加拿大M区块浅层油砂SAGD开采盖层稳定性研究

Study on Cap Rock Stability during SAGD Production in Shallow Oil Sand in Block M,Canada

高温条件下上覆盖层的稳定性及对注入蒸汽的有效封堵作用对于浅层油砂蒸汽辅助重力泄油(SAGD)的成功开发至关重要。为了在加拿大M区块应用SAGD技术时为开发方案设计与安全生产提供技术支撑,通过X射线衍射分析、CT扫描、稳态平板法与三轴应力测试,获取了该区块油砂盖层岩心的矿物组成、微观结构、热力学参数及岩石力学参数;利用小型水力压裂试验确定了油砂储层及盖层岩石的最小地应力与地层破裂压力梯度;采用油藏流体模拟与应力模拟耦合的方法,分析了SAGD开发过程中盖层的应力分布状态。试验与模拟结果表明:M区块油砂盖层岩心中黏土矿物含量较高,遇水可能发生膨胀,造成强度降低;盖层岩石没有裂隙或微裂缝,但存在弱面区,岩石物性表现出非均质性;盖层的最小主应力为3.65MPa,沿垂直方向,有利于对注入蒸汽进行有效封堵;整个开采生命期盖层的Mises应力最大值始终低于最小主应力,在设计的SAGD注汽温度与压力条件下,M区块油砂储层上覆盖层不会发生塑性形变或破坏,在整个生产期间能够保持密封的稳定性。研究形成的油砂SAGD开采盖层稳定性评价方法,为该类油藏热采注汽压力优化设计与矿场施工提供了理论依据。

The stability of overlying cap rock and its effective sealing to the injected steam under high temperature are crucial for the successful development of shallow oil sand with steam assisted gravity drainage(SAGD).The mineral composition,microstructure,thermodynamic parameters and rock mechanics parameters of the core from cap rock in the Block M,Canada were obtained by X-ray diffraction analysis,CT scanning,steady-state plate method and tri-axial stress test.A mini-fracturing test was used to define the minimum in-situ stress and the formation fracture pressure gradients of the oil sand reservoir and its cap rock.The stress distribution of cap rock during SAGD production was analyzed by coupling a numerical simulation of reservoir fluid dynamics with geomechanics.The experimental and simulation results show that the content of clay minerals in the core of cap rock is high,while the proportion of illite-montmorillonite mixed layer is as high as 35%.The core may expand when it contacts with water,resulting in a decrease in strength.The cap rock has no cracks or micro-cracks,but has a weak surface area,and exhibits heterogeneity in its petrophysical properties.The minimum principal stress(along vertical direction)of cap rock is 3.65 MPa,which is beneficial for the effective sealing of injected steam.During the entire lifecycle of production,the maximum Mises stress is always lower than the minimum principal stress of cap rock.Under the designed SAGD steam injection temperature and pressure,the overlying cap rock of oil sand reservoir in the Block M has not undergone plastic deformation or damage,and reliable sealing can be maintained throughout the production period.Based on the research results,a method was established to evaluate the cap rock stability of SAGD production of oil sand,and the research provides a technical reference for the optimization design and implementation of steam injection thermal recovery in such reservoirs.