论文部分内容阅读
声波测井结合中子测井或密度测井计算而得出的速度异常测井,是获悉井下碳酸盐岩地层中主要孔隙类型信息的一种工具,该测井所得信息可用来追踪(预测)井下成岩作用的分布情况及估计渗透率的变化趋势。对300个独立的碳酸盐岩样品进行实验分析发现,声波速度不仅和总孔隙度呈函数关系,而且可以反映主要的孔隙类型。一般孔隙度和速度呈负相关,但是对某种孔隙类型来讲,会出现比较大的偏差。在总孔隙相同的条件下,格架孔隙(如铸模孔、粒内孔)中,要比非刚性岩石格架中的孔隙(如粒间孔、微孔隙)中的声波速度大。实验室分析结果可用来精细解释标准电缆测井曲线,如本文中通过对大巴哈马滩上第三系碳酸盐岩地层两口井的研究。速度异常测井,是用时间平均方程把孔隙度测井数据转换成合成速度测井而求得。可用速度异常测井表示真实声波测井和合成声波测井之间的差异,因为异常是由于声波在孔隙度中传播速度发生变化引起,所以速度异常测井信息就能反映不同孔隙类型特征的不同岩石物理特征。正速度异常代表地层中速度高于从孔隙度值预测的值,如刚性格架孔隙占主导的地层;零异常代表地层缺乏刚性格架的地层,比如含大量粒间孔、微孔隙的碳酸盐岩地层;负异常则代表由孔洞型裸眼井壁、裂缝或自由气体含量高造成的声波测井速度很低的地层。通过连续追踪井下速度异常,可以识别出具不同孔隙类型特点的成岩相带。这种方法还可以用来观察渗透率变化规律,因为孔隙类型影响着岩石渗透率。
Sonic logging, combined with neutron or density logging computations, is a tool that learns the information on the major pore types in downhole carbonate formations, and the resulting information can be used to track (predict ) Underground diagenesis and the estimated trend of permeability change. An experimental analysis of 300 individual carbonate samples shows that the acoustic velocity is not only a function of the total porosity but also reflects the major pore types. Generally, porosity and velocity are negatively correlated, but for some pore types, large deviations will occur. Under the same total pore space, the lattice porosity (such as the mold hole and the intragranular hole) is larger than the acoustic velocity in the pores (such as intergranular pores and micropores) in the non-rigid rock framework. Laboratory analysis results can be used to finely interpret the standard cable logs, as described in this paper by studying two wells in the Tertiary Carbonate Formation on the Grand Bahamas. Logging of velocity anomalies is accomplished by converting porosity log data into composite velocity logs using a time-averaged equation. The available velocity anomaly logs represent the difference between true and synthetic sonic logs because anomalies are caused by changes in the velocity of the sound waves propagating in the porosity so that velocity anomaly log information can reflect differences in characteristics of different pore types Rock physical characteristics. Anomalous positive velocities mean that the velocity in the formation is higher than the value predicted from the porosity value, such as the strata in which the rigid framework pores predominate; zero anomalies represent the strata in which the strata lack a rigid framework, such as carbonates with numerous intergranular pores and micropores Salt rock formation; and negative anomalies represent strata with very low acoustic logging velocity caused by the high porosity, open fractures or free gas. By continuously tracking downhole velocity anomalies, diagenetic facies belts with different pore types can be identified. This method can also be used to observe the variation of permeability because the type of pores affects rock permeability.