钻井工程中泥页岩井壁稳定的力学分析

分析了泥页岩井壁稳定的基本原理及影响因素.根据岩石力学理论推导了井眼围岩应力分布的具体表达式,结合胜利油田的实际.给出了岩石拉伸破坏和剪切破坏的强度准则.推导了确保井壁稳定的合理钻井液密度范围的计算公式.通过程序运算.分析了原地应力状态、地层孔隙压力、井深、井斜角、方位角等因素对井壁稳定的影响.结果表明.井壁稳定问题是受多种因素影响的。系统工程”.要解决这一问题必须局限到具体区域.确定各有关因素后.才能定量解答.以胜利油田牛20断块为例.介绍了该理论在实际工作中的应用情况.

MECHANICAL ANALYSIS OF BOREHOLE STABILITY IN SHALE FORMATION IN DRILLING

Shale formation is one of the most troublesome formation in drilling. Shrinkage or collapse often occur, seriously affecting exploration and development. Data on this research are not sufficient to date, and there is no satisfactory way to prevent and solve the problem. The paper analyses the principle of borehole stability and related factors. On the basis of rock mechanics theory, the paper derives the stress distribution in the vicinity of borehole and equations of mud weight, range required to prevent hole instability. Computer analysis shows the influence of the related factors, such as in-situ stress, pore pressure, depth of hole, inclination angle, azimuth angle, etc. Thus borehole stability involves a number of factors, and can be solved quant to lively in a specific area only where the factors are identified. The paper gives an example in Niu-20 block of Shengli oilfield, which indicates that the theory can be used to correctly predict the mud weight range to maintain hole stability.