歧口凹陷沙河街组成岩史分析和成岩阶段预测

DIAGENETIC HISTORY AND DIAGENETIC STAGES’PREDICTION OF SHAHEJIE FORMATION IN THE QIKOU SAG

渤海湾盆地歧口凹陷超压对有机质热演化、有机酸生成和水岩反应具有明显的抑制作用。在化学动力学模型中加入超压因子增加反应活化能,即可用于超压条件下有机质热演化和成岩作用的模拟。歧口凹陷深层(>3500m)主要为沙河街组(始新—渐新世)。在沙河街组沉积末期沙河街组三段(沙三段)就进入晚成岩阶段A1期,烃源岩开始生烃,生、储、盖层发育史与圈闭发育史匹配良好,油气藏开始形成。在东营组沉积时期(渐新世)—新近纪,沙河街组大部分地层处于晚成岩阶段A1—A2期,是其主要成藏期。现今沙河街组一段、二段和三段的上部仍处于晚成岩阶段A1—A2期,有利于油气藏的形成。然而,沙三段的下部在歧口凹陷的北部地区已进入晚成岩阶段BC期,镜质组反射率Ro≥1.3%,烃源岩处于高过成熟阶段,储层物性较差,不利于成藏,但在南部地区的沙三段下部还处于晚成岩阶段A1-A2期,生、储、盖层发育,是油气聚集的有利地区。

The organic matter maturation, organic acid generation and water-rock reaction were retarded by overpressure in the Qikou Sag of the Bohaiwan Basin. with higher active energy enhanced by overpressure factors could The chemical kinetic models be used for modeling the organic matter maturation and diagenetic history in a condition of the overpressured formation. As the diagenetic modeling results of deep horizons, composed of the Shahejie Formation （E2-3s） and the Dongying Formation （E3d） which were buried at a depth more than 3 500m, it showed that the Member 3 of Shahejie Formation （ E2-3s^3 ） entered the late diagenetic stage of A1 by the end of depositional period of the formation, the source rocks began to generate petroleum, the reservoir rocks developed secondary porosity, the cap rocks sealed oil and gas from escaping from traps, and the oil and gas pools formed from that time. During sedimentary period of the Dongying Formation and the Neogene, the deep horizons were located in the late diagenetic stages of A1-A2, the source rocks, reservoir rocks and cap rocks developed well, and the oil and gas pools formed in a wide scale. At present, the Members 1 and 2 of Shahejie Formation（ E2-3s^1 and E2-3s^2）and upper part of the Member 3 （ E2-3s^3-2 ） were still located in the late diagenetic stages of A1-A2 , but the lower part of the Member 3 （ E2-3s^3-4 ） , with overmatured source rocks and lower porosity reservoir rocks, got into the late diagenetic stages of B-C in the northern Qikou Sag, where the Ro=1.3% so as to be not favorable for petroleum ac- cumulation. The favorable region of E2s^3 for petroleum accumulation was situated in the southern Qikou Sag where E2s^3 was in the late diagenetic stages of A1-A2.