一种快速计算溶解油气比的工程实用方法

天然气在原油中的溶解度是评价油气溶解性的重要参数之一,在工程上需查取图版而得到,结果不够准确、使用不太方便,不适于现场快速应用。为了便于在实际工程中快速准确地计算该参数,在雷萨特的模型上将美国石油协会相对密度与脱气原油摩尔质量的图版进行取点拟合成函数关系,结合原雷萨特关系式将其数学模型归纳推理得到一个新模型,只需要代入绝对压力、温度、脱气原油对水的相对密度以及天然气对空气的相对密度4个已知参数,通过计算机便可快速计算出溶解油气比。研究结果表明:①较之于雷萨特相关式,新模型简化了繁琐的迭代,不仅可以一步到位计算溶解油气比,而且还可以从公式中反映出各个参数是如何影响溶解油气比的;②油气比随着绝对压力的增大而增大、随着温度的增大而减小、随着脱气原油对水相对密度的增大先增大后减小、随着天然气对空气相对密度的增大而减小。结论认为,新模型可以快速、准确地计算出溶解油气比,其计算结果与原雷萨特模型符合度高;新方法提高了工程上计算溶解油气比的效率及准确性,可以推广使用。

A practical engineering model for quick calculation of solution gas oil ratios

The solubility of natural gas in crude oil is one of the important parameters of oil and gas solubility. In engineering, it can be obtained only from the chart, but the results are not accurate enough and this method is not convenient to use and not applicable for quick field application. In order to accurately and quickly calculate the solubility in the actual engineering, it is necessary to take points from the chart of API relative density and dead oil molar mass in the Lasater model and fit them into a functional relationship. Then, based on the original Lasater relation, a new model was derived from the mathematical model. So long as 4 known parameters (i.e., absolute pressure, temperature, relative density of dead oil to water and relative density of natural gas to air) are introduced into this new model, the solution gas oil ratio (GOR) can be calculated quickly by a computer. And the following research results were obtained. First, compared with Lasater relation, this new model simplifies the tedious iteration, and it can not only calculate the solution GOR in one step, but also reflect the effects of each parameter on the solution GOR in its formula. Second, the GOR increases with the increase of absolute pressure, decreases with the increase of temperature and relative density of natural gas to air, and increases firstly and then decreases with the increase of relative density of dead oil to water. In conclusion, this new model can accurately and quickly calculate the solution GOR and its calculation result is highly consistent with that of the Lasater model. In addition, this new method improves the calculation efficiency and accuracy of solution GORs in engineering, thus it is worth popularizing.