超深层复合盐膏层非协调变形机制与控制方法研究

Rich oil and gas resources are located under deep salt formation in China. The degree and frequency of casing damage is serious during oil and gas drilling process. According to statistics, nearly 50% of casing damage occurred in the interfaces of the composite salt-gypsum formation. However, the phenomenon shows significant discrepancies with traditional design and protection theory of the composite salt-gypsum formation. Aiming at the engineering demand and technical problem of casing damage in the interface of the composite salt-gypsum formation, the research concentrates on the scientific problem of non-coordinated mechanical deformation of the composite salt-gypsum formation. The longitudinal stress prediction method is established through numerical simulation of structural mechanics from the perspective of salt structure evolution. The property of longitudinal and non-continuous stress can be revealed. The effects of composite salt composition and interfacial cementation on the interfacial deformation and failure are studied through the true triaxial simulation test of the composite salt-gypsum formation. The non-continuous and non-linear creep and damage model compatible with the composite salt-gypsum formation is established and the model can reveal the stress and deformation mechanism at different interface areas of the composite salt-gypsum formation under high temperature and high stress conditions. Combined with the deep geological and engineering conditions, the strength checking model of the composite salt-gypsum formation is established during the whole drilling and development life cycle. The main controlling factor of casing damage can be obtained and the reliable scientific basis can be provided for the engineering technology of wellbore integrity of the composite salt-gypsum formation.

我国深层盐下油气资源丰富，油气钻采过程盐下套管损坏程度与频度严重，据统计近50%套管损坏发生在复合盐膏层界面位置，这与传统的复合盐膏层套管设计与防护理论有重大出入。针对复合盐膏层界面套管损坏的工程需求与技术难题，围绕复合盐膏层非协调力学变形的科学问题，从盐构造演化角度出发，通过构造力学数值模拟，建立复合盐膏层纵向地应力预测方法，揭示复合盐膏层纵向非连续原地应力特征；通过复合盐膏层真三轴模拟试验，研究复合岩性成分、界面胶结等对界面变形、破坏的影响规律，建立适合复合盐膏层的Cosserat介质非连续非线性蠕变损伤模型，揭示高温高应力条件下复合盐膏层不同界面区域应力与变形机理；结合深层地质与工程情况，建立钻采全生命周期复合盐膏层套管强度校核模型，获得复合盐膏层套管损坏的主控因素，为复合盐膏层井筒完整性的工程技术提供可靠的科学依据。

我国深层盐下油气资源丰富，油气钻采过程盐下套管损坏程度与频度严重，据统计近50% 套管损坏发生在复合盐层界面位置，这与传统的复合盐层套管设计与防护理论有重大出入。针对复合盐层界面套管损坏的工程需求与技术难题，围绕复合盐层非协调力学变形的科学问题。本项目调研国内外盐膏层主要地区情况，建立20-200ºC范围内蠕变实验数据库。基于塔里木库车山前典型复合盐层为例，开展了常温及高温条件下盐膏岩蠕变力学实验，揭示了深层盐膏岩蠕变力学行为，建立了复合盐层非线性幂次律蠕变损伤模型，其中幂次n在1.0-2.0之间。开展了基于Kaiser效应测地应力的实验，建立了盐膏岩Kaiser效应测试方法。提出深层复合盐层的井周尺度的地质与工程一体化数值模拟方法；基于构造力学数值模拟，建立区块尺度的复合盐膏层纵向地应力预测新方法，揭示复合盐层纵向非连续原地应力特征，盐层内最大水平主应力减小，最小水平主应力增大，盐上层与盐层在最大和最小水平主应力方面会产生突变，而两层的应力差值会相差10-50MPa。基于数值模拟，考虑复合岩性成分、界面胶结等对界面变形、破坏的影响，揭示高温高应力条件下复合盐层不同界面区域应力与变形机理；结合深层地质与工程情况，建立钻采全生命周期复合盐层套管强度校核模型，该校核模型基于米塞斯强度准则。基于5MPa差应力条件下，套管在层间界面位置的应力差别为30-50MPa，当差应力提高则会加大套管内应力。获得复合盐膏层套管损坏的主控因素，其中包括地层倾角、地层弹性模量及泊松比以及地层蠕变规律，地层蠕变性以及持续作用时间会加剧套管内应力差异。该研究为复合盐膏层井筒完整性的工程技术提供可靠的科学依据。此外，本项目还揭示了复杂盐构造中脆性硬石膏储层包裹体沉降诱发小型地震的机制，并进行复杂盐构造附近孔隙储层水岩化学反应机理研究及沉淀计算等。该研究对于深层复合盐层井筒完整性、井壁稳定、井眼轨迹设计以及盐构造地质工程等提供了有利参考。