加权断层泥比率法(WSGR)定量判别断层封闭性——以苏北盆地高邮凹陷永安地区为例

Quantitative evaluation of fault sealing by Weighted Shale Gouge Ratio(WSGR):a case study of Yongan area in Gaoyou Sag,Subei Basin

断层封闭性评价是断块圈闭成藏条件分析的重要内容,在改进断层泥比率法基础上,提出了一种新的断层封闭性评价方法——加权断层泥比率法(WSGR)。首先,通过不同的地质模型开展断层泥比率法计算参数及影响因素分析,明确了断层断距、泥质含量及泥岩分布特征是泥岩涂抹的重要影响因素;并认为断层断距范围内,滑过目标位置的对置盘所有泥质含量都具有涂抹贡献,但不同点的涂抹贡献不同,距离目标位置越近泥质含量越高的对置盘泥岩点,其涂抹贡献越大。为此引入了一个新的表征参数——距离系数,定义为断层断距与各泥岩点到目标位置距离的差与断层断距的比值,来表征泥岩分布对泥岩涂抹的影响作用;在此基础上,构建了加权断层泥比率计算方法,定义为各点的泥质含量与距离系数的乘积之和再与距离系数之和的比值。利用加权断层泥比率法对苏北盆地高邮凹陷上含油气系统已知的油水层进行封闭性验证,认为当加权断层泥比率值大于0.6时,断层具有较好的封闭性,从而确定了该方法的封闭性判别标准。在高邮凹陷永安等地区始新统戴南组断层封闭性评价中取得了较好应用效果。

The evaluation of fault sealing is an important part of analyzing hydrocarbon accumulation conditions in fault-block traps.Based on the improved Shale Gouge Ratio(SGR),this paper proposed a new method for evaluating fault sealing,Weighted Shale Gouge Ratio(WSGR).Firstly,the calculation parameters and influencing factors of SGR were analyzed using different geological models,and it is determined that fault distance,mud content,and mud rock distribution are important factors affecting shale smear.It was found that all muddy sediments that slide through the target reservoir have contributions to shale smear within fault distance,but the contributions of different points vary,with higher mud content and closer distances contributing more.Therefore,a new parameter called distance coefficient was introduced to represent the influence of mudstone distribution on shale smear.The distance coefficient is defined as the ratio of the difference between fault distance and the distance from mudstone to the target reservoir to the fault distance.Based on this,a calculation method named Weighted Shale Gouge Ratio(WSGR)was constructed,which is defined as the product of mud content and distance coefficient at each point,summed and divided by the sum of distance coefficients.The sealing performance of known oil and water layers in the upper oil and gas bearing system in the Gaoyou Sag is verified by using Weighted Shale Gouge Ratio(WSGR),and it is considered that when the value of WSGR is greater than 0.6,the fault has good sealing performance,thus determining the sealing discrimination criteria of this method.Finally,good application results have been achieved in the evaluation of fault sealing of Eocene Danan Formation in Yongan and other areas of the Gaoyou Sag.