济阳坳陷深层沙河街组四段轻质油—凝析气成藏条件

轻质油和凝析气是济阳坳陷古近系沙河街组四段（沙四段）深层勘探的重要目标，为明确其成藏条件，系统分析了其烃源岩特征、油气相态演化规律、油气藏流体特征、储层成岩作用、烃源岩排出酸性流体特征及其对储层成岩的影响。研究表明，济阳坳陷沙四段烃源岩为盐湖—咸化环境沉积，有机质类型为Ⅰ—Ⅱ₁型，生成油气相态演化分为4个阶段：常规油（含未熟—低熟稠油）阶段、轻质油阶段、凝析气阶段和湿气—干气阶段，其中，埋深4 100~4 800 m为轻质油和凝析气生成阶段，对应有机质的镜质体反射率为1.0%~1.7%。沙四段轻质油和凝析气为晚期成烃，上覆的区域性厚层状沙河街组三段烃源岩处于生烃阶段，轻质油和凝析气多赋存于源内和邻近储层中，其中，砂砾岩储层发育残余原生孔和次生孔，以次生溶蚀孔为主。深层轻质油和凝析气藏压力系数在0.95~1.98，以超压为主，油气藏温度多在157~175℃。沙四段烃源岩排出酸性流体分为4个阶段，早期排出的酸性流体和烃类进入储层时有利于原生孔隙的保存，而热硫酸盐还原的富H₂S、CO₂流体对深层储层次生孔隙形成具有重要作用。分析认为，济阳坳陷深层靠近深洼陷的沙四段烃源岩或其附近的砂砾岩体、沙四段烃源岩侧向及下伏潜山等是常规轻质油—凝析气藏的有利勘探目标，而陡坡带砂砾岩体的前缘或远端富含砂质条带的页岩是轻质页岩油的有利勘探目标。

Accumulation conditions for deep light oil and condensate gas from Member 4 of Shahejie Formation in Jiyang depression

Light oil and condensate gas are the important targets for deep exploration in Member 4 of Paleogene Shahejie Formation in Jiyang depression. In order to clarify the reservoiring conditions, this paper systematically analyzes the source rock features, oil-gas phase evolution law, oil-gas reservoir fluid characteristics, reservoir diagenesis, characteristics of acid fluid expelled from source rock and its influence on reservoir diagenesis. Research suggests that the source rocks from Member 4 of Shahejie Formation in Jiyang depression are sediments in salt lake-salty environment, and the organic matters are of type Ⅰ and Ⅱ₁. The oil-gas phase evolution expelled from the source rocks from Member 4 of Shahejie Formation can be divided into 4 stages corresponding to conventional oil (including immature-low mature heavy oil), light oil, condensate gas, as well as wet and dry gas, respectively. Light oil and condensate gas were generated at the buried depth of 4 100~4 800 m, and the corresponding vitrinite reflectance of organic matters ranges from 1.0% to 1.7%. The light oil and condensate gas from Member 4 of Shahejie Formation generated hydrocarbons in late stage. Since the overlying source rocks of Member 3 of Shahejie Formation were in the hydrocarbon generation stage, the light oil and condensate oil mostly occurred in intra-source and adjacent reservoirs. Residual primary and secondary pores are developed in glutenite reservoirs, which are dominated by secondary erosion pores. The pressure coefficient of deep light oil and condensate gas reservoirs ranges from 0.95 to 1.98, and the overpressure plays a dominant role. The temperature of oil and gas reservoirs is generally between 157℃ and 175℃. The acid fluids expelled from the source rocks of Member 4 of Shahejia Formation are divided into 4 stages; and the acid fluids and hydrocarbons expelled in early stage are conductive to the preservation of primary pores when entering the reservoirs, while the H₂S- and CO₂-rich fluids rich formed by thermal sulfate reduction play an important role in the formation of secondary pores in deep reservoirs. Therefore, the source rocks or adjacent glutenite from Member 4 of Shahejie Formation near deep sag in Jiyang depression and the lateral and underlying buried hills in the source rocks in Member 4 of Shahejie Formation are the favorable targets for the exploration of conventional light oil and condensate gas reservoirs, and the banded sandy shale at the front edge or far end of the glutenite in steep slope zone is the favorable target for the exploration of light shale oil.