Investigation Of Hybrid SAGD Using Carbon Dioxide, Propane, Nitrogen and Methane
本文研究了一种复合SAGD（蒸汽辅助重力泄油）工艺，该工艺利用四种气体溶剂，即二氧化碳、丙烷、氮气和甲烷，以5.0、7.5和10.0 wt%的不同浓度与蒸汽共同注入。目的是评估和比较甲烷、氮气和二氧化碳等不可冷凝气体与丙烷等可冷凝碳氢化合物的有效性；评价复合SAGD应用于枯竭低压油藏的效果；并对实验结果进行数值模拟，得到拟合后的相对渗透率曲线。为此，使用实验室尺度的圆柱岩心和一组平行水平注采井进行了严格的实验。并在此基础上，开发、模拟和校准了一个数值模型。 实验程序包括i）设计注入温度195°C和压力1.45 MPa（表压）下同时注入溶剂和蒸汽的系统；ii）设计用于收集采出液并测量各相流量分数的生产系统，同时确保平稳运行且生产压力变化最小；iii）设计用于精确控制加热器温度的控制系统。实验在等温条件下进行，模型渗透率和孔隙度分别为10.7达西和32%。 据观察，对于低压油藏，溶剂共注的采收率至少比单独使用蒸汽的采收率高18%。在同等重量百分比的基础上，发现甲烷是最好的溶剂，其最高采油率达到50.7%。与非凝结气体相比，丙烷的溶剂保留率最高，可达15%。在重油中溶解度较高的气体，如二氧化碳和丙烷，随着进料溶剂浓度的增加，石油采收率降低。 利用WinProp相态模拟软件包和STARS模拟器开开展了该过程数值模拟研究。对于效果较好的溶剂，通过调整相对渗透率曲线，拟合了油、水和天然气开采的实验室结果。由此得到的拟合模型能够预测复合SAGD过程中的油、水和天然气采收率，相对误差小于5%。
Abstract
This study investigates a hybrid SAGD (steam-assisted gravity drainage) process utilizing four gaseous solvents, namely, carbon dioxide, propane, nitrogen and methane that are co-injected with steam at different concentrations of 5.0, 7.5 and 10.0 wt%. The objectives are to evaluate and compare the effectiveness of non-condensable gases like methane, nitrogen and carbon dioxide with those of condensable hydrocarbons like propane; to evaluate the performance of hybrid SAGD applied to depleted, low-pressure oil reservoirs; and to numerically simulate the experimental results and obtain tuned relative permeability curves. For this purpose, rigorous experimentation is done using a laboratory-scale, cylindrical replica (i.e., physical model) of an oil reservoir with a set of parallel horizontal injection and production wells. A numerical process model is developed, simulated, and calibrated with the help of experimental data.
The experimental setup incorporates i) an injection system designed to co-inject solvent and steam at the required injection temperature of 195°C and pressure of 1.45 MPa, gauge; ii) a production system designed to collect the produced fluids and measure the fractional flow of each phase while ensuring smooth operation with minimal variations in production pressure; and iii) control systems designed to precisely control the heaters temperatures. The experiments are performed at isothermal conditions with model permeability and porosity, respectively, 10.7 Darcy and 32%.
It is observed that for low pressure reservoirs, oil recoveries with co-injected solvents are at least 18% more than that from steam alone. On an equal-weight-percentage basis, methane is found to be the best solvent, and results in the highest oil recovery of 50.7% of the original oil in place. Compared to non-condensable gases, propane has the highest solvent retention of up to 15%. The gases with higher solubility in heavy oil, like carbon dioxide and propane, show a reduction in oil recovery with an increase in feed solvent concentration.
A numerical model of the process is developed and simulated using Computer Modelling Group’s (CMG) WinProp and STARS simulators. For the solvents that are found to be promising, the simulated oil, water and gas recoveries are history-matched with their experimental counterparts by adjusting the relative permeability curves. The resulting, calibrated model is able to predict oil, water and gas recovery in the hybrid SAGD process with less than 5% relative error.
