抗高温高密度油基钻井液体系静态沉降稳定性建模及优化

Modeling and Optimization of Static Settlement Stability of High Temperature Resistance and High Density Oil-based Drilling Fluid System

抗高温高密度油基钻井液可用于复杂地层钻井,利于井壁稳定,可用于钻大位移井、水平井、超深井等,但在高温状态下面临钻井液沉降问题。钻井液的沉降包括静态沉降和动态沉降,过去主要关注钻井过程中钻井液的动态沉降,但由于钻井液具有剪切稀释性,一般静态条件下沉降稳定性较好的钻井液体系在较高剪切速率下仍具备良好的稳定性,主要研究高温状态下油基钻井液体系的静态沉降稳定性。为使体系达到较好的静态沉降稳定性,以往对各类核心处理剂,乳化剂、有机土、重晶石和油水比的加量和配比只做出试探性调整,实验存在一定盲目性,不能确定实验周期。针对上述问题,分析室内和现场密度2.5 g·cm-3柴油基钻井液流变参数与静态沉降密度差的相关性,建立数学函数模型;将模型反馈的流变参数值与实验结合起来,利用模型优化基础实验,调整处理剂加量至相应流变参数值,使体系静态沉降密度差最小;最终得到一组抗温190℃,密度2.5 g·cm-3沉降稳定性好的油基钻井液体系。研究过程具有目的性,体系静态沉降稳定性建模方法和实验模型结合的方法为优化钻井液体系性能提供了一种新思路。

High-temperature resistance and high-density oil-based drilling fluid can be used to drill through complex formations,and can be used to drilling large displacement wells,horizontal wells,super deep wells,etc.Yet,the drilling fluid has settlement problems under high temperature conditions.Settlement stability of drilling fluid includes static settlement and dynamic settlement.In the past,the dynamic settlement of drilling fluid was mainly considered during drilling process.However,due to the shear dilution of drilling fluid,the drilling fluid system with good settlement stability under static conditions still has good stability under high shear rate.Therefore,the static settlement stability of oil-based drilling fluid system under high temperature was studied.To achieve better static settlement stability of the system,the dosage and ratio of various core reagents,emulsifier,organic soil,barite,and oil-water ratio were tentatively adjusted only in the past,the regarding experiments were aimless to some extents,and the experiment cycle could not be determined.To solve these problems,correlation between rheological parameters of diesel-based drilling fluid in density of 2.5 g·cm-3 and the static settlement density difference was analyzed,and a mathematical function model was established.In addition,the rheological parameter value fed back by the model with the experiment was combined,the basic experiment was optimized by using the model,the dosage of the treatment agent to the corresponding rheological parameter value was adjusted,and the static settlement density difference of the system was minimized.At last,a group of oil-based drilling fluid system with good stability against temperature 190℃and density 2.5 g·cm-3 was obtained.The research process was well intended.The combination of static settlement stability modeling and experimental model of the system provided a new idea for optimizing the performance of drilling fluid system.