海洋深水浅层钻井关键技术基础理论研究

Deep water has become an important potential area in the campaign of international oil and gas exploration and development in recent years, and the South China Sea is extremely rich in oil and gas resources specifically. Deepwater drilling is a key component of deepwater oil and gas exploration and development, which has the characteristics of high-cost, high-risk and high-tech. Currently deepwater drilling key technology is monopolized by a few foreign companies, meanwhile China's deepwater drilling started late, and should be put into research immediately as the basic theory remains underdeveloped. The major technical challenges of deepwater drilling start from the shallow seabed, among which are shallow geological disasters, sea temperature, shallow soft soil, long riser and subsea wellhead stability. The survey and experiment of this project are: deepwater drilling geological risk identification and evaluation method through simulation and experimental study of the mechanism of deepwater shallow geological disasters; subsea wellhead mechanical behavior pattern under riser's motion in deepwater environment via study of riser kinetics; deepwater conductor load analysis model and optimization design method through exploration of drilling - seabed soil disturbance law; calculation and control method of drilling fluid narrow density window of shallow layer through study of multiphase flow pattern under condition of shallow geological hazards. Eventually, the theoretical system of key technology of deepwater shallow layer drilling will be achieved, preparing the theoretical foundation for breakthroughs out of the bottlenecks of deepwater drilling technology.

近年来深水海域已成为国际上油气勘探开发的重要接替区，我国南海深水油气资源极为丰富。深水钻井是深水油气勘探开发的关键环节，具有高成本、高风险和高技术的特点。目前深水钻井关键技术被极少数外国公司垄断。我国深水钻井起步晚，相关基础理论薄弱，亟待加强。深水钻井的技术挑战关键在海底浅层，如浅层地质灾害、海底低温、浅层软土和岩土、窄密度窗口、长隔水管和水下井口稳定等。本项目拟通过开展深水浅层地质灾害形成机理及模拟实验研究，提出深水钻井浅层地质风险识别与评估新方法；开展隔水管动力学特征研究，揭示隔水管力学行为对水下井口动载作用规律；探索钻井对海底土扰动规律，建立深水钻井导管荷载分析模型，形成深水钻井导管优化设计方法；开展浅层气与天然气水合物耦合作用下井筒多相流流动规律研究，形成深水浅层窄安全密度窗口压力计算与控制方法。最终形成一套深水浅层钻井关键技术的理论体系，为突破深水钻井中的技术瓶颈奠定理论基础。

我国油气对外依存度2015年度首超过60%警戒线，并持续攀升至2018年的70.9％，国家能源安全形势严峻。南海油气资源丰富，约占我国油气总资源量的1/3，其中深水占比超过70%，号称“第二个波斯湾”，是我国能源供应的重要接替区。国外深水钻井事故统计表明，水下井口下沉、浅层地质灾害、井眼报废等60%事故来自“浅层”钻井。业内专家公认：浅层钻井顺利，相当于深水钻井成功了一大半。受水深、恶劣环境、浅层土质特性等因素影响，深水浅层钻井关键技术难题主要是：浅层地质灾害识别精度低；隔水管系统安全控制难度大；喷射法施工表层导管与土相互作用机理不清；深水钻井井筒压力预测难、控制难。本课题通过开展浅层气、浅水流声波室内模拟实验，揭示了浅层气和浅水流的声学特征，建立了浅层气和浅水流声波响应特征识别模型和定量分析模型，利用深水模拟实验装置，研究不同钻井液体系、压力条件下水合物相态变化规律，建立了水合物随钻识别方法。采用有限元分析的方法揭示了深水海况条件对隔水管力学行为特征影响机理和大尺寸内部管柱与隔水管相互作用规律，通过室内模拟试验分析了导管振动对周围土强度的影响规律，形成了水下井口稳定性控制方法。基于导管、海底土、水下井口三者相互作用关系，建立了海洋环境、钻完井动载作用下的导管力学模型，分析了喷射过程中导管周围土体应力场、位移场，利用数值模拟分析，揭示了导管与海底土相互作用的时间效应，建立了喷射过程中导管瞬时承载力计算模型，得到了海流、导管尺寸、水下井口载荷、浅层土特性等因素对导管出泥高度的影响规律，结合深水作业特点，建立了钻井导管入泥深度、结构尺寸和力学性能设计的理论模型，形成了深水钻井导管设计方法。基于对典型深水井井身结构和水下井口装置结构特点的分析，研究了深水井环空圈闭压力的来源和形成必要条件，分析了环空流体的热力学性能随温度的变化规律，建立了多环空作用下的温度-压力-体积平衡矩阵方程，推导出了自由段管柱和封固段套管的热位移函数求解方程，构建了井筒地层热固耦合作用下的单环空井段、双环空井段和三环空井段的环空温压预测模型，建立了深水井筒压力控制方法。该成果使我国跻身于世界深水钻井技术先进行列，支撑实现了我国海洋钻井从浅水到深水的重大跨越，为践行“一带一路”和海洋强国战略奠定了坚实基础。