泡沫钻井液在井筒中的流动与传热

针对泡沫钻井液特殊物理性质，建立了泡沫在井筒中流动与传热的数学模型，并给出了模型求解方法。为了分析传热对泡沫钻井水力参数的影响，采用建立的数学模型和给出的求解方法进行的数值计算结果表明：钻杆内泡沫温度始终低于环空内泡沫温度和地层温度，而环空下部泡沫温度低于地层温度，在环空上部泡沫温度高于地层温度。随着井深、注液流量和注气流量的增加，环空下部泡沫温度与地层偏差增大。传热使井口泡沫质量增大、井底泡沫质量减小、井底压力增大、最小携岩流速减小、最小注气流量增大，降低了泡沫的稳定性和携岩能力。另外，对泡沫的密度、Fanning摩擦系数也有一定的影响；井筒传热对泡沫钻井水力参数有一定的影响，但不是很明显，可通过增加注气流量和井口回压来抵消传热对泡沫钻井水力参数的影响。

Wellbore flow and heat transfer of foam drilling fluid

Foam drilling fluid has some special physical properties. The mathematical model for foam flow and heat transfer in wellbore was established, and the solution method of the model was proposed. In order to analyze the effect of heat transfer on the hydraulic parameters of foam drilling, the numerical calculation was conducted by employing the established mathematical model and the corresponding solution method. The results indicated that the temperature of foam in drilling pipe was always lower than that of foam in annulus and formation. The foam temperature at the bottom of annulus was lower than formation temperature,but the foam temperature at the top of annulus was higher than formation temperature. The deviation between foam temperature at bottom of annulus and formation temperature increased with the increases of well depth, liquid injection rate and gas injection rate. The wellbore heat transfer could result in quantity increasing of foam at top of annulus, quality decreasing of foam at bottom of annulus, pressure increasing at bottom of annulus, the minimum sand carrying velocity decreasing and the minimum gas injection rate increasing. The wellbore heat transfer could decreased the foam stability and the sand carrying capacity of foam,and it also could affect the foam density and Fanning friction coefficient. Although, the wellbore heat transfer had a certain extent effect on hydraulic parameters of foam drilling, the effect was limited and could be counteracted by increasing gas injection rate and back pressure.