渤海湾盆地歧口凹陷沙河街组天然气赋存状态及其勘探意义

Occurrences of the Natural Gas in Shahejie Formation of Qikou Depression in Bohai Bay Basin and Its Exploration Significance

近年来,随着歧口凹陷深层油气的勘探,在深层(>3 500m)沙河街组发现了大量的天然气藏,这些天然气藏主要沿深大断裂分布,垂向上具有下气上油、浅层为气的分布特征。为了解天然气在油水中的赋存状态,指导油气勘探,依据天然气各组分在油水中的溶解性的影响因素(温度、压力、油密度、水矿化度等),计算出地层条件下天然气在原油和水中的溶解量,并与实际油气产量进行了对比分析。沙河街组天然气在油水中大多数达到饱和—过饱和,垂向上形成了深层游离气为主,向中深层逐渐过渡为油溶气及少量的游离气,临近沟通气源的深大断裂浅层因气源充足可形成游离气。据此探讨了研究区内油气运聚成藏模式,认为沟通油气源的深大断裂浅层是寻找凝析气藏和纯气藏的有利区域,中深层因生油窗内有大量原油的存在是寻找油藏、油溶气藏或轻质油藏的有利靶区,深层断裂相伴生的圈闭有利于凝析气藏及纯气藏的富集。

Abundant natural gas reservoirs with burial depth 〉3 500 m have been found recently in the Shahejie Formation of the Qikou Depression. The natural gas reservoirs were distributed linearly along the faults and were featured by hybrid gas-oil-water relationships, which were widely recognized in unconventional hydrocarbon reservoirs. In order to understand the occurrence of natural gas in geological conditions for guiding further exploration,this paper calculated the content of gas component dissolved in the crude oil and formation water, affected by temperature, pressure, crude oil property, water salinity, and then compared with the oil production and natural gas output. Most natural gases of Shahejie reservoirs dissolved in the oil and water have been saturated to supersaturation, which formed the hybrid gas-oil-water relationship of free gas in deep transition to shallow of dissolved gas in oil reservoirs or a small amount of free gas, and those reservoirs linearly along those fault which connect with the gas source can be rich in free gas. Meanwhile, the paper discussed the pattern of the oil and gas migration and accumulation after analysis of the occurrences of the natural gas and the distribution of the gas and oil reservoirs. The areas in shallow linearly along those deep faults connecting oil and gas source are benefit to search of condensate gas reservoirs or pure gas reservoirs,in the middle-deep layers for the existence of oil-generating window with the huge quantities of crude oil being better to look for oil reservoirs or dissolved gas-oil reservoirs or light oil reservoirs, and in deep the concomitant fracture traps are easy to enrich the free gas and form the condensate gas reservoirs and the pure gas reservoirs.