in the structural slope to the south of Xiakou fault. In the north,it is adjacent to Linnan depression, an important oil kitchen,and is bounded by Xiakou fault zone; it is adjacent to Luxi uplift in the south, Qudi horst and Jiyang graben in the east, and Yucheng depression in the west. Its area is about 500 km. The Paleogene in the gentle slope belt is relatively thin. On the whole, it appears to be a wide and gentle monocline,uplifted in the south and dipping to the north.There are only a few NNE conjugated normal faults with small displacement in it. At the same time, these faults cut through the strata into the basement and pinch out upward in the Paleogene or end up beneath the unconformity.The Cenozoic tectonic evolution in that area can be divided into 4 stages:(1)During the deposition of Kongdian Fm to E,Huimin sag was a simple half-graben fault depression and the southwest gentle slope belt was located on the structural slope of the half-graben. The tilting movement resulted in the whole area to be dipping to the north,and so deposited a wedge-shaped sedimentary sequence composed of Kongdian Fm -E. During this stage, the displacement of Xiakou fault was small,and it could be regarded as accommodating the counter-inclined fault developed on the hanging wall of Linshang fault. (2)During the deposition of E-E,the activity of Xiakou fault was intensive,which became the southern boundary fault of the graben-type Linnan depression. The southwest gentle slope belt located on the footwall of Xiakou fault subsided slowly,and the tilting had apparently been restrained. There were conjugated normal faults with small displacement in the belt. The thickness of the E and E were relatively thin and uniform. (3)During the deposition of E to Dongying Fm,the faults in the southwest gentle slop belt had stronger activity. During the depositon of the Dongying Fm,the tilting made the whole belt to be dipping to the north .(4)During the deposition of the Neogene to Quaternary, Xiakou fault and the faults within the southwest gentle slope belt were basically inactive. As a result, a regional unconformity occurred between Guantao Fm and the underlying formations. In the southwest gentle slope belt near the basin margin,source rock can only be found locally in some well-developed E. The sealing characteristics of Xiakou fault have an important effect on the hydrocarbon migration and accumulation in the southwest gentle slope belt. Xiakou fault is characterized by listric and high-angle plane fault. The smearing coefficient analysis of Xiakou fault indicate that the fault's sealing property becomes poorer with increasing depth. The middle E and younger formations have relatively good sealing characteristics, while the lower E, E and older formation have relatively poor sealing characteristics. The E source rock in the southwest gentle slope belt reached the hydrocarbon-generating threshold (2 600 m) after Dongying Fm was deposited. The hydrocarbon generated from E source rock on the hanging wall of Xiakou fault can migrate laterally through the fault to the southwest gentle slope belt. Because of the lack of source rock in E and sequences above it, and the sealing of Xiakou fault, the hydrocarbon generated in Linnan depression have been hampered to migrate to the gentle slope belt. The characteristics of the structural evolution and the hydrocarbon accumulation model set up from the migration condition show that fault-block and stratigraphic traps might be formed in the E and older formations in the southwest gentle slop belt,but oil and gas reservoirs would hardly be formed in the E and younger formations.
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