超临界二氧化碳钻井岩屑速度分布数值模拟研究

Numerical Simulation Study on Cuttings Velocity Distribution in Supercritical Carbon Dioxide Drilling

超临界二氧化碳钻井技术能有效发现和保护油气藏,提高机械钻速,降低成本,对开发非常规油气资源有着巨大的优势.基于计算流体力学理论,考虑超临界二氧化碳物理特性,分析了超临界二氧化碳钻井液温度、压力、流速和钻杆偏心度、屈曲条件对岩屑速度分布的影响规律.结果表明:温度、压力影响超临界二氧化碳物性进而影响超临界二氧化碳携岩速度,岩屑速度随着温度的升高而降低,随着压力的升高而升高.受偏心环空和重力的综合影响,岩屑在环空流动过程中产生了指进现象,宽间隙岩屑速度明显高于窄间隙岩屑速度;偏心度越大,宽窄间隙内岩屑速度分布差异越明显.在钻杆发生屈曲的窄间隙处岩屑体积分数急剧升高.通过地面设备,精确控制井底温度和压力、调节泵排量,采用钻杆扶正器,建议将偏心度控制在0.6以内,提高超临界二氧化碳钻井岩屑运移效率,为超临界二氧化碳钻井设计提供理论指导.

The technology of drilling with supercritical carbon dioxide can discover and protect reservoirs,improve ROP effectively and reduce costs,which has great advantages to exploiting unconventional oil and gas resources.Based on computational fluid dynamics theory,considering the physical properties of supercritical carbon dioxide,the cuttings velocity distribution laws are analyzed by the influence of temperature,pressure,drilling fluid velocity,drill pipe eccentricity and buckling.The calculation results show that cuttings velocity increases with the growth of pressure and decreases with the up of temperature.Influenced by eccentric annulus and cuttings weight,cuttings flowing in the annulus appear fingering phenomenon.Cuttings velocity in the wide gap is significantly higher than the narrow gap.The greater the degree of eccentricity,the more obvious of cuttings velocity distribution between the wide gap and narrow gap.When drill pipe buckling occurs,the cuttings volume fraction in the narrow gap increases dramatically.For improving cuttings transport efficiency of supercritical carbon dioxide drilling,it is necessary to use ground equipment to control the bottom hole temperature,pressure and to adjust pump displacement precisely.Applying drill pipe centralizer will dramatically improve the centering degree.Therefore,in order to guarantee cuttings transport efficiency,eccentricity is suggested to be controlled within 0.6.The analysis results can provide theoretical guidance for the design of supercritical carbon dioxide drilling.