连续油管调制局部欠平衡钻井水力特性研究

Along with the development of the petroleum exploration and production at the deep formation the chance to drill the hard formation increases and the rate of penetration decreases. In order to solve this problem the project have put forward a partial under balance drilling method modulated by coild tubing. The new method separates the annular into two parts using the annular packer respectively circulating high density drilling fluid and low density drilling fluid. The micro annular produced by coild tubing and drilling pipe changes general carying cuttings passageway and achieves high efficient carying cuttinigs with low flow rate. Cate to the hydraulic problems the project will study the annular flow field of bit bottom and near the backflow connector and optimize the structure and location of the backflow connector, compute pressure filed, velocity field, solid phase particle distribution and migration law in the different eccentricity in the micro annular formed by different size of outer wall of coiled tubing and internal wall of drilling pipe. The project will also design experimental facility to test the hydraulic parameters of micro annular and near bit,under balace drilling difference pressure, migration characteristics of cuttings, and verify the result of numerical simulation. It is expecter that the research results can provide theoretical foundation for the new underbalanced drilling method and improving rate of penetration in the deep well.

随着我国石油天然气勘探开发向深部地层发展，硬地层钻遇较多，机械钻速随之降低。针对这一问题,提出了连续油管调制局部近钻头欠平衡钻井提速新方法：利用环空封隔器将环空分为上下两段，分别循环高密度、低密度钻井液实现近钻头局部欠平衡；通过连续油管下入钻杆内形成微环空，改变传统钻井携岩通道，实现小排量高效携岩。针对其中的水力学问题，计划利用数值模拟方法研究钻头底部及回流短接附近环空流场，优化回流短接结构及位置；研究连续油管-钻杆微环空不同偏心率条件下压力场、速度场、固相颗粒分布及运移规律，回归得出微环空携岩模型；设计微环空及近钻头水力参数特性测试实验装置，测试欠平衡压差大小、岩屑运移特性等，验证数值模拟结果。研究结果可望为深井实施新型欠平衡钻井、提高机械钻速提供理论基础。

随着石油勘探开发的推进，钻遇硬地层、井壁稳定性差地层的可能性越来越高。常规钻井方法很难在提高机械钻速的同时保持较好的井壁稳定，为此结合欠平衡钻井方法以及连续管钻井，提出了连续管调制局部欠平衡钻井方法，并对该方法进行了基础理论研究。本课题共进行了4项研究内容：.（1）通过数值模拟研究发现当开孔数为4、开孔中心距井底300mm、开孔直径为50mm、开孔角度为120°时，回流装置的携岩能力最优。在以井底和井壁为壁面条件下，上返流体与喷嘴高速射流相互扰动形成复杂的井底流场，在射流两侧形成低速漩涡。对比脉冲射流和无脉冲射流情况，发现脉冲射流可降低瞬时井底岩屑浓度，当脉冲频率为4-8Hz时，井底清岩效果更好。.（2）在相同的排量下，小水力直径微环空的携岩能力更强。在微环空内流体的带动下，岩屑随着排量的增加，运移速度增加；随着转速的增加，岩屑向外侧移动，偏离微环空内高速流核区，导致岩屑运移速度降低。.（3）在设计的透明微环空实验架的基础上进行了岩屑运移实验，采用片状岩屑和铝球作为两种不同的岩屑颗粒。通过实验发现在微环空内铝球之间发生碰撞、速度变化等现象，片状岩屑在微环空内翻转上升。通过对比两种岩屑的运移速发现随着转速的增加，岩屑运移速度均降低，片状岩屑的运移速度大致为铝球颗粒的2.5倍。.（4）设计了连续管调制局部欠平衡钻井实验装置，通过压差实验发现系统压耗与排量呈幂函数关系，指数为2.1。软件计算压耗与实验的误差为5.56%，在可接受范围内。.项目研究成果共发表SCI 论文7 篇，EI 论文2 篇；申请国家发明专利3 件，均已授权；共做学术会议报告5次。