北海盆地大油气田形成条件及分布特征

Formation and Distribution of Giant Oil and Gas Fields in North Sea Basin

北海盆地为典型的中生代裂谷盆地,其油气的形成与分布具有较明显的特征,了解它们的形成与分布可以指导其他裂谷型盆地的勘探。根据IHS及C&C提供的相关数据,结合生油层、储层、盖层及圈闭特征方面的研究,对北海盆地及邻区已发现的57个大油气田进行分析,得出南北海盆地气源岩为上石炭统威斯特伐利亚阶煤系地层,北北海盆地主要油源岩为上侏罗统到下白垩统沉积的KimmeridgeClay组(英国)、Mandal组、Draupne组(挪威)和Farsund组(丹麦)泥页岩;主力储层分别为南北海盆地的赤底统砂岩,北北海盆地维京地堑内中侏罗统Brent群砂岩及中央地堑内的上白垩统白垩;南部区域盖层为上二叠统盐岩,北部区域盖层以泥灰岩为主。北海大油气田形成与分布的主要受控因素为:有效烃源岩分布及其成熟度;优质储集体的发育及其分布;盐运动及同裂谷期断裂作用产生的相关盐构造和断块背斜、掀斜断块圈闭的发育;区域性盐岩及泥灰岩盖层的有效封盖。这些有利条件共同作用下,北海大油气田在整个区域上具南部产气、北部以油为主的特点;局部上,受有利储层Brent群分布位置和中央地堑区域盐构造运动影响,大油田集中富集于维京地堑西北部与中央地堑中部挪威区域。

North Sea Basin is a typical Mesozoic rift basin, of which the formation and distribution of oil and gas has obvious characteristics. To understand the oil and gas formation and distribution could guide the exploration of other rift basins. Based on the relevant data provided by C&C and IHS, combined with the generation, reservoir, cap rock and trap features research, this paper analyzes the 57 giant oil and gas fields found in the North Sea Basin and adjacent areas, and concludes that the gas source rock of southern North Sea Basin is Westphalian coal of Upper Carboniferous, the main oil source rock of northern North Sea Basin is the shales of Kimmeridge Clay (Britain), Mandal, Draupne (Norway) and Farsund (Denmark) Formations from Upper Jurassic to Lower Cretaceous; the main reservoir of southern North Sea Basin is Rotliegendes sandstones, the Middle Jurassic Brent Group sandstones in Viking Graben and Upper Cretaceous chalk in Central Graben to the north; the regional cap rock of southern North Sea Basin is halite, and mud limestone to the north. It is also found that the critical factors that control the formation and distribution of giant oil and gas fields are: the distribution and maturity of effective source rock, the development of good reservoir rock and its distribution, the development of halite tectonic, fault block anticline and tilted fault block trap induced by halite and faulting movement during syn-rift period, the effective sealing by regional halite and mud limestone. Owing to these beneficial factors, the North Sea Basin is generally characterized by gas generation in the south and mainly oil generation in the north. Locally, because of the distribution of Brent group, and structural movement of regional halite in Central Graben, most giant oil and gas fields concentrate in northwestern Viking Graben and Norway area in middle of Central Graben.