推覆构造的特征及其与油气的关系

推覆构造是地壳中广泛发育的一种构造型式。逆冲断层常成带地平行排列,形成逆冲带和叠瓦构造。断层多呈上陡下缓或阶梯状,底部常有滑脱构造,并在深处常收敛在一个基底逆冲断层上。推覆构造还常与飞来峰、构造窗、叠瓦构造、牵引褶皱、后冲断层和平移断层等构造现象一起产出。推覆构造不仅扩大了找油的领域,它本身对油气的生成、储集、运移、圈闭和保存条件都有着重要的影响。虽然它们有时可造成某些对油气藏不利的因素,但更经常地则是造成油气藏形成的有利条件。当然,影响油气藏形成的因素十分广泛,它不仅限于推覆构造本身的某些特征,同时还决定于许多其它地质条件。因此,不同推覆构造或同一推覆构造的不同部位,其含油气远景也是很不相同的。

NAPPE TECTONIC FEATURES AND THEIR RELATIONSHIP TO OIL AND GAS ACCUMUIATIONS

Nappe tectonics and thrust faults are a type of structural form widely developed in the earth's crust.Thrust faults are often arranged in parallel,zonal belts forming imbricate structures. Most of these thrusts faults are relatively steeply dipped in the shallow depths and gently dipped in the lower depths which are often stepped, Decollement structures often exist at the base of these thrust and numerous thrust faults often converge into a single thrust fault at great depths.Nappe tectonics are often accompanied with klippes, fensters, imbricate stuctures, decollement structures, drag folds, back thrusts, strike-slip faults and other structural features.Nappe tectonics are not only important in oil and gas explor-ation but also greatly influence the source rocks, reservoir rocks, cap rock, structural traps, oil and gas migration and preservation. These structural features often play a favourable role in the formation of oil and gas accumulations. However, these same structural features may be unfavourable in certain situations.It is noted that the influencing factors in the formation of oil and gas accumulations are very extensive and not solely related to structural characteristics of thrust fault systems. many other geological and geochemical conditions are also important in oil and gas development and accumulation.Strictly speaking, conditions vary greatly from one thrust fault system to another and vary within single thrust fault systems making the potential for oil and gas development and accumulation unique to each area.