超高密度油基钻井液井筒循环温度场模型研究

Wellbore Circulating Temperature Field Model for Ultra-High Density Oil-Based Drilling Fluid

现有井底压力模型假设钻井液循环温度为地层温度,其计算结果存在较大误差。为了准确计算钻井液循环温度,基于固-液热传导能量与物质守恒定律,建立了油基钻井液井筒循环温度场模型。以准噶尔盆地南缘高探1井油基钻井液为例,采用多组分复合方程求取高密度油基钻井液的各项热物理参数,同时考虑窄间隙环空高速钻井液循环摩阻产生的内热源项,利用有限差分数值方法求解井筒-地层-流体系统内钻井液的循环温度模型。研究结果表明:钻井液循环温度的主要影响因素为钻井液排量和密度,钻井液排量变化表现出摩擦增热与循环冷却两种相反的热效应,当排量超过临界值后,高速流体摩擦内热源明显增加;钻井液的热物理参数与固相体积分数呈正相关,导致钻井液温度随密度增大而升高;高探1井的模型计算值与实测值误差极小,证明该模型具有合理性和适用性。研究结果可为井底当量密度的准确计算和井底压力的有效控制提供科学依据。

The existing bottomhole pressure models assume that the circulation temperature of drilling fluid is the formation temperature, which always leads to large errors in calculations. In order to calculate the drilling fluid circulation temperature accurately, a wellbore circulation temperature model of oil-based drilling fluid was established based on the law of solid-liquid heat transfer energy and mass conservation. Taking the oil-based drilling fluid in Well Gaotan 1 in the southern margin of Junggar Basin as an example, multicomponent composite equation was used to calculate the thermal physical parameters of oil-base drilling fluid with high density. Meanwhile, considering the internal heat source produced by high-speed fluid friction within narrow annulus, finite difference numerical method was used to establish the circulation temperature model of drilling fluid in wellbore-formation-fluid system. The results show that, drilling fluid flow rate and density are the two main factors influencing the circulation temperature of drilling fluid. The change of drilling fluid flow rate shows two opposite thermal effects of friction heating and circulation cooling. When the flow rate exceeds the threshold, the internal friction heat of high-speed fluid increases obviously. The thermophysical parameters of drilling fluid are positively correlated with solid content, which results in the increase of drilling fluid temperature with density. In this case study, the calculations are very close to the measurements, which proves the model is reasonable and applicable. The research results could provide a scientific basis for effective control of equivalent density and bottom hole pressure.