An analytical method of analysing the oscillatory pressure head measured at any depth in a well casing

When a slug test is conducted in a highly permeable aquifer, a shallow pressure transducer in the well casing produces an oscillatory pressure head that is representative of the water level fluctuation, whereas a deep pressure transducer in the well casing yields an oscillatory pressure head that is different from the water level change. Although the solutions for shallow and deep pressure head are different, it is found that the ratios of the subsequent extremity displacements are in an identical relationship (an extremity can be a maximum or a minimum in the oscillatory pressure head). Based on this relationship, an analytical data analysis method for the determination of the hydraulic conductivity is developed for both shallow and deep pressure transducer data. This analytical method is applied to the pressure head measured at different depths in the well casing of a well partially penetrating an unconfined coarse sand aquifer. Satisfactory results are obtained, validating the applicability of this analytical method for pressure transducer data at any depth in a well casing. Copyright © 2007 John Wiley & Sons, Ltd.     

Design, Installation, and Uses of Combination Ground Water and Gas Sampling Wells

Waste disposal sites with volatile organic compounds (VOCs) frequently contain contaminants that are present in both the ground water and vadose zone. Vertical sampling is useful where transport of VOCs in the vadose zone may effect ground water and where steep vertical gradients in chemical concentrations are anticipated. Designs for combination ground water and gas sampling wells place the tubing inside the casing with the sample port penetrating the casing for sampling. This physically interferes with pump or sampler placement. This paper describes a well design that combines a ground water well with gas sampling ports by attaching the gas sampling tubing and ports to the exterior of the casing. Placement of the tubing on the exterior of the casing allows exact definition of gas port depth, reduces physical interference between the various monitoring equipment, and allows simultaneous remediation and monitoring in a single well. The usefulness and versatility of this design was demonstrated at the Idaho National Engineering and Environmental Laboratory (INEEL) with the installation of seven wells with 53 gas ports, in a geologic formation consisting of deep basalt with sedimentary interbeds at depths from 7.2 to 178 m below land surface. The INEEL combination well design is easy to construct, install, and operate.     

Evaluation of formation pore pressure behind the casing using borehole gravity data

Reliable estimates of the fluid pressure in the pore space of rocks are critical for different aspects of petroleum exploration and production including injection operations and scenarios of water flooding. Numerous approaches are available for formation pore pressure evaluation, however, these measurements become a challenge inside a cased borehole, and a list of possible options is short: either the casing is to be perforated, or the production tubing needs to be disconnected to perform the pressure tests. We present a method for through-casing evaluation of formation pore pressure without shutting down production. We suggest equipping an observation well with a borehole gravimeter and acquiring time variations of the vertical component of the gravity field. Changes in gravity occur during gas production and are related to time variations of formation pore pressure. Gravity changes obtained in the observation well are supposed to be inverted for time-dependent formation pore pressure variations beyond the casing. Our results and recommendations are based on numerical modeling of pore pressure spatial distribution during gas field exploitation and relevant changes in borehole gravity. Benchmark models were elaborated in order to consider a dynamic process of pressure changes in time and space under conditions similar to those in the Medvezhye gas field (Russia). Different modeling scenarios are considered for early and late stages of gas field exploitation. The sensitivity analysis was performed to estimate quantitatively a sensitivity of borehole temporal gravity changes to variations in formation pore pressure behind the casing. Based on resolution analysis we justify the possibility to extract the gravity measurements directly related to changes in pore pressure from the total changes in the gravity field due to reservoir exploitation. The impact of pore pressure on the gravity field measured in boreholes during the water flooding is also evaluated, and obtained results are discussed.     

A Simple Pneumatic Device and Technique for Performing Rising Water Level Slug Tests

Transmissivity can be estimated by several well documented methods employing data from rising water level slug tests in wells. A very simple and relatively inexpensive system can be constructed to lower the water level in a well. Compressed air is injected through a sealed device called a well head manifold, which screws onto the casing top and contains an air pressure gauge, an air entry valve, a quick release valve and a multi-channel water level indicator or a pressure transducer. Either of the latter is lowered into the well prior to pressurization.
Compressed air is injected into the casing at a low rate through the manifold, depressing the water level a desired amount. After stabilization, the quick release valve is opened and the air pressure inside the casing is reduced to atmospheric pressure instantaneously; the water level then starts to rise. Successive elevations of the rising water level are determined with the indicator or transducer and their elapsed times from valve opening are recorded. Plots of water level recovery vs. time can then be used to estimate transmissivity by the published methods of Cooper, Bredehoeft and Papadopulos (1967), Ferris and Knowles (1954) and Hvorslev(1951).
All of the items used for construction, with the exception of the quick release valve, can be bought off the shelf. The valve can be easily constructed in a machine shop. The total cost of the device, exclusive of the transducer, should be less than $500.     

海原甘盐池地震观测井水位动态特征分析

影响因素及埋藏类型是地下水观测数据前兆分析的重要资料.通过海原甘盐池拉分盆地内两口地震水位观测井(GYC 和 GYCN 井)的气压、降雨与水位资料,综合分析水位变化的影响因素,并分别利用阶跃响应函数、频谱分析法、潮汐波群相位超前或滞后法分析地下水埋藏类型.结果表明:(1)气压和降雨是影响海原甘盐池两口地震观测井水位动态变化的主要因素.(2)GYC井地下水埋藏类型为混合水,与该井成井时的判定资料不一致(承压水),可能与其时间较长、长年失修、存在破损现象有关,或受地表水影响较大 ;GYCN 井地下水埋藏类型为承压水.该研究结果为该地区地震水位观测井的准入(退出)机制、今后观测井点的勘选等提供科学依据,对今后异常识别和震情跟踪具有重要意义.     

Casing Leakage in Monitoring Wells: Detection, Confirmation, and Prevention

A small but significant proportion of all existing monitoring wells may be affected by leakage through the casing, usually at joints. Casing leakage can render data obtained from a monitoring well unreliable. Anomalous water level, water quality, or isotope data from a particular well are an indication of possible leakage. The occurrence of a casing leak can be confirmed by means of a pressure test using water. The magnitude of the leakage flow can be estimated from the pressure test or from the observed head anomaly. Casing leaks can be largely prevented with adequate care during monitoring well installation, but the possibility that data may be affected by casing leaks should always be taken into account during hydrogeological investigations.     

华蓥山地区4口井水位潮汐动态特征研究

本文选择沿华蓥山断裂带分布的荣昌等4口观测井,利用Baytap-G潮汐分析方法,计算各井水位和气压及理论固体潮的潮汐振幅谱,比较其潮汐频谱差异,通过对主要潮汐分波振幅的回归计算定量分析各井水位受气压潮和固体潮影响的大小。基于对井水位正常动态的认识,选择各井水位潮汐的主要分波,对井水位长时序数据进行分析计算,提取水位潮汐响应特征参数(振幅比和相位差),进而探讨特征参数动态变化特征。最后对井水位受气压潮和固体潮影响的差异原因进行了初步探讨。结果表明,荣昌井水位主要受气压作用的影响,北碚、大足、南溪三口井水位受固体潮-气压潮综合作用的影响,而荣昌井水位只受气压潮影响可能与该井所处含水层裂隙发育且该井未下设止水套管有关;荣昌井P_1S_1K_1波和南溪井M_2波振幅比和相位差在几次大震后没有明显变化,说明地震波没有使井孔与含水层之间的水流交换发生显著变化,而北碚井和大足井M_2波振幅比和相位差分别在汶川和芦山地震时发生变化,反映了地震波的疏通影响。     

辽河盆地地下流体异常与岫岩MS5.6地震

分析了１９９９年１１月２９日岫岩Ｍｓ５．６地震前,辽河油田６口观测井的前兆异常特征,观测项目有水位、采液量、采气量及套管压力等。该次地震前６口井的观测资料均出现明显的趋势异常和短临前兆异常,辐且具有较好的同步性,异常形态表现为升－降－升型,抽水、注水、气压、温度等干扰因素对观测资料没有影响,异常是可信的。     

岫岩偏岭5．6级地震前辽河盆地地下流体映震特征

本文主要分析了1999年11月29日岫岩偏岭5．6级地震前,辽河盆地内7口观测井的前兆异常特征。观测项目有水位、采液量、采气量及套管压力等。这次地震前兆7口井的观测资料均出现明显的趋势异常和短临前兆异常,并且具有较好的同步性。异常形态多数表现为升－降－升型。油田抽水、注水、采油、采气及大气压、固体潮等干扰因素对观测资料没有影响,异常是真实可信的。     

Drill-Through Casing Driver Drilling Method for Construction of Monitoring Wells in Coarse, Unconsolidated Sediments

Hole stability problems occurring during construction of monitoring wells in coarse, unconsolidated alluvium can be overcome by using a drill-through casing driver mounted on a standard top-head drive rotary rig. Steel casing is driven contemporaneously with drilling, providing continuous hole stability. Samples of aquifer material and ground water can be taken at discrete depths as drilling proceeds. Monitoring well completion is accomplished by: (1) using the steel casing as an open-ended piezometer; (2) installing a telescoping well screen; (3) plugging the casing end and perforating desired intervals, (4) installing one or more smaller diameter wells, and then (5) pulling back the steel casing. Advantages of this drilling method include maintenance of hole stability during drilling and well completion, faster borehole construction time than traditional methods in coarse alluvial deposits and other poorly sorted formations, and collection of representative samples of the geologic formations and ground water; additionally, drilling fluids are not required.     

水井含水层系统与水位观测系统对固体潮与地震波的响应

本文把水井含水层系统和水位观测系统联系在一起综合进行讨论,从振动学理论推导出这两个系统的二自由度振动方程组。从这个方程组的一些可能的解讨论了这两个系统对地震波和固体潮响应的影响因素。 认为水井含水层系统与水位观测系统对固体潮与地震波的响应,主要取决于这两个系统的固有周期。 理论分析表明,对于地震波来说,含水层的导水系数越大,水井水柱的有效高度越大;观测仪器的等效质量越大,浮标截面圆半径越大;井管截面圆半径越小,则系统响应的放大倍数越大。但是,这些因素对于长周期固体潮响应的影响很小;并指出在某些情况下水位观测系统的周期可起重要作用,在研究分析中不应忽视。      

对扶余油田套管变形的几点看法

我们利用扶余油田的压裂资料,分析了该油田应力场的特点,探讨了油田套管变形的原因.认为该区以水平压应力作用为主.由于高压注水,有效法向应力降低,引起地层间的相对滑动,造成套管变形.主要的套管变形是由于地层沿水平间断面--AB 界面的滑动造成的.通过控制注入压力和注水方式可以降低 AB 界面中的空隙压力,使界面上的法向应力有所恢复,降低套管变形的速率.      

天津地区咸水层观测井的改造与优化问题讨论

本文系统清理、分析了天津地区的咸水井观测资料,通过实际观测资料分析认为,天津地区的咸水体具有封闭性好,不开采的优势,具备了作为地震观测井的基本条件;在观测资料的动态方面,一般具有两种动态变化特征,但仅个别井能够记录到微弱固体潮信息,同时也不能记录到水震波;在映震方面,取得了一批震例资料,其异常幅度往往较大,映震特征明显;在观测层的选取上,一般应选择50 m以下的咸水层,并且在观测段中最好应包括海相层;在观测点的位置方面,应选择较大断裂的交汇点、拐点以及端点部位或活动性较强的断裂上。     

Evaluation of Vertical Head Profiles in Water Production Wells during Pumping

In a recent field study, the performance of four production wells was evaluated. The intake of a vertical turbine test pump was set below the top of the screened interval of the wells due to anticipated drawdown. Water level sounding tubes were welded to the well casing at various depths in each well. Drawdown data collected at various depths were used to evaluate the vertical head distribution in the wells under various pumping stresses. A direct relationship was observed between the head loss and the location of the pump intake in the production wells. A vertical head profile developed, suggesting that the location of the pump intake controlled the location of water production from the aquifer. The head loss in the wells observed during pumping was directly proportional to well discharge and annulus size between the well casing and the vertical turbine pump shaft. The pressure differences that developed in the wells created increased drawdown in water level sounding tubes installed deep in the wells compared to the total drawdown observed in the production wells. Certain implications should be considered based on the evaluation of the data obtained from this study. Because water management decisions are made using well test data, the quality of the data is crucial. In instances where well performance is evaluated using water level data collected from water level sounding tubes that are located close to a pump intake (in this case deep in the well), it should be recognized that well performance could be underestimated.     

柱状多层准弹性介质中声压波形的数值计算与分析——声法测井理论研究（Ⅱ）

为逼近油井实际情况,本文处理圆柱状（任意）多层介质中弹性波的传播问题。采用与文[1]相同的物理模型和二维FFT算法,给出了任意层数柱状准弹性介质中全波声压波形的计算方法和程序。 对多种参数进行了声压波形的数值计算,考察了串槽对全波波形的影响,着重分析了两个胶结面串槽引起初至波的变化。结果表明,串槽导致套管滑行纵波幅度明显降低,固、流界面的反射波是影响串槽时初至波特征的一个重要机制。     

柱状多层准弹性介质中声压波形的数值计算与分析——声法测井理论研究（Ⅱ）

为逼近油井实际情况,本文处理圆柱状（任意）多层介质中弹性波的传播问题。采用与文[1]相同的物理模型和二维FFT算法,给出了任意层数柱状准弹性介质中全波声压波形的计算方法和程序。 对多种参数进行了声压波形的数值计算,考察了串槽对全波波形的影响,着重分析了两个胶结面串槽引起初至波的变化。结果表明,串槽导致套管滑行纵波幅度明显降低,固、流界面的反射波是影响串槽时初至波特征的一个重要机制。     

A theoretical assessment of casing storage effects when pump sampling a partially penetrating borehole

ABSTRACT

A borehole partially penetrating a confined aquifer and pumped at a constant rate is modelled, taking account of water stored within the casing of the borehole. A solution for drawdown in the Laplace transform domain is obtained. The proportion of aquifer water in well discharge is numerically evaluated, tabulated as a function of time and compared with results for a fully penetrating well. Modification of the fully penetrating well theory, for application to partially penetrating wells, was found to give comparable results to the more complete analysis for a partially penetrating well both at early and late times. A previous estimate of the time of pumping before sampling (t_s) to minimize casing storage effects, based on the fully penetrating well theory, was confirmed by the partially penetrating well analysis and in fact was shown to be a conservative estimate (or overestimate) of the pumping time required when sampling from a partially penetrating well.     

A closed form slug test theory for high permeability aquifers

We incorporate a linear estimate of casing friction into the analytical slug test theory of Springer and Gelhar (1991) for high permeability aquifers. The modified theory elucidates the influence of inertia and casing friction on consistent, closed form equations for the free surface, pressure, and velocity fluctuations for overdamped and underdamped conditions. A consistent, but small, correction for kinetic energy is included as well. A characteristic velocity linearizes the turbulent casing shear stress so that an analytical solution for attenuated, phase shifted pressure fluctuations fits a single parameter (damping frequency) to transducer data from any depth in the casing. Underdamped slug tests of 0.3, 0.6, and 1 m amplitudes at five transducer depths in a 5.1 cm diameter PVC well 21 m deep in the Plymouth-Carver Aquifer yield a consistent hydraulic conductivity of 1.5 x 10(-3) m/s. The Springer and Gelhar (1991) model underestimates the hydraulic conductivity for these tests by as much as 25% by improperly ascribing smooth turbulent casing friction to the aquifer. The match point normalization of Butler (1998) agrees with our fitted hydraulic conductivity, however, when friction is included in the damping frequency. Zurbuchen et al. (2002) use a numerical model to establish a similar sensitivity of hydraulic conductivity to nonlinear casing friction.     

井水温度微动态形成的水动力学机制研究

井水温度微动态观测越来越受到有关学者的关注，已成为我国地震地下流体动态观测的主测项之一。观测结果表明，无论是水温的正常动态还是震前的异常动态的形成，用传统的热传导或热对流机制难以给出合理解释。因此笔者根据观测到的事实、异常特征与同震效应等提出了水动力学机制，即含水层变形→含水层内孔隙压力变化→井－含水层系统内水流变化→井水温度的变化。     

Vertical Contaminant Profiling of Volatile Organic* in a Deep Fractured Basalt Aquifer

Volatile organic compounds delected in ground water from wells at Test Area North (TAN) at the Idaho National Engineering Laboratory (INEL) prompted RCRA facility investigations in 1989 and 1990 and a CERCLA-driven RI/FS in 1992. In order to address ground water treatment feasibility, one of the main objectives, of the 1992 remedial investigation was to determine the vertical extent of ground water contamination, where the principle contaminant, of concern is trichloroethylene (TCE). It was hypothesized that a sedimentary interbed at depth in the fractured basalt aquifer could be inhibiting vertical migration of contaminants to lower aquifers. Due to the high cost of drilling and installation of ground water monitoring wells at this facility (greater than $100,000 per well), a real time method was proposed for obtaining and analyzing ground water samples during drilling to allow accurate placement of well screens in zones of predicted VOC contamination. This method utilized an inflatable pump packer pressure transducer system interfaced with a datalogger and PC at land surface. This arrangement allowed for real lime monitoring of hydraulic head above and below the packer to detect leakage around the packer during pumping and enabled collection of head data during pumping for estimating hydrologic properties. Analytical results were obtained in about an hour from an on-site mobile laboratory equipped with a gas chromalograplvmass spectrometer (GC/MS). With the hydrologic and analytical results in hand, a decision was made to either complete the well or continue drilling to the next test zone. In almost every case, analytical results of ground water samples taken from the newly installed wells closely replicated the water quality of ground water samples obtained through the pump packer system.