秘鲁Ucayali盆地石油地质特征与油气成藏

Geological Characteristics and Hydrocarbon Accumulation of Ucayali Basin,Peru

基于对Ucayali盆地油气成藏要素的系统解剖,预测盆地内除已发现的逆冲背斜/断背斜外,还可能发育伸展断块、潜山、生物礁、地层尖灭、河道砂及逆冲断层下盘构造等多种圈闭类型,自西向东前展式推覆的逆冲背斜/断背斜为最主要的圈闭类型。前陆运动前盆地构造圈闭发育程度低,现今原油聚集多属前陆运动后二次调整成藏,淡水侵入使浅部油藏普遍遭受轻度降解。由于Shira隆起的分隔作用,西部次盆现今生成的烃类很难运移至东部圈闭中。而东部次盆烃源岩埋深小,Ene组展布面积有限,Ambo群趋于生气,在生油窗内生成的液态烃类相对有限,加之圈闭不断生长,圈闭充满度较低。同时,活动性断层对烃类侧向运移不利,其东侧的背斜圈闭往往无法得到有效充注,形成大规模原油聚集的潜力较小。南部和西部次盆成藏条件配置好,逆冲褶皱发育,圈闭可得到烃类持续充注,主要以天然气为主;南部次盆逆冲断层下盘构造圈闭为重要潜在勘探目标;Ene次盆勘探程度低,烃源岩品质好,仍有发现大型构造圈闭的潜力。

Based on the geological and hydrocarbon accumulation characteristics,there will be other types of hydrocarbon traps in Ucayali basin,such as extensional fault block,buried hill,reef,stratigraphic pinchout,channel sand and the footwall of thrust fault,besides the discovered thrust anticline / faulted anticline oil gas fields. The in- sequence thrust anticline / faulted anticline will be the main traps. The traps were not well developed before the foreland orogeny,and the current hydrocarbon accumulations were mostly the product ofsecondary migration. The intrusion of freshwater mildly degraded most of oil in shallow reservoirs. Due to the separation of the Shira uplift,it was difficult for the hydrocarbon generating in the Western Sub basin to migrate into the Eastern Sub basin. The source rocks in the Eastern Sub basin was not buried deeply enough,the Ene Formation had limited distribution,the Ambo Group was gas prone,only limited liquid were generated in oil window,and the traps were growing,so the filling of traps were generally low. The active faults also are barriers for hydrocarbon parallel migration,the traps in the eastern side often have charge risk,and have little chance to form large oil accumulation. The Southern and Western Sub basins had good conditions for hydrocarbon accumulation,the thrust folds were well developed,the traps were continuously charging,and most likely to form gas fields. The foot wall anticlines of thrust faults will be the potential targets in Southern Sub basin. The Ene Sub basin is in low degree of exploration,and with perfect source rocks,so it has the potential to find large structural traps.