超深层天然气藏开发基础理论研究

China has huge oil and gas reserves in the ultra-deep formation. However, at the high temperature, high pressure and high stress (HTHPHS) conditions, the engineering response of rock mechanics in reservoir and special formations, the multi-scale seepage mechanisms in the reservoir formation and the flow characteristics (with phase transition) in wellbore are extremely complex which may significantly affect the high efficiency development of the ultra-deep gas resource. In this project, targeting on the above critical challenges, by employing experiments / numerical simulation / theoretic analysis, the following key problems will be extensively studied: the characteristics of the rock mechanics, oil-gas-water phase transition and rheology and the multi-scale nonlinear seepage mechanism in reservoir when coupling the temperature field, pressure field, wellbore multiphase flow field, the seepage filed and the stress field; modeling of the borehole integrity at the reservoir and special formation, the sand production, the origin and expansion of complex fractures, the multiphase flow in wellbore and the multi-field coupled multi-scale nonlinear seepage; the regularities of the ultra-deep borehole instability, sand production, complex fractures origin and expansion, multi-components multi-phase flow and nonlinear seepage in ultra-deep reservoir formation. The critical theoretical bottleneck in ultra-deep gas development will be broken through. The basic theoretical system for the development of ultra-deep oil and gas reserve will be improved, which may provide strong theoretical support to the high quality high efficiency development of ultra-deep oil and gas resource.

我国超深层油气资源储量巨大，开发过程中在高温、高压、高应力作用下，储层及地层岩石力学工程响应复杂、储层多尺度渗流机理复杂、井筒产出流体存在相变以及多相流动复杂等问题，影响深部气藏高效开发。本项目针对以上关键问题，通过实验、数值模拟和理论分析，研究温度场、压力场、井筒多相流场、渗流场和应力场等多场耦合条件下地层的岩石力学特征，井筒中油、气、水相态与流变特征，油气层多尺度非线性渗流机理；建立储层及特殊复杂地层井筒完整性模型、油井出砂模型、复杂裂缝起裂扩展模型、井筒多相流动模型、储层多尺度非线性多场耦合渗流模型；揭示超深井井筒完整性失效规律、出砂规律和复杂裂缝扩展规律、超深井井筒多组分多相流动规律、超深储（气）层非线性渗流规律等。突破超深层天然气藏开发关键理论瓶颈，完善超深层油气藏开发的基础理论体系，为我国超深油气资源优质高效开发提供支撑。

在高温、高压、高应力作用下，超深层油气资源开发过程中存在储层及地层岩石力学工程响应复杂、储层多尺度渗流机理复杂、井筒产出流体相变及多相流动机理复杂等诸多复杂问题，影响深部气藏高效开发。. 针对上述科学和技术难题，通过实验、数值模拟和理论分析等研究手段，结合我国超深层天然气藏的环境条件和地质特征，揭示了高温、高压、高应力条件下岩石力学特性变化规律，构建了超深地层热-流-固耦合井筒完整性分析模型和产层出砂预测模型及复杂裂缝起裂扩展模型；厘清了开采过程中产出流体的相变和流变规律，提出了超深层凝析气藏流体的相态和物性的预测方法；揭示了超深地层高温高压多相流体在井筒中的流型转化机理和复杂流体多相流动特征，建立了高温高压高应力条件下的储层-井筒多场耦合多相流动模型和高温、高压、高应力下油气藏储层渗流场、岩石变形场的多场耦合流动模型，明确了油气藏多尺度多场耦合非线性渗流规律。. 研究结果表明：高温、高压、高应力条件下地层的出砂情况受储层岩性、生产压差、地应力非均质性、岩石胶结强度等因素影响显著；射孔方位及数量、压裂液温度、地应力状态等因素对水泥环应力分布影响较大。随温度升高，裂缝扩展时砂岩表面应力集中存在时间增长，无牵引裂缝开口位移逐渐减小。高温高压流体在超深层井筒中运移时，相变作用导致传统的气液“四流型”变为更复杂的气液和超临界“六流型”，在井筒中存在反凝析现象，相变点位置主要与井筒内流体温度和压力分布相关。天然气产量与储层孔隙度、裂缝渗透率、弹性模量和泊松比呈强正相关性，高弹性开采条件下，井生产早期为缝控阶段，产量高但迅速递减，后期为基质控制阶段，产量递减慢，应及时补充储层能量。通过以上研究成果的建立，完善了超深层油气藏开发的基础理论体系，为我国超深油气资源优质高效开发提供支撑。