塔西南前陆冲断带油气成藏地质条件的分段性

Segmentation characteristics of geological conditions for reservoir forming in the foreland fold-thrust zone of the southwest Tarim basin

塔西南前陆冲断带成藏的地质条件具有分段性,即不同构造段成藏条件明显不同。成藏最有利部位是甫沙—克里阳、苏盖特—齐姆根两个构造带,发育了断层传播褶皱及三角带构造,集中了中—下寒武统碳酸盐岩、下石炭统—下二叠统及侏罗系暗色泥岩三套优质烃源岩,拥有下白垩统砂岩储层与古近系膏盐盖层、古近系碳酸盐岩储层与其上覆泥岩盖层、中新统砂岩储层与其中泥岩盖层以及上古生界等一系列优质储盖组合;其次为和田逆冲推覆构造带,准原地系统(原地系统)构造圈闭良好,但烃源条件和储盖条件相对较差,下二叠统克孜里奇曼(P1k)碳酸盐岩烃源岩达到气源岩的标准,下二叠统碳酸盐岩及砂岩储层、下奥陶统碳酸盐岩储层基本上都属低孔低渗型,下二叠统普司格组泥岩属优质区域性盖层;帕米尔前缘冲断带对成藏不太有利,虽有较好的生储盖组合,但发育大型推覆构造及强显露型冲断层,缺乏良好的构造圈闭。

The geological conditions for reservoir forming show the characteristic of segmentation in the loreland fold-thrust zone of the southwest Tarim basin, that is, different tectonic section has quite different reservoir forming conditions. Most favorable locations are the Pusha-Keliyang zone and the Sugaite-Qimugen zone, where developed many fault-propagation folds, triangle-zone structures and three sets of high-quality source rock including from the early to middle Cambrian carbonate source rock, from the early-Carboniferous to earlyPermian and Jurassic dark mudstone source rock, and also developed a series of better reservoir-cap assemblages such as the early-Cretaceous sandstone reservoir matching the Paleogene cap rock, the Paleocene carbonate reservoir matching its mudstone cap rock, and the Miocene sandstone reservoir matching its mudstone cap rock. The secondary favorable location is the Hetian thrust nappe where there are some good tectonic traps in- cluding irrsitu system and par-autochthonous system, but the source rock and reservoir-cap matching is a little worse. The early-Permian carbonate gas-source-rock reaches the criterion of a gas-source-rock; the early-Permian sandstone and the carbonate reservoirs, and the early-Ordovician carbonate reservoirs are all low porous and low per- meable; but the early-Permian mudstone is a set of regional good-qualky cap rocks. Finally, the Parnirs thrust zone may be not favorable for reservoir forming, owing to its large-scale nappe and thrust fault which result in the lack of good tectonic traps, although there are some advantageous source-reservoir-cap combinations.