圈闭含油气概率赋值标准及其在塔里木盆地的应用

Assignment standard for hydrocarbon-bearing probability of traps and its application in Tarim Basin

圈闭含油气概率赋值标准是圈闭含油气性量化评价的基础,是勘探风险分析的重要内容。从圈闭成藏的地质过程出发,鉴于圈闭、充注、储集和保存4项成藏条件相互独立、缺一不可,因此采用这4项成藏条件作为主因子,并用其各自概率的乘积表示圈闭的含油气概率。对于纵向上由多个目的层组成的圈闭,其含油气概率是指至少有一个层圈闭发现油气的概率。在不同类型油气藏成藏主控因素及不同地区风险关键因素分析的基础上,进一步细化4项主因子,分别提出了存在和有效两类子因子。根据木桶短板效应原理,提出若各子因子关键参数独立,则其关键参数发生概率相乘即为圈闭含油气概率;若子因子关键参数相关,则取风险最大者与其他子因子概率相乘表示圈闭的含油气概率。同时,根据资料的相关程度、丰富程度、控制程度和质量评价,建立了概率赋值原则以及4项主因子及其子因子概率赋值标准,并将含油气概率分为5级。圈闭的含油气概率越大,地质风险越低;反之亦然。该方法在塔里木盆地实际应用,取得较好效果。

Assignment standard for hydrocarbon-bearing probability of traps is the basis of quantitative assessment hydro-carbon potential of traps and has played a very important role in exploration risk analyses .Four key reservoiring elements including trap ,charging ,reservoir and preservation were chosen to be the major factors to represent hydrocarbon-bearing probabilities of traps with the products of their individual probabilities .For traps composed vertically of several target re-servoirs,the hydrocarbon-bearing probability refers to the probability of founding oil or gas in at least one target reservoir of the trap.Each of the four factors was further divided into two subfactors-occurrence subfactor and effective subfactor-based on different reservoiring controlling mechanisms and risk analyses of various oil or gas reservoirs .By applying the Barrel Effect principle to our calculation ,we proposed that if all the key parameters of the subfactors were independent from one another ,then the hydrocarbon-bearing probability would be the product of probability of key parameters;on the other hand,if the subfactors were related to one another ,then the probability would be the product of probability of key parameter with the maximum risk multiplying that of other subfactors .Based on the relevance ,availability ,controlling le-vel and quality of data ,we established the principle for probability assignment and set up standards for assigning the proba -bilities to the factors and subfactors and a 5-level hydrocarbon-bearing probability system .According to the system , the bigger the probability of trap contains hydrocarbon ,the lower the geological risks ,and vice versa.Implementation of the method in Tarim basin has been proven positive .