超深井钻井液污染套管机理

Mechanisms Casing Contamination by Drilling Fluids in Ultra-Deep Well Drilling

针对超深井钻井过程中钻井液对套管的污染问题,分析了超深井环境下钻井液在套管壁的残留率,明确温度是影响钻井液残留的主要因素。在超深井高温下,油基钻井液发生破乳效应,由疏水转变为弱亲水性;水基钻井液发生脱水效应,由亲水转为弱疏水性。采用XRD、元素分析、四组分、傅里叶红外光谱等测试方法,对钻井液残留物的成分进行分析,得到水基钻井液残留物的主要成分为纤维素、磺化酚醛树脂携带包裹黏土颗粒与重晶石混合物;油基钻井液残留物主要成分为沥青和油酸酰胺包裹重晶石混合物。结合测试分析结果,通过分子动力学模拟计算钻井液中大分子在套管壁上的吸附效应,得到沥青主要成分卟啉和油酸酰胺与套管壁的结合能分别为-54.18 kcal/mol和-19.72 kcal/mol,纤维素和磺化树脂与套管壁的结合能分别为-19.09 kcal/mol和-93.19 kcal/mol,证实了水基钻井液中有机组分在高温状态下较油基钻井液更具有黏附性。通过对钻井液污染机理的分析,为日后套管清洗提供理论性指导。

By analyzing the residual rate of drilling fluids on the surfaces of casing strings in ultra-deep wells,it was ascertained that temperature is the main factor affecting the residue of drilling fluids on the surfaces of the drilling strings.In high temperature ultra-deep wells,oil-based drilling fluids are apt to lose their emulsion stability and become demulsified,turning from hydrophobic to hydrophilic.Water-based drilling fluids,on the other hand,are dewatered at elevated temperatures,turning from hydrophilic to hydrophobic.Using XRD,element analysis,SARA and FTIR methods,the components of the residues of a water-based drilling fluid and an oil-based drilling fluid commonly used were analyzed.The main components of the residues were known to be cellulose and the mixture of clay and barite particles coated with sulfonated phenolic resin for the water based drilling fluid,and asphalt and barite coated with oleic acid amide for the oil-based drilling fluid.The adsorption effect of the macromolecules in a drilling fluid on the surfaces of casing strings was calculated using molecular dynamics simulation based on the analyses of the residues in the drilling fluids.The calculation showed that the binding energy between porphyrin(the major component of asphalt)and the casing wall is-54.18 kcal/mol,the binding energy between oleic acid and the casing wall is-19.72 kcal/mol,the binding energy between cellulose and the casing wall is-19.09 kcal/mol,and the binding energy between sulfonated phenolic resin and the casing wall is-93.19 kcal/mol,respectively.These results have proved that compared with oil-based muds,the organic components in a water-based are much more adhesive at elevated temperatures.This analysis of the casing contamination by drilling fluids will provide theoretical guidance to the cleansing of casing strings in the future.