Abstract:

Adoption of insulated tubing on the upper part of offshore production strings is an effective method to increase temperature of produced liquids and prevent wellbores from wax deposition. A scientific design for a proper depth of insulated tubing requires accurately predicting the temperature profile of offshore production wellbores. When produced liquids were regarded as a gas-liquid two-phase flow, equations for its mass conservation, momentum conservation and energy conservation could be, respectively, deduced. These equations integrate effects of temperature and pressure on thermophysical properties of oils, gases and formation waters as well as the effect of deviation angle on heat transfer and pressure drop with the internal heat resource caused by mechanical energy loss of an electric submersible pump. A numerical simulation method suitable for a coupling solution to temperature and pressure fields of offshore production wellbores was established using staggered grids and the fully-implicit finite-volume discrete technique, and this method offered a guarantee to make the solution of the model stable and convergent. The established model was applied to analyze temperatures of an offshore production wellbore and design the depth of its insulated tubing. The result shows that the prediction of the model is of high accuracy with a fractional error of 0.46%, and the designed depth of insulated tubing can effectively increase the temperature of oil fluids and prevent the wellbore from wax deposition.

Key words: temperature, pressure, insulated tubing, production well, offshore

摘要：

生产管柱上部采用真空隔热保温油管是海洋油井提高产液温度，防止油井结蜡的有效手段，科学设计保温油管的合理下深则需要准确预测海洋采油井筒温度剖面。将产液视作气液两相流，分别建立了质量守恒、动量守恒和能量守恒模型，模型中考虑了温度和压力对原油、天然气和地层水热物理性质的影响，井斜角对换热和压力降的影响，以及电潜泵机械能损失引起的热源。采用交错网格和全隐式有限体积法离散技术，建立了适合于海洋生产井筒温度场和压力场耦合求解的数值方法，保证了模型求解的稳定和收敛。利用所建立的模型对1口海洋油井进行了井筒温度分析和保温油管下深设计，结果表明，模型预测精度高（相对误差为0.46%），设计保温油管下深能有效地提高油流温度，避免油井结蜡。

关键词: 温度, 压力, 保温油管, 生产井, 海洋