Using the extended finite element method for simulation of transient well leakage in multilayer aquifers

The extended finite element (XFEM) is applied to the problem of transient leakage from abandoned or free-flowing artesian wells in perforated aquifer-aquitard systems. To more accurately capture the singularities in potentiometric head at the wells, the standard linear finite element basis is locally augmented with asymptotic analytical solutions which enable more accurate calculations of leakage rates between aquifers. Highly accurate flux estimates are obtained without the need for higher mesh resolution near wells. Simulations are carried out to test both the accuracy and convergence properties of the XFEM implementation, and the XFEM results are compared to those of a high-resolution standard finite element model. It is seen that for the type of singularity-driven problem posed here, the standard FEM is unable to resolve leakage rates without very fine discretization, but that the XFEM performs robustly with fewer degrees of freedom. The impact of aquifer geometric heterogeneity on leakage rates is assessed and seen to be an important factor in determining total leakage. It is demonstrated that the XFEM may be a valuable tool in many water resources applications where small-scale effects can impact global system behavior.     

Analytical solution for two-phase flow in a wellbore using the drift-flux model

This paper presents analytical solutions for steady-state, compressible two-phase flow through a wellbore under isothermal conditions using the drift flux conceptual model. Although only applicable to highly idealized systems, the analytical solutions are useful for verifying numerical simulation capabilities that can handle much more complicated systems, and can be used in their own right for gaining insight about two-phase flow processes in wells. The analytical solutions are obtained by solving the mixture momentum equation of steady-state, two-phase flow with an assumption that the two phases are immiscible. These analytical solutions describe the steady-state behavior of two-phase flow in the wellbore, including profiles of phase saturation, phase velocities, and pressure gradients, as affected by the total mass flow rate, phase mass fraction, and drift velocity (i.e., the slip between two phases). Close matching between the analytical solutions and numerical solutions for a hypothetical CO₂ leakage problem as well as to field data from a CO₂ production well indicates that the analytical solution is capable of capturing the major features of steady-state two-phase flow through an open wellbore, and that the related assumptions and simplifications are justified for many actual systems. In addition, we demonstrate the utility of the analytical solution to evaluate how the bottomhole pressure in a well in which CO₂ is leaking upward responds to the mass flow rate of CO₂-water mixture.     

高密市激电测深定井方法探讨

在高密的找水工作中,采用激电测深法进行定井,推断含水层的位置和富水性,在物探确定的异常部位实施钻探,找水效果显著。根据高密市找水定井实例,简要介绍激电测深定井法在找水定井过程中应注意的事项,为今后运用该方法进行找水定井工作提供借鉴。     

注聚区油井砾石分级充填防砂工艺技术研究

注聚区油井砾石分级充填防砂工艺技术是针对胜利油田注聚区见聚油井产出液黏度增大、携砂能力增强,提液引效措施加剧油井出砂使油井防砂有效期变短等问题进行研究的。该技术是在注聚区油井充填防砂时改变过去采用单一粒径砾石进行充填防砂的做法,将不同粒径砾石按不同比例分级充填到近井、炮眼附近和筛套环空,同时在中粒度粒径的砾石中加入经过表面处理的短切纤维,提高了砾石充填挡砂屏障的挡砂强度,实现了挡砂屏障的“挡砂、稳砂、排砂”的功能。截止到2010年4月底,该技术现场累计推广应用32井次,分级充填后注聚区油井液量由27．2m3提高到40．43m3,油量由1．01m3提高到3．89m3,增幅分别达40％和80％,最长防砂有效期已达到400d。该技术的研发和应用,较好地解决了注聚区油井提液引效使防砂有效果变短和油井近井堵塞的问题,具有良好的应用前景。     

单基站CORS系统在胜利油区石油天然气井位测量中的应用

随着GPS技术的飞速前进,利用网络RTK技术建立的连续运行卫星定位系统已成为GPS应用的发展热点之一。通过对胜利油田单基站CORS系统的组成、功能及在胜利油区石油天然气井位测量中的应用方式及精度分析的论述,对单基站CORS系统在石油天然气井位测量中的现实意义和应用前景进行了展望。     

青海贵德地区DR1地热井井旁涌水原因分析 及处理工艺应用研究

地热资源属于清洁能源,主要通过地热井方式进行开发利用,成井工艺质量决定地热资源开发利用。贵德盆地DR1地热井由于成井时间较长,出现井旁涌水事故。本文详细分析了井旁涌水原因,采用合理方式成功处理涌水事故。为类似地热工程提供借鉴。     

The suitability of shallow hand dug wells for safe water provision in sub-Saharan Africa: Lessons from Ndola,Zambia

Many informal communities within urban areas in sub-Saharan Africa are heavily reliant on shallow hand-dug wells for water, but these are vulnerable to contamination from a range of sources. This paper assesses the heavy metal contamination and total coliform risk of unprotected shallow wells in Ndola, Zambia – a city struggling with contaminated surface waters from both bacteriological and potential mining waste products. One hundred and twenty three shallow wells were sampled across the Ndola, and these encompassed the three main lithologies of the city. All wells lacked an internal casing, however, some wells did have covers and/or pavements surrounding the wells, albeit of dubious efficacy. Despite the lack of protection, the quality of water used abstracted from these wells generally met the World Health (WHO) guidelines for heavy metals (with the exception of Al) and total coliforms (although, this was highly variable). The quality of shallow well water varied across Ndola relative to the underlying geology, where total recoverable concentrations were typically lowest in granite-gneiss. Dissolved load concentrations were lowest in dolomite-limestone, highlighting the role of aquifer geology in acting as a buffer against metal toxicity. Our study illustrates that shallow wells, within the appropriate geological units, may provide a safe and reliable source of drinking water. Well protection is, however, needed to ensure that the proliferation of shallow well use does not lead to regional degradation of the groundwater resource. There is an immediate need to invest in promoting internal well casing during the construction of shallow wells, concomitant with investment and education into protecting wells at the surface, despite the current relatively low level of contamination in wells without protection.     

UNSTEADY MOVEMENT OF FRESH WATER IN THICK UNCONFINED SALINE AQUIFERS

Abstract

Fresh-water lenses are formed in unconfined saline aquifers in response to deep percolation from rainfall, artificial recharge, and seepage from irrigation waters and/or in response to injecting fresh water through vertical or horizontal wells. An approximate differential equation is derived in terms of the depth of the fresh-salt water interface below the initial position of the saline-water table. This equation is analogous to that of the ground-water motion in two dimensions. The wealth of knowledge available from solving the latter equation is used to obtain approximate expressions for the movement of the fresh-salt water interface in several flow systems wherein this interface does not reach the bottom of the aquifer. These approximate solutions as well as others for related quantities of interest may afford useful tools for rationally planning the extraction of usable waters from such flow systems.     

Optimal pumping locations of skimming wells

Abstract

A real-life problem involving pumping of groundwater from a series of existing wells along a river flood plain underlain with geologically saline water is examined within a conceptual framework. Unplanned pumping results in upconing of saline water. Therefore, it is necessary to determine optimal locations of fixed capacity pumping wells in space and time from a set of pre-selected candidate wells that minimize total salinity concentration in space and time. The nonlinear, non-convex, combinatorial problem involving zero—one decision variables is solved in a simulation—optimization (S/O) framework. Optimization is accomplished by using simulated annealing (SA)—a search algorithm. The computational burden is primarily managed by replacing the numerical model with a surrogate simulator—artificial neural network (ANN). The computational burden is further reduced through intuitive algorithmic guidance. The model results suggest that the skimming wells must be operated from optimal locations such that they are staggered in space and time to obtain least saline water.     

地震沉积学在大庆长垣密井网条件下储层精细描述中的初步应用

文中针对大庆油田特高含水期精细调整挖潜,需要精细精确刻画储层的要求,充分利用大庆长垣油田密井网条件下储层精细描述成果及高密度三维地震资料,建立了处理-解释一体化高保真地震处理、大密度合成记录精细标定及地层切片优选方法;针对不同类型砂体分布特点,给出了利用地层切片采用"砂中找泥"和"泥中找砂"的单一河道识别分析方法,形成了"地震趋势为引导,井点相控"的井震结合储层精细刻画方法;实际应用证明对剩余油的分析认识更具针对性,应用点坝识别成果指导了D区水平井方案设计,取得了较好的钻遇效果。