深部流体对断层封闭性的影响—以惠民凹陷临南洼陷为例

Linnan subdepression in Huimin sag is characterized by fault block reservoirs in Mesozoic-Cenozoic, where the faults cutting through the sandstones have a good sealing ability in the high sand concentration stratum in the study area. Fault is an important passage of magma and deep fluid, which have an important effect on the diagenesis and the physical property of reservoir. The project centers around the micro mechanism of fault sealing and analyzes the mineral composition of fault zone filling, mineral existent condition, space-occupying relation; by the methods of carbon and oxygen isotope, inclusions temperature, strontium isotopes, sulfur isotope, and rare-earth elements, etc, and combined with the times of magma intrusion, fault activities, and the mineral assemblages relevant to hydrothermal solution activities, the mechanism of deep fluids' effect on fault sealing is discussed, and the origin of geological fluids is traced. According to the relationship between displacement pressure and physical properties and oil column height, the effect of reservoir physical properties on the sealing capacity from deep fluids is quantitatively evaluated. In addition,the interaction pattern between deep fluids affect and fault sealing is established, and the rules among log response characteristics, width of cemented zone, and distance from the section are summarized. Based on the log response characteristics,the filling state of fault zone and fault sealing property in unknown fault block can be deduced; therefore, this research will not only improve the accuracy of oil and gas exploration, but also enrich the mechanism of diagenesis with guiding significance and great implications for oil and gas exploration in this area and in the fault block reservoirs of eastern China.

惠民凹陷临南洼陷为中新生代典型的断块油气藏，该区高砂地比地层区块，存在断层封闭性依然较好的现象，断层作为岩浆活动的重要通道，岩浆和深部流体活动对其附近储层的成岩作用和物性具有重要影响。本项目围绕断层封堵的微观机理问题，分析断裂带充填物的矿物组成、赋存状态、占位关系，采用碳氧同位素、包裹体测温、锶同位素、硫同位素及稀土元素等技术，结合区域岩浆侵入期次、断裂活动和热液活动有关矿物组合等，探讨深部流体对断层封闭影响的机理，追踪地质流体的来源；根据排驱压力与物性、油柱高度关系，对深部流体对储层物性和断层封堵能力的影响进行定量评价；建立深部流体影响断层封闭性的作用模式，总结测井响应幅度与充填胶结带宽度、距断面距离关系的规律，根据测井响应特征推断未知断块的断裂带充填情况和断层的封闭性，提高油气勘探的准确度，丰富断层封堵的微观成岩机理，指导该区油气勘探开发，对我国东部断块油气藏的勘探开发具有借鉴作用。

我国东部地区中新生代盆地以发育断块油气藏为特征，断层的封堵能力是油气成藏的关键因素之一。惠民凹陷临南洼陷断层发育，构造破碎，为典型的断块油气藏。研究区勘探程度较高，勘探开发中发现该区高砂地比情况下，砂岩大量对接，但断层封堵性仍然较好。通过取心井铸体薄片、扫描电镜、粘土矿物、全岩矿物、碳酸盐含量、同位素分析以及孔隙度、渗透率和压汞等测试，分析成岩作用对断层封堵的影响，以解释高砂地比情况下断层的封堵性。不同期次的深部流体，影响到沉积盆地尤其是断层附近的成岩作用。深部流体富含CO2、CO、H2、K+、Na+、卤素等，其中的K+、Mg2 +的存在使碎屑岩、泥岩发生广泛的伊利石化、绿泥石化等；在CO2流体参与下，碳酸盐岩发生白云岩化、铁白云岩化。深部流体引起以上对温度变化敏感的砂岩填系物的重新分配，大大降低了储层的物性，增加了断层的封堵能力。在综合考虑断层带泥岩含量、区域应力、流体压力、断面产状等因素影响的基础上，提出断层封闭系数和断层封闭性模糊评价方法对断层封堵能力进行评价。根据研究区大量实测数据分别回归出排驱压力与油柱高度、SGR、孔喉半径以及与孔隙度和渗透率的关系；泥岩含量与排驱压力之间呈正相关的关系，孔喉半径与排驱压力呈负相关关系，孔隙度和渗透率与排驱压力之间呈负相关性。可提高油气勘探的准确度，丰富断层封堵的微观成岩机理，指导该区油气勘探开发，对我国东部断块油气藏的勘探开发具有借鉴作用。