深水油气钻采井筒压力控制基础研究

Deepwater oil and gas are now becoming one of the most significant resources. The oil and gas reservoir in the South China Sea is considerably abundant. The deepwater petroleum development in China has just started and there are still some severe technical problems urgent to be solved such as complex formation pressure systems, narrow pressure window, low probability in keeping the oil-gas flow assurance and the control of annular pressure build up. Those problems mentioned above are all associated with particular environment temperature and pressure management in deepwater, thus we will focus on the pressure control based on the temperature condition during the whole process of deepwater oil and gas development. The following studies will be carried out: 1. Research on the complicated deepwater pressure systems of the South China Sea, to creat the precise predict method of deepwater formation pressure. 2. Research on flow patterns and pressure calculations of multiphase flow in deepwater wellbore, to establish the management pattern of varied gradient managed pressure drilling in deepwater. 3. Research on the mechanisms of sand & water control, gas hydrate plugging in high porosity and permeability formation, to form a guarantee method for long-term oil-gas flowing with high efficiency in deepwater. 4. Research on the evolution mechanism of annular trap pressure and the identification of ultimate safety limits, to establish the guarantee method of well integrity in production. Eventually a system of pressure control during the whole process of oil and gas production will be established, which provide the theory basis of the development of the deepwater oil and gas resources.

深水是未来国际油气资源争夺的主战场，我国南海深水油气资源极为丰富,是我国能源的重要接替区。目前，我国深水油气开发刚刚起步，面临着地层压力体系复杂、钻井安全密度窗口窄、油气长效流动保障困难和环空圈闭压力控制难等瓶颈问题，亟待攻关。这些问题都与深水特殊的温度与压力环境密切相关。本项目拟以温度载荷为约束、以压力控制为主线，开展以下研究：①南海深水多源多机制复杂地层压力体系研究，形成地层压力体系精确预测方法；②深水井筒多相流及相变条件下的流动规律与压力计算模型研究，建立深水变梯度控压钻井控制模式；③深水高孔高渗储层高效防砂控水与井筒水合物防控方法研究，建立深水油气长效流动保障机制；④深水井筒环空圈闭压力演变机理与安全控制方法研究，建立长期开采期间深水井筒完整性保障方法。最终形成一套深水油气钻采全寿命周期井筒压力控制理论体系，为突破我国目前深水油气钻采中的技术瓶颈奠定理论基础。

针对我国深水钻采过程中面临的地层压力体系复杂、钻井安全密度窗口窄、油气长效流动保障困难和环空圈闭压力控制难等瓶颈问题，本项目开展了系列研究，取得的研究成果包括：①揭示了底辟构造对超压形成与分布的影响机理，建立了基于机器学习算法的孔隙压力预测模型，提出了深水浅部无裂缝地层的呼吸效应新机理-地层渗透性机理，明确了单井及区域安全密度窗口的特征。②研制了井下新型分离器短节，开展了变梯度钻井室内模拟实验，验证了变梯度钻井的可行性，建立了正常钻井和气侵条件下的变梯度钻井井筒压力预测模型，形成了变梯度控压钻井关键参数优化设计方法。③建立了深水储层压裂过程中水力裂缝扩展模型和油气井生产段入流剖面模型，研究了井筒内水合物生成、生长、聚积和堵塞的动态过程，形成了集防砂、控水、水合物防治于一体的深水油气井长效流动保障控制机制。④研究了水泥环对环空圈闭压力的影响规律，提出了深水油气开采套管安全性评价和环空圈闭压力安全极限确定方法，形成了环空注氮气、预装破裂盘、优化套管参数等系列环空圈闭压力控制方法。研究成果为突破我国目前深水油气钻采中的技术瓶颈奠定理论基础。