深水环境下井壁失稳研究方法

发布时间：2018-02-24 14:17

本文关键词： 深水钻井高温地层浅部地层温度应力坍塌破裂压力　出处：《长江大学》2017年硕士论文　论文类型：学位论文

【摘要】：20世纪70年代末期,世界油气勘探开始涉足深水海域,近年来我国南海周边地区的深水油气勘探开发也在广泛地进行之中。向深水进军,开发我国深水油气资源已成为国内油气工业发展的必然趋势。然而深水钻井面临着特殊地质环境,浅部地层塑性强,井筒温压场复杂,钻井作业窗口窄,保持深水钻井井壁稳定是关系到深水钻井安全的关键。建立深水环境下井壁稳定评价方法,能为实现我国南海深水油气资源的高效安全开发提供理论依据。论文主要完成工作有:1.深水环境下孔隙压力预测孔隙压力预测一般基于有效应力原理,即其等于上覆岩层压力减去基岩有效应力。因此孔隙压力预测之前首先进行上覆岩层压力预测。在稳定的沉积速率下沉积物密度与埋深之间具有一定的数学关系,基于该原理国内外学者建立了多种深水环境下的地层密度模型,其中Power Law模型在深水环境下应用良好。其次以地震层速度为数据来源,以声波速度与基岩有效应力之间的正相关性为理论基础,建立了层速度预测孔隙压力方法。2.高温地层温度分布规律以地层导热基本理论和流体力学基本理论入手,根据热力学第一定律,在钻柱内、环空内、地层内、井壁围岩建立基本的温度场控制方程。以全隐式差分理论保证其离散的收敛性,有效割裂钻井液与地层之间的相互热交换,以进口钻井液初始温度首先建立井筒温度场,再建立井壁和地层温度场,有效地简化了温度场建立过程。3.井壁稳定分析针对于深水浅部塑性软泥岩地层,以塑性变形为基本假设,根据塑性破坏准则,结合力学平衡方程,进入超孔隙压力理论,建立软泥岩地层的破裂压力计算公式;针对井底井壁附加的温度应力对井壁的影响,以导热学和流体力学为基本理论,以热力学第一定律为基础,建立温度场控制方程,采用全隐式差分理论保证离散收敛,得到温度场分布。结合热力学平衡方程、井壁围岩应力-应变关系、协调方程后,得到井底附加温度应力,最终得到温降后的井壁坍塌、破裂压力,完成井壁稳定性研究。
[Abstract]:In the end of 1970s, world oil and gas exploration began to set foot in deep-water waters. In recent years, deep-water oil and gas exploration and development in the surrounding areas of the South China Sea are also being carried out extensively. Exploitation of deep-water oil and gas resources in China has become an inevitable trend in the development of domestic oil and gas industry. However, deep-water drilling is faced with special geological environment, strong plastic shallow formation, complex wellbore temperature and pressure field and narrow drilling window. The key to the safety of deep water drilling is to maintain the wellbore stability in deepwater drilling. It can provide a theoretical basis for the efficient and safe exploitation of deep-water oil and gas resources in the South China Sea. The main work accomplished in this paper is: 1.The prediction of pore pressure in deep-water environment is generally based on the effective stress principle. That is, it is equal to the overburden pressure minus the effective stress of the bedrock. Therefore, the overlying strata pressure is predicted first before the pore pressure prediction. There is a certain mathematical relationship between the sediment density and the buried depth at the stable deposition rate. Based on this principle, many kinds of stratigraphic density models in deep-water environment have been established by domestic and foreign scholars, among which Power Law model has been applied well in deep-water environment. Secondly, seismic layer velocity is taken as data source. Based on the positive correlation between acoustic velocity and effective stress of bedrock, the pore pressure prediction method of reservoir velocity is established. 2. The distribution of high temperature formation temperature is based on the basic theory of thermal conductivity and hydrodynamics. According to the first law of thermodynamics, the basic governing equations of temperature field are established in the drilling string, the annulus, the formation, the surrounding rock of the shaft wall. The discrete convergence is guaranteed by the fully implicit difference theory, and the heat exchange between the drilling fluid and the formation is effectively severed. First, the wellbore temperature field is established with the initial temperature of the imported drilling fluid, then the wellbore and formation temperature fields are established, which effectively simplifies the process of establishing the temperature field .3.The wellbore stability analysis is aimed at the deep water shallow plastic mudstone formation. Taking plastic deformation as the basic hypothesis, according to the plastic failure criterion, combining with the mechanical equilibrium equation and entering into the theory of excess pore pressure, the formula for calculating the fracture pressure of the mudstone formation is established, and the effect of the additional temperature stress on the borehole lining is discussed. Based on the basic theories of heat conduction and fluid mechanics and the first law of thermodynamics, the governing equation of temperature field is established. The discrete convergence is guaranteed by using the fully implicit difference theory, and the temperature field distribution is obtained. After the stress-strain relation of wall rock is coordinated, the additional temperature stress is obtained, and finally the wall collapse and fracture pressure after temperature drop are obtained, and the stability of wellbore is studied.
【学位授予单位】：长江大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TE21

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