倾角对裂缝密度反演的影响分析

在倾斜裂缝中,能不能利用普遍使用的裂缝发育强度近似公式进行裂缝密度评价,是一个值得讨论的问题。由TTI介质反射振幅方程出发,推导出与HTI介质裂缝密度计算公式相似的TTI介质的裂缝密度计算公式；通过对两个公式的对比分析,建立了裂缝倾角影响裂缝密度计算结果的理论基础；通过数值计算,绘制了裂缝密度与裂缝倾角的关系曲线,对裂缝倾角的影响程度进行了量化分析,得出在设计的代表性模型中,当裂缝倾角小于80°时,利用简化公式评价裂缝密度,将使结果产生较大偏差的结论。依据塔河油田裂缝型储层设计了TTI介质和HTI介质模型,正演模拟结果验证了上述结论的正确性,同时还发现裂缝倾角对裂缝密度评价的影响甚至大于数据噪声引起的误差。基于此,提出对于倾斜裂缝介质，不能直接利用简化公式计算裂缝密度的建议。

Analysis on the impact of dip on fracture density inversion

Can we use common fracture growth intensity approximate formula for fracture density evaluation in dip fracture? It is worth for discussion.Starting from reflecting amplitude equation of TTI medium,the fracture density formula of TTI medium was gained,which is similar with that of HTI medium.Through comparison on the two formulas,the basic theory for fracture density calculations varying with its dip was built.Then,by numerical calculation,the relationship curve of fracture density and dip was plotted,and the impact of fracture dip was quantitatively analyzed.The results indicate that in the representative designed model,when fracture dip is smaller than 80°,large deviation will be obtained by evaluating fracture density through simplified approximate formula.The forward modeling results of TTI and HTI medium models designed in terms of fractured reservoirs of Tahe Oilfield prove the above conclusions.Meanwhile,it is found that the impact of fracture dip on its density evaluation is even larger than the error caused by data noise, So, we suggest that it couldn't directly use the simplified for mula for fracture density calculation in dip fractured medium.