碳同位素现场检测技术分析致密油气充注特征——以渤海湾盆地民丰洼陷北斜坡为例

研究油气充注对于寻找勘探目标和落实井位部署都十分重要。为此,以渤海湾盆地民丰洼陷北斜坡为例,选择盐斜233井、永斜932井及盐22井区开展现场碳同位素检测工作,并基于全新的碳同位素测量仪器在钻井现场获取的大量碳同位素数据,比对该区生产井天然气的碳同位素数据、组分数据,结合烃源岩演化、原油地球化学特征、储层沉积环境与物性特征,分析天然气在单井的充注特征和区域上的充注范围,探讨利用碳同位素现场检测手段来判识油气充注的可行性。研究结果表明:①盐斜233井沙四纯下亚段发生了深层油气的充注,天然气为深层原油裂解气与本地烃源岩热裂解气的混合气;②永斜932井沙三、四段天然气为本地烃源岩的热裂解气,但个别井段存在着深层天然气充注;③盐22井区油藏伴生气碳同位素值在该区中部重两侧轻、南重北轻,与储层物性分布特征一致,反映高成熟天然气的充注受储层物性控制;④盐22井区原油为本地烃源岩成熟阶段产物,而天然气则是在本地原油伴生气基础上存在着深层高成熟产物的充注。结论认为:①民丰洼陷北斜坡西北向存在着一个高成熟油气充注区,是有利的油气勘探目标;②碳同位素现场快速检测技术能够提供大量连续的立体碳同位素数据,可以快速分析油气充注特征、判断油气来源与成因,为油气开发部署提供参考。

Analysis of tight oil and gas charging characteristics by the carbon isotope field detection technology: A case study of the northern slope of the Minfeng sub-sag in the Bohai Bay Basin

Studying hydrocarbon charging is quite important for searching exploration targets and confirming well locations. In this paper, the north slope of the Minfeng sub-sag in the Bohai Bay Basin was taken as an example. The wells Yanxie 233, Yongxie 932 and Yan 22 were selected for on-site carbon isotope detection. Then, based on sufficient carbon isotope data which were acquired on the drilling site using the brand-new carbon isotopic measuring instrument, the carbon isotope data and composition data of natural gas produced in this area were compared. And combined with the evolution of source rocks, the geochemical characteristics of crude oil, the depositional environment of reservoirs and the physical properties, single-well charging characteristics and regional charging area of natural gas were analyzed. Finally, the feasibility of on-site carbon isotope detection method to discriminate hydrocarbon charging was discussed. And the following research results were obtained. First, deep hydrocarbon charging happened in the lower fourth Member of Shahejie Formation in Well Yanxie 233, and its natural gas is the mixture of the oil cracking gas of deep layers and the thermal cracking gas of autochthonous source rocks. Second, the natural gas in the third and fourth Members of Shahejie Formation in Well Yongxie 932 is the thermal cracking gas of autochthonous source rocks, but deep gas charging occurred in particular hole sections. Third, the carbon isotope of associated gas in Well block Yan 22 is high in the central area and low in both sides and high in the south and low in the north, which is accordant with the distribution characteristics of reservoir physical properties, indicating that the charging of high-maturity natural gas is under the control of reservoir physical properties. Fourth, the oil in Well block Yan 22 is the product of autochthonous source rocks in the mature stage while the natural gas is the autochthonous oil-associated gas combined with the charging of deep high-maturity product. It is concluded that there is a high-maturity hydrocarbon charging area in the northwest of the northern slope of the Minfeng sub-sag, and it is a favorable hydrocarbon exploration target. What’s more, the on-site carbon isotope rapid detection technology can provide a large number of continuous three-dimensional carbon isotope data, and it can be used to quickly analyze the characteristics of hydrocarbon charging and determine the source and origin of hydrocarbon, so as to provide reference for hydrocarbon development deployment.