井壁强化技术的研究及其在乐东区块的应用

A Study on Borehole Wall Strengthening Technique and Its Application in Block Ledong

乐东区块构造位于莺歌海盆地的凹陷斜坡带,属于典型的海上超高温高压区块,地层安全密度窗口窄,深层井漏问题突出,严重制约了乐东气田的勘探与开发。针对该区块的井漏技术难题,通过井史资料统计,分析了该区块的漏失特征及漏失机理。基于黏滞单元法,模拟了井壁强化作用前后的井周应力变化,并预测了预充填裂缝开度。基于新型可变裂缝封堵模拟实验装置,开展了井壁强化材料粒径及浓度优化实验研究。实验结果表明,较优粒度匹配准则为D_(50)准则,合理浓度为5%。基于乐东区块抗高温油基钻井液,优化构建了井壁强化钻井液体系配方。综合评价表明,该井壁强化配方对钻井液的流变性影响较小,砂床滤失侵入深度仅为1.5 cm,1 mm动态裂缝封堵承压能力达12 MPa以上。

The Ledong block,a typical high temperature high pressure offshore block,is located in the depression slope zone of the Yinggehai Basin.Some formations drilled in this block have narrow safe drilling windows and mud losses in deep hole occurred frequently during drilling.To deal with the mud losses,the drilling data was studied and the mechanisms and nature of the mud losses were analyzed.Using the viscous element method,the change of the stresses around the borehole before and after borehole wall strengthening was simulated,and the opening of the prefilled fractures predicted.Using a new experiment apparatus which can simulate the plugging of variable fractures,a study was conducted on the particle size distribution and concentration optimization for borehole wall strengthening.The experimental results show that the D_(50) criterion is a better particle size matching criterion,and a reasonable concentration of the particles is 5%.A drilling fluid that is suitable for use in the Ledong block and has the ability of borehole wall strengthening is developed through optimization experiment.In a comprehensive evaluation experiment,the additives for borehole wall strengthening showed little effects on the rheology of the drilling fluid.Sand bed test showed that the depth of the filtrate invasion was only 1.5 cm.Dynamic pressure bearing capacity of 1mm fractures tested with the drilling fluid can be as high as 12 MPa.