页岩剪切摩擦与非稳态滑移特性实验

Experiments on Friction and Non-Steady Slip for Shale

龙一1亚段页岩是川南页岩气开发的主要目的层,实践表明水平井单井产气量对井轨迹所在小层较为敏感.龙一1亚段页岩各层脆性矿物组分、弹性模量变化幅度小,采用常规页岩脆性评价方法和模型不能有效评价川南龙一1亚段各小层页岩的可压性,借鉴地震学地震成核原因研究思路,提出利用稳态-非稳态破坏特征来表征各小层可压性.优化设计一种页岩剪切摩擦、稳态-非稳态特性实验方法,利用川南页岩地面露头进行线切割制样开展相关实验测试,分析研究页岩摩擦系数受层理性构造、矿物组分、法向应力大小的影响,表征量化不同矿物组分下的页岩稳态-非稳态特征,确定了速度弱化向速度强化转换的粘土矿物含量临界值.以川南昭通YS108井区龙一1亚段页岩储层为例,对各小层可压性进行整体评价,得到:龙一^1~21层较易开启剪切滑移,且易形成网状裂纹,储层整体可压性好;龙一^31层较难开启剪切滑移,但裂纹为单一裂纹、网状裂纹过渡状态,储层整体可压性较差;龙一^41层较易开启剪切滑移,但裂纹则呈现单一状态,储层整体可压性较差.

L11 sub-section shale reservoir is the major production layer in the South Sichuan shale gas block.For the horizontal well production,different well paths in the different layers can show quite big production gap,which may be due to the different shale crushabilities.However,the elastic modulus and brittle minerals for different layers in L11 sub-section have not shown much difference,so it is still impossible to evaluate the shale brittleness sufficiently with the conventional methods and models,Based on studies on the cause of earthquake,the steady&non-steady state failure is introduced to characterize the crushability for the different L11 layers in this paper.The new friction and steady&non-steady state experiments were designed to replace the conventional fault gauge testing method for the L11 outcrop samples.Firstly,the influence of the lamination,mineral constituents and normal stress on the friction for shale was studied and analyzed.Secondly,the steady&non-steady state behavior was characterized and quantified by the calculated a-b value for the shale with different mineral constituents.Thirdly,the critical value from velocity-weakening to velocity-strengthening was established by the overlay method.Taking Well YS108 field in Zhaotong shale block as the example,the different crushabilities for different layers were analyzed and discussed.It is found that L1^1-21 layers have better crushability that can cause the shear slide easily and generate the map cracking,while the L1^41 layers have worse crushability that generates the single cracking or cause the shear slide difficultly.