泸州北区深层页岩现今地应力场分布特征及扰动规律

Distribution Characteristics and Pattern of Deep Shale Present Geostress Field in Northern Luzhou

地应力场特征分析评价是深层页岩气勘探开发的重要环节,对压裂裂缝走向预测、井网部署和水平井位部署具有重要的指导意义。以四川盆地泸州北区龙一1亚段为例,通过室内实验、测井解释对比和应力场模拟预测,建立了岩石力学动静态参数转换关系式,明确单井地应力特征,完成应力场扰动分析,实现了对研究区应力场的分区刻画。结果表明:(1)岩石力学参数呈现出“高杨氏模量、低泊松比”的特征,表明目的层具有较高的脆性。三向应力随埋深的增加而增大,且表现为水平最大主应力>垂向主应力>水平最小主应力。(2)4种应力方向判别方法的对比分析得出,研究区水平最大主应力方向在105°~115°。福集向斜相对于区域应力方向发生逆时针偏转,在75°~85°,得胜向斜常保持区域应力方向。(3)对比区域应力状态,背斜区受张应力影响,应力值减小、应力方向顺时针偏转;受挤压应力的影响,向斜区表现出相反的趋势。断裂对应力扰动最大范围可达1.8 km,不同走向断裂对应力扰动强度排序为NEE、NE和NNE。(4)依据断裂和应力场扰动的特征,将研究区划分为调整带、转换带和稳定带3种类型。这为后续研究区开发单元的优化提供了有效支撑,实现单井平均经济可采储量稳步上升。

Stress field characterization and evaluation is an important part of deep shale gas exploration and development,and is important in guiding the prediction of fracture crack direction,well network deployment,and horizontal well location deployment.Using the Longyi 1 subsection in Luzhou North District,Sichuan Basin,as an example;through indoor experiments,logging interpretation comparison,and stress field simulation prediction;we established the conversion relation equation of rock mechanics dynamic and static parameters,clarified the single well geostress characteristics,and completed the stress field perturbation analysis.This enabled us to realize the zoning portrayal of the stress field in the study area.The results of the study showed that:①the rock mechanical parameters show the characteristics of“high Young’s modulus and low Poisson's ratio,”which indicates that the target layer is highly brittle.The three-directional stress increased with increasing burial depth,and the relationship between the stresses was as follows:S_(H)>S_(v)>S_(h).②A comparison and analysis of the four stress direction discrimination methods showed that the maximum horizontal principal stresses in the study area ranged 105-115°.The Fuji oblique inclination was deflected counter-clockwise with respect to the regional stress direction in the range 75-85°,whereas the Desheng oblique inclination often maintained the regional stress direction.③Comparing the regional stress state,the dorsal inclined area was shown to be affected by the tensile stress,with the stress value decreasing and the stress direction being deflected clockwise,whereas the oblique inclined area showed the opposite tendency owing to the influence of the extruding stress.The maximum range of stress perturbation by fractures reaches up to 1.8 km,and the intensity of stress perturbation by fractures with different strikes is ranked as NEE,NE,and NNE.④Based on the characteristics of fractures and stress field perturbations,the study area was classified into three types:adjusting,transforming,and stabilizing zones.The results of this study provide effective support for the optimization of subsequent development units to achieve a steady increase in the average EUR of a single well.