超高密度复合盐水钻井液流变性调控及应用

Lu206井是四川盆地南部泸县长宁地区油气页岩气勘查区块的一口评价井，目的层为宝塔组。该井直导眼井井深为4082 m，实际钻井过程中钻遇高压裂缝气导致所施工的最高水基钻井液密度为2.42 g/cm3，气层活跃井控风险大，必须维持钻井液具有超高密度，由于密度超高导致固相控制难度大，还因为上部泥岩地层易造浆，所以导致调控钻井液体系的流变性困难。总结区域内钻井经验，通过系统的室内实验研究，将上部聚磺钻井液体系转换成抗污染能力、抑制性强的超高密度复合盐水钻井液。该复合盐水钻井液在实践中也面临着流变性调控的难点，加强现场理论分析和小型试验，优选出了一种褐煤树脂KJ-4，将KJ-4、高密度分散剂、磺化单宁一起复配，在Lu206井直导眼井四开进行了超高密度复合盐水钻井液的试验。结果表明，该复配组合能较好地调控复合盐水流变性，控制超高密度复合盐水钻井液的黏度和切力，为该区块高密度钻井液流变性的调控提供了一种解决思路。 

Rheology Control and Application of Ultra-High-Density Compound Brine Drilling Fluid

Well Lu-206 is an appraisal well drilled in the oil/gas and shale gas exploration block in Changning, Lu County, south of Sichuan Basin. The target zone of this well is the Baota Formation. The vertical pilot hole of this well is 4082 m in depth. During drilling operation, high pressure fracture gas was encountered, caused the hole to overflow, and the well was finally killed with a high density (2.42 g/cm3) water base mud. To control the formations wit active gas, ultra-high density had to be used, this in turn resulted in difficulties in solids control of the drilling fluids. Furthermore, the top formations are very water sensitive, making control of mud rheology is very difficult. Based on the past drilling experiences gained and comprehensive laboratory experiment, the sulfonate polymer drilling fluid previously used to drill the top section of the well was replaced with an ultra-high-density compound brine drilling fluid with excellent contamination resistance and inhibitive capacity. A lignite resin KJ-4, a high-density dispersant and a sulfonated tannin were mixed together to control the rheology of the compound brine drilling fluid, which was also a problem needed to be resolved. Application of this ultra-high-density compound brine drilling fluid in drilling the fourth interval of the vertical pilot hole of the well Lu-206 showed that the rheology of the drilling fluid was under control during the whole drilling process. The success of the field practice has provided a clue for controlling the rheology of high-density drilling fluids.