沾化凹陷渤南洼陷超压裂缝的测井响应特征与预测

Logging response of overpressure fractures and their prediction in Bonan sag,Zhanhua depression

通过岩心观察、成像测井识别与常规测井资料分析相结合的方法,对渤南洼陷烃源层系内超压裂缝的特征、测井响应标志及预测进行研究。结果表明:渤南洼陷超压源岩层系中裂缝发育,裂缝数量和规模不一,在成像测井上表现为中高角度、倾向杂乱的高导缝;常规测井曲线具有高声波时差、高补偿中子孔隙度、高密度、高地层真电阻率变化率和低自然伽马变化率的'四高一低'的响应特征;超压裂缝大量发育于地层压力系数大于1.2且压力梯度变化大的区域,在压力梯度变化较小的高压区域,可识别裂缝的数量较少、规模较低;超压裂缝带具有横向上连续、纵向上分段的特征,与油气的空间分布匹配性较好,是超压体控制下源岩排烃的重要通道。

Based on core observations and imaging the forming logging and conventional logging, the logging responses of the overpressure fractures and their distribution within the source rocks were analyzed in Bonan sag, Bohai Bay Basin. Many fractures are observed in the Third Member of Shahejie Formation with high overpressure, but their quantity and scales are different. Overpressure fractures show highly conductive feature with middle-high angle and disorder inclination in the ima-ging logging data, and they always have distinctive features such as high rate of change of AC, CNL, DEN, Rt and low rate of change of GR in conventional logging curves. Fractures produced by overpressure are greatly developed in those areas where pressure coefficients are bigger than 1. 2 and pressure gradient changes rapidly, while fractures of smaller scale are also developed in the overpressure areas where the pressure gradient changes slowly. As the main primary migrating pathway, the fracture zones within overpressure source rocks affect the spatial distributions of hydrocarbons. Fracture zones are laterally continuous and are distributed in several segments on the longitudinal direction, which agrees well with the distribution of hy-drocarbons in Bonan sag.