常规测井对煤系致密砂岩储层裂缝敏感性分析

Sensitivity of Conventional Well-logging Series to Fractures in Tight Sandstone Reservoirs with Coal

煤系致密砂岩储层具有压实程度高、单层厚度小、强非均质性及强各向异性特征,裂缝预测难度大。利用具有高分辨率优点的测井资料进行裂缝评价是一种较为有效的手段。利用变尺度分形概率法对常规测井系列进行数学代换,分析各个常规测井系列对裂缝的敏感性。对纵波时差、密度、自然伽马、浅侧向电阻率、深侧向电阻率及自然电位6条常规测井曲线进行了分形概率分析。该分析法的权重值取1,分形阀值取1。分析认为,山西组煤系致密砂岩裂缝的存在主要能在声波时差及电阻率测井系列中产生较为显著的响应,同时能在自然伽马和密度测井系列中产生弱响应,而裂缝发育程度与自然电位测井参数的关系不显著。因此,在对强非均质性煤系致密砂岩储层裂缝进行模拟或预测时,可优选声波时差、电阻率、自然伽马及密度4个常规测井系列参数,而自然电位则不建议采用。

Most tight sandstone reservoirs with coal are characterized by high compaction, a little thickness of single layer, and strong heterogeneity and anisotropy, resulting in great difficulty to predict fractures in these reservoirs. However, well-logging data with high resolution is exactly useful. Mathematic exchanging is implemented to the conventional well-logging series by means of variable scale fractal probabilistic method. Then, the sensitivity of these series to fractures may be analyzed. For six conventional welllogging curves containing compressional slowness, density, natural gamma, shallow and deep lateral resistivity, and SP, their fractal probability was analyzed and gained. In this analysis method,weight value and fractal threshold value were individually taken to1. Results show that, in the Shanxi Formation of tight sandstone reservoirs with coal, fractures may generate an obvious response in both compression slowness and resistivity well logging whereas weaker in natural gamma and density logging; and the relation between fracture growth and SP logging parameters is not significant.So, during simulating and predicting these fractures, four kinds of parameters from compressional slowness, resistivity, natural gamma, and density logging should be optimized, however SP logging is not preferred.