川东南东溪地区龙马溪组裂缝分布预测及页岩气保存条件评价

Prediction of fracture distribution and evaluation of shale gas preservation conditions in Longmaxi Formation in Dongxi area

  • 摘要: 页岩气的商业性开发证实成熟页岩具有较大的勘探潜力,川东南地区是我国南方页岩气勘探开发的战略先导区。裂缝发育情况是页岩气保存和开发部署的关键因素,对于构造环境复杂特殊的盆缘地区,在加大页岩裂缝研究难度的同时,也给页岩气勘探开发提供了新的方向。页岩气勘探作为我国油气勘探的新领域,尚未形成成熟的裂缝评价体系。以川东南东溪地区为例,基于三轴岩石力学实验结果,首先采用有限元数值模拟手段进行应力场模拟,而后利用岩石力学参数进行模型构建和模拟结果的反复试算,以获取东溪地区最大、最小主应力和应力差分布图,最后运用莫尔–库伦准则计算岩体破裂系数预测裂缝分布规律。结果表明:研究区裂缝发育情况主要分为4个级别,其中,Ⅰ级裂缝呈条带状分布在东西两侧断裂附近,Ⅱ级裂缝在Ⅰ级裂缝周围发育,而Ⅲ级裂缝分布在北部背斜核部和西部背斜翼部;优选页岩气埋深、距剥蚀区距离、距齐岳山断裂距离、断裂作用、应力差及压力系数等10个保存条件参数,采用组合权重法确定保存条件参数权重,其中一级参数权重分别为埋深(0.2)、距剥蚀区距离(0.1)、距齐岳山断裂距离(0.1)、断裂作用(0.25)、应力差(0.15)、压力系数(0.2),以此建立相对完善的页岩气评价体系与评价标准。优选出2类页岩气勘探目标有利区,其中A类、B类有利区分别分布在研究区南部背斜核部及翼部和中部宽缓褶皱两翼。研究成果为川东南地区的页岩气勘探提供重要的参考价值。

     

    Abstract: Commercial development of shale gas confirmed that mature shale has great potential for exploration, southeast Sichuan is the strategic pilot area of shale gas exploration and development in southern China, cracks are the key factor of shale gas preservation and development deployment, for the structural environment complex and special basin edge area, increasing the difficulty of shale crack research, but also provides a new direction for shale gas exploration and development. As a new field of oil and gas exploration in China, shale gas exploration has not yet developed a mature crack evaluation system. Taking Dongxi area of the southeast of Sichuan as an example, the stress field was simulated in the region by finite element numerical simulation. The model was constructed and calculated by rock mechanical parameters, the diagrams of maximum principal stress, minimum principal stress and differential stress distribution in Dongxi area were obtained through repeated debugging of the simulation results. Mohr-Coulomb criterion was used to calculate rock fracture coefficient and to predict the law of crack distribution in the study area, The prediction shows that the crack distribution of the study area is divided into four levels, GradeⅠcracks are distributed in bands near the east and west sides, grade cracks develop around gradeⅠcracks, the grade cracks are distributed in the northern dorsal nucleus and the western dorsal wing, respectively. At the same time, 10 preservation condition parameters, such as shale gas burial depth, distance from the ablative area, fracture distance from Qiyun Mountain, fracture action, differential stress and pressure coefficient, were clarified, and were used to determine the primary and secondary parameter weight by the combined weight method. Among them, the first stage parameters are buried depth(0.2), distance from the exfoliation area(0.1), fracture distance(0.1), fracture action(0.25), differential stress(0.15), and pressure coefficient(0.2). A relatively sound shale gas evaluation system and evaluation standards have been established. The two types of shale gas exploration targets are preferred, the favorable areas of the typeⅠand the typeⅡare located in the core and wings of the anticline core in the south of the study area and wings of the gentle folds in the middle of the study area, This study provides an important reference for shale gas exploration in southeast Sichuan.

     

/

返回文章
返回