During volume fracturing of shale gas reservoirs,hydraulic fractures may readily communicate with natural fractures to propagate forward and induce the formations to slip along the fracture surfaces.The resulted inter...During volume fracturing of shale gas reservoirs,hydraulic fractures may readily communicate with natural fractures to propagate forward and induce the formations to slip along the fracture surfaces.The resulted inter-well frac-hit and casing deformation affect the safe and efficient operation of shale gas fracturing.In addition,unpropped fractures caused by small natural fracture width lead to deteriorating fracture conductivity,which in turn impacts the stimulation effect of shale gas reservoirs.This paper discusses the three key issues,i.e.inter-well frac-hit,casing deformation and unpropped microfractures,that impact the economic exploration and exploitation of shale gas,and proposes engineering prevention and control measures through literature review and research on mechanism by integrating theoretical and experimental analysis,which have been applied on site.Firstly,after clarifying the mechanism and main controlling factors of inter-well frac-hit,an evaluation model and prediction method of frac-hit based on machine learning were established.The measures for preventing and controlling inter-well frac-hit,including temporary plugging at fracture tip and shut-in of old wells,were determined after evaluation with the well-cluster fracture model.Secondly,an analysis model of casing deformation caused by fracture shear and slippage was established after stress analysis.According to the analysis of stress on casing intersected with fractures during fracturing,it is ascertained that increase of fluid pressure within natural fractures is the main factor that causes casing deformation.The methods for preventing casing deformation were proposed in terms of fracturing operation and well construction.Thirdly,the mechanism of micro-proppant migration was analyzed by integrating the model of particle migration and the transport experiment in large-scale plate,and the experiment confirms that micro-proppant can effectively improve the fracture conductivity.It is concluded after field application that the prevention and control measures proposed for inter-well frac-hit and casing deformation can mitigate frac-hit and casing deformation significantly,and micro-proppants are conducive to improving post-frac shale gas production.The measures provide a support for large-scale and economic development of deep shale gas.展开更多
基于复合断裂力学解析方法和能量平衡原理,考虑非常规油气储层岩石高脆性和低渗透性特点,研究水平井分段压裂诱导裂缝间应力相互干扰条件下裂缝扩展的力学机制和缝内变密度支撑剂运移规律。根据水力压裂裂缝扩展的拟三维模型和考虑缝内...基于复合断裂力学解析方法和能量平衡原理,考虑非常规油气储层岩石高脆性和低渗透性特点,研究水平井分段压裂诱导裂缝间应力相互干扰条件下裂缝扩展的力学机制和缝内变密度支撑剂运移规律。根据水力压裂裂缝扩展的拟三维模型和考虑缝内流体沿缝长、缝高二维流动的全三维模型,分别考虑水平井单井缝网压裂和双井同步压裂形成网状裂缝状态,建立考虑缝间应力干扰的诱导网状裂缝体积压裂优化设计模型,采用Visual Studio 2012开发平台,研制设计软件3D-UGMulti-Fracture。根据断裂力学和渗流力学原理研究水力压裂过程中不同密度支撑剂在网状裂缝内的运移过程。利用微地震技术对同步压裂井实施裂缝监测,检测结果与软件计算结果具有很好的一致性。按照压裂工艺设计要求,优化排液量和砂比等参数,增加裂缝有效支撑长度,提高裂缝导流能力。展开更多
Two main challenges exist in enhancing oil recovery rate from tight oil reservoirs,namely how to create an effective complicated fracture network and how to enhance the imbibition effect of fracturing fluid.In respons...Two main challenges exist in enhancing oil recovery rate from tight oil reservoirs,namely how to create an effective complicated fracture network and how to enhance the imbibition effect of fracturing fluid.In response to the challenges,through modeling experiment in laboratory and evaluation of field application results,a set of integrated efficient fracturing and enhanced oil recovery(EOR)techniques suitable for tight oil development in China has been proposed.(1)Fracturing with temporary plugging agents to realize stimulation in multiple clusters,to form dense fracture network,and thus maximizing the drainage area;(2)Supporting induced fractures with micro-sized proppants during the prepad fluid fracture-making stage,to generate dense fracture network with high conductivity;(3)Using the liquid nanofluid as a fracturing fluid additive to increase oil-water displacement ratio and take advantage of the massive injected fracturing fluid and maximize the oil production after hydraulic fracturing.展开更多
文摘During volume fracturing of shale gas reservoirs,hydraulic fractures may readily communicate with natural fractures to propagate forward and induce the formations to slip along the fracture surfaces.The resulted inter-well frac-hit and casing deformation affect the safe and efficient operation of shale gas fracturing.In addition,unpropped fractures caused by small natural fracture width lead to deteriorating fracture conductivity,which in turn impacts the stimulation effect of shale gas reservoirs.This paper discusses the three key issues,i.e.inter-well frac-hit,casing deformation and unpropped microfractures,that impact the economic exploration and exploitation of shale gas,and proposes engineering prevention and control measures through literature review and research on mechanism by integrating theoretical and experimental analysis,which have been applied on site.Firstly,after clarifying the mechanism and main controlling factors of inter-well frac-hit,an evaluation model and prediction method of frac-hit based on machine learning were established.The measures for preventing and controlling inter-well frac-hit,including temporary plugging at fracture tip and shut-in of old wells,were determined after evaluation with the well-cluster fracture model.Secondly,an analysis model of casing deformation caused by fracture shear and slippage was established after stress analysis.According to the analysis of stress on casing intersected with fractures during fracturing,it is ascertained that increase of fluid pressure within natural fractures is the main factor that causes casing deformation.The methods for preventing casing deformation were proposed in terms of fracturing operation and well construction.Thirdly,the mechanism of micro-proppant migration was analyzed by integrating the model of particle migration and the transport experiment in large-scale plate,and the experiment confirms that micro-proppant can effectively improve the fracture conductivity.It is concluded after field application that the prevention and control measures proposed for inter-well frac-hit and casing deformation can mitigate frac-hit and casing deformation significantly,and micro-proppants are conducive to improving post-frac shale gas production.The measures provide a support for large-scale and economic development of deep shale gas.
文摘基于复合断裂力学解析方法和能量平衡原理,考虑非常规油气储层岩石高脆性和低渗透性特点,研究水平井分段压裂诱导裂缝间应力相互干扰条件下裂缝扩展的力学机制和缝内变密度支撑剂运移规律。根据水力压裂裂缝扩展的拟三维模型和考虑缝内流体沿缝长、缝高二维流动的全三维模型,分别考虑水平井单井缝网压裂和双井同步压裂形成网状裂缝状态,建立考虑缝间应力干扰的诱导网状裂缝体积压裂优化设计模型,采用Visual Studio 2012开发平台,研制设计软件3D-UGMulti-Fracture。根据断裂力学和渗流力学原理研究水力压裂过程中不同密度支撑剂在网状裂缝内的运移过程。利用微地震技术对同步压裂井实施裂缝监测,检测结果与软件计算结果具有很好的一致性。按照压裂工艺设计要求,优化排液量和砂比等参数,增加裂缝有效支撑长度,提高裂缝导流能力。
基金Supported by the China National Science and Technology Major Project(2016ZX05051-03,2016ZX05030-05)PetroChina Innovation Foundation(2018D-5007-0205)the Science Foundation of China University of Petroleum at Beijing(2462017YJRC031).
文摘Two main challenges exist in enhancing oil recovery rate from tight oil reservoirs,namely how to create an effective complicated fracture network and how to enhance the imbibition effect of fracturing fluid.In response to the challenges,through modeling experiment in laboratory and evaluation of field application results,a set of integrated efficient fracturing and enhanced oil recovery(EOR)techniques suitable for tight oil development in China has been proposed.(1)Fracturing with temporary plugging agents to realize stimulation in multiple clusters,to form dense fracture network,and thus maximizing the drainage area;(2)Supporting induced fractures with micro-sized proppants during the prepad fluid fracture-making stage,to generate dense fracture network with high conductivity;(3)Using the liquid nanofluid as a fracturing fluid additive to increase oil-water displacement ratio and take advantage of the massive injected fracturing fluid and maximize the oil production after hydraulic fracturing.
