鄂尔多斯盆地延长组低渗透致密岩性油藏成藏机理

摘要

By analyzing the hydrocarbon accumulation conditions under the guideline of sequence stratigraphy, the hydrocarbon accumulation mechanism in the low permeability, tight reservoirs of the Yanchang Formation in the Ordos Basin is studied from the perspective of pore evolution, and the hydrocarbon accumulation evolution models are concluded. The low permeability, tight reservoirs of the Yanchang Formation are distributed within the range of good hydrocarbon source rocks. The reservoir sand-bodies are dominated by lacustrine gravity flow deposits and delta front deposits. In the early period when hydrocarbons are accumulated in the Yanchang Formation, the reservoirs are characterized by high porosity and high permeability. The oil and gas generated in the period are accumulated normally under the effect of buoyancy. In the middle-late period, the reservoirs have experienced continuous compression. The petroleum generated in the late period, the major hydrocarbon generation period, migrates and accumulates by infiltration along the previously remained paths under the effect of buoyancy and pressure difference between the source rocks and the reservoirs. When the reservoirs become tight, oil and gas stop migration. From the Late Jurassic to the middle period of the Early Cretaceous, oil and gas widely charge the high porosity sandstones near the source rocks when they migrate from the center of the lacustrine basin to me borders. In the late period of the Early Cretaceous, the diagenesis of sandstone reservoirs is enhanced, making the reservoirs tight. After the Late Cretaceous, the present low permeability tight lithologic reservoirs are formed due to the compressing and uplifing movement of the structure which dips down in the west and tilts up in the east.%以层序地层学为指导,从成藏条件解剖入手,从孔隙演化的角度分析鄂尔多斯盆地中生界上三叠统延长组低渗透致密岩性油藏成藏机理,归纳其成藏演化模式.延长组低渗透致密岩性油藏分布于优质烃源岩范围内,湖相重力流沉积与三角洲前缘沉积为主要储集砂体类型.延长组低渗透致密砂岩在早期成藏期具有高孔高渗的特点,早期生成的油气在浮力作用下正常成藏,中后期成藏过程中经历了持续压实致密过程；后期主生烃期生成的原油在浮力和源储压差共同作用下沿先前残余路径以浸润方式运聚,达到致密条件时,油气停止运移.晚侏罗世一早白垩世中期,油气在高孔隙砂岩中近源多点面状充注大面积成藏,油气从湖盆中心向四周运移:早白垩世晚期,砂岩储集层成岩作用加强,储集层发生致密化.晚白垩世之后,受西倾东翘的构造挤压抬升运动影响,形成现今低渗透致密岩性油藏.