蒸汽-气体协同驱替与重力泄油开采方法研究

The heat loss to overburden layer is inceasing as the steam chamber extends laterally in SAGD process,and the OSR is decreasing consequently. Butler suggested that SAGP with addition of uncondensable gas(<5mol% of steam injected) could reduce the heat loss and improve OSR because of the gas congregation at the top of the formation. However, conventional SAGD/SAGP is not fitable for thin reservoir,light oil reservoir and deep reservoir with high pressure because the distance between injection well and production well is usually 5-10m.Therefore, a new mehtod of steam and gas flooding and assisted gravity drainage is introduced, in which parralel and staggered upper injection wells and lower production wells are involved. The advantages of such combined method include flexible well pattern with longer distance bewteen injection well and production well,the GWR is 0-300 depending on the reservoir properties and well location, more rapid oil produciton, larger oil recovery and wide suitability. Based on PVT, IFT and rheology analysis of oil, steam and gas, and lab experimental simulation with sand packed model and reservoir numerical simulation, the EOR principles of combined flooding and gravity drainage by co-injection of steam and gas will be investigated, which mainly includes development of heating chamber, reduction of heat loss by gas congregation at the top of formation, synergistic effect of flooding and gravity drainage, and so on. Then the method of determination of well pattern and optimization of injection and production parameters such as GWR.

SAGD开采过程中，随着蒸汽腔的扩展，向上覆岩层的热损失不断增大、油汽比降低。Butler等提出在SAGD基础上，注入蒸汽和小于5mol%的非凝析气进行SAGP(Steam and Gas Push)开采时，气体在蒸汽腔上部聚集，减小向上覆岩层的热损失，提高油汽比。但是，常规SAGD/SAGP的注采井井距为一般5-10m，SAGP注入气体的气水比小于60，对薄层油藏、稀油油藏或高压油藏适应性差。为此，申请者提出一种蒸汽-气体协同驱替与重力泄油开采方法，注采井采用"大井距"平行非正对排列，气水比0-300，采油速度快、采收率高、适应范围广。本项目拟通过原油-蒸汽-气体体系PVT、界面张力和流变性及填砂模型实验模拟与数值模拟，深入研究蒸汽-气体协同驱替与重力泄油过程中加热腔扩展、气体聚集与减小热损失、"驱替"与"重力泄油"协同作用等机理，给出合理部署注采井和优化气水比等关键参数的方法。

SAGD开采时，随着蒸汽腔扩展，向上覆岩层热损失不断增大、油汽比降低。Butler等提出在注蒸汽同时注入小于5mol%的非凝析气进行SAGP开采，气体在蒸汽腔上部聚集，可减少向上覆岩层热损失，提高油汽比。但是，常规SAGD/SAGP注采井井距一般5m-10m，SAGP气水比小于60，对薄层油藏和高压油藏适应性差。为了解决常规SAGD存在的问题，本研究开展了蒸汽-气体协同驱替与重力泄油开采研究，首先测定了渤海稠油与气体体系的PVT、界面张力和流变性。采用可模拟油藏压力的大型填砂模型开展了SAGD、SAGP和SGFD实验模拟，研究了不同开采方式开采动态和加热腔扩展规律。通过油藏数值模拟，研究了不同开采方式开采动态、加热腔扩展规律及注采参数和油藏参数对开采效果的影响，优化了SGFD井位部署和注采参数。进而，综合实验和数值模拟结果，分析了SGFD加热腔扩展、气体聚集与减小热损失、“驱替”与“重力泄油”协同作用等机理，评价了SGFD对不同类型油藏的适应性。结果表明，SGFD方法较常规SAGD方法可提高采收率5%~15%，尤其对薄层油藏和厚度变化大油藏提高采收率效果好，具有很好的应用前景。