基于辫状河露头剖面的变差函数分析与模拟

Variogram analysis and simulation on sedimentary outcrop profile of braided river

利用露头剖面资料丰富、取样点多、精度高、直观可靠等特点，建立研究区辫状河沉积的地质知识库。在对露头剖面数字化的基础上，利用已有的露头剖面的地质知识库资料进行变差函数的分析。通过分析获得吴官屯剖面辫状河沉积露头不同井距不同微相的变差函数以及相应的水平主变程与垂直变程比值的变化范围；其中，越岸沉积微相变化范围为2．7～42．2、心滩坝微相变化范围为24．6～54．8、辫状河道微相变化范围为8．9～15．5。结果表明：工区内越岸沉积微相主要是厚层状和薄条带状为主，心滩坝以厚层状为主，而辫状河道以窄厚状为主且规模相对其他微相较小。利用设置的剖面井数据应用序贯指示模拟得到对应模拟结果表明：随着条件数据点的增加）（3-4—6．11口井），模拟剖面与数字化剖面的吻合度逐渐增加，分别约为35％，50％，65％和75％；结果说明随着井距逐渐减小时，随机模拟结果与露头剖面逐步接近，模拟结果的不确定性逐渐降低。最后，通过不同井距的变差函数参数表与储层地质知识库数据表对比分析发现，沉积微相的变差函数与地质知识库的变化范围基本一致。这进一步证实在地质建模过程中，利用相似区露头建立详细的地质知识库指导建立地下地质模型是可靠和可信的。

Based on abundant sampling points, high resolution and direct observation of braided river outcrop data, the geological database of study area was establishesd. On the basis of digital outcrop profile, the geological database was applied to analyze variogram. The results show the followings： Firstly, the different microfacies variograms and corresponeding ratios extent of horizontal major range to vertical range are obtained from different well spaces of Wuguantun braided river outcrop, among which the ratio of overbank（OB） microfacies ranges from 2.7 to 42.2, while channel bar（CHB） microfacies are from 24.6 to 54.8 and braided channel（CH） microfacies are from 8.9 to 15.5. The results demonstrate that the sedimentary microfacies in the overbank of study area mainly show thick layer and thin strip shape, and the channel bars exhibit a thick layer shape, while the braided channel is relative smaller than other microfacies in shape of narrow thick. Secondly, the results gained by applying profile well data and sequential indicator simulation algorithm show that along with the condition data points increasing from 3 to 11, that simulation model ismore consistent with the digital outcrop profile with coincidence degree changing from 35% to 75%. Comparing the variogram parameter table of different well spaces experiments with outcrop geologic database, it is found spaces reduced, random simulation results are closer to the outcrop profile, with uncertainty decreased. It is concluded that the variogram parameter of sedimentary microfacies is essentially coincided with the range of geological database, which furtherly confirms that using a similar outcrop to build detailed geological database to guide establishing underground geologic model is reliable and credible.