Tracer Surveys Research Articles

Where has all the education gone in sub-Saharan Africa? employment and other outcomes among secondary school and university leavers

Anecdotal evidence and generalisations abound concerning the employment outcomes of secondary school and university leavers, but there is very little solid, accurate information on what these groups in African countries do after they have completed their education. Using tracer surveys, this paper presents comprehensive time-series information on the activity profiles of representative samples of secondary school leavers and university graduates in Malawi, Tanzania, Uganda, and Zimbabwe. The paper shows that much of the anecdotal evidence surrounding the labour market outcomes of these groups is spurious. While employment outcomes are generally much better than expected, the tracer surveys highlight the enormous challenges of educating and subsequently utilising secondary school leavers and university graduates in an efficient and effective manner in low-income African countries. In particular, given the paucity of new employment opportunities in the formal sector, much more needs to be done in order to ensure that both these groups are better prepared for productive self-employment, especially in high growth and higher skill activities.

Transient Eastern Mediterranean deep waters in response to the massive dense-water output of the Aegean Sea in the 1990s

We present a detailed account of the changing hydrography and the large-scale circulation of the deep waters of the Eastern Mediterranean (EMed) that resulted from the unique, high-volume influx of dense waters from the Aegean Sea during the 1990s, and of the changes within the Aegean that initiated the event, the so-called ‘Eastern Mediterranean Transient’ (EMT). The analysis uses repeated hydrographic and transient tracer surveys of the EMed in 1987, 1991, 1995, 1999, and 2001/2002, hydrographic time series in the southern Aegean and southern Adriatic Seas, and further scattered data. Aegean outflow averaged nearly 3 × 10 6 m 3 s −1 between mid-1992 and late 1994, and was largest during 1993, when south and west of Crete Aegean-influenced deep waters extended upwards to 400 m depth. EMT-related Aegean outflow prior to 1992, confined to the region around Crete and to ∼1800 m depth-wise, amounted to about 3% of the total outflow. Outflow after 1994 up to 2001/2002, derived from the increasing inventory of the tracer CFC-12, contributed ∼20% to the total, of ∼2.8 × 10 14 m 3. Densities in the southern Aegean Sea deep waters rose by 0.2 kg/m 3 between 1987 and 1993, and decreased more slowly thereafter. The Aegean waters delivered via the principal exit pathway in Kasos Strait, east of Crete, propagated westward along the Cretan slope, such that in 1995 the highest densities were observed in the Hellenic Trench west of Crete. Aegean-influenced waters also crossed the East Mediterranean Ridge south of Crete and from there expanded eastward into the southeastern Levantine Sea. Transfer into the Ionian mostly followed the Hellenic Trench, largely up to the trench’s northern end at about 37°N. From there the waters spread further west while mixing with the resident waters. Additional transfer occurred through the Herodotus Trough in the south. Levantine waters after 1994 consistently showed temperature–salinity (T–S) inversions in roughly 1000–1700 m depth, with amplitudes decreasing in time. The T–S distributions in the Ionian Sea were more diverse, one cause being added Aegean outflow of relatively lower density through the Antikithira Strait west of Crete. Spreading of the Aegean-influenced waters was quite swift, such that by early 1995 the entire EMed was affected. and strong mixing is indicated by near-linear T–S relationships observed in various places. Referenced to 2000 and 3000 dbar, the highest Aegean-generated densities observed during the event equaled those generated by Adriatic Sea outflow in the northern Ionian Sea prior to the EMT. A precarious balance between the two dense-water source areas is thus indicated. A feedback is proposed which helped triggering the change from a dominating Adriatic source to the Aegean source, but at the same time supported the previous long-year dominance of the Adriatic. The EMed deep waters will remain transient for decades to come.

Are groundwater inputs into river-dominated areas important? The Chao Phraya River - Gulf of Thailand

We used the natural geochemical tracers radon-222 and radium isotopes (223Ra, 224Ra, 226Ra, 228Ra) to assess exchange rates between the Chao Phraya River and the Gulf of Thailand, and the magnitude of groundwater discharge in the estuary. We performed tracer surveys during two periods in 2004, in January (dry season, gauged river discharge 47 m3 s21) and in July (wet season, 430 m3 s21). The isotopic data suggested that there are at least three different sources of these tracers in the estuary: river water, seawater, and groundwater. We estimated the extent of each input via a mixing model using 222Rn, 223Ra, and 224Ra activities and 224Ra : 223Ra ratios. Our analysis showed that the largest groundwater outflow occurs near the mouth of the river. Our groundwater discharge estimates based on the mixing model are 10 and 16 m3 s21 for January and July, respectively. An independent estimate of groundwater discharge in July using a mass balance of excess 226Ra together with our estimated water exchange rates based on 224Ra : 223Ra ratios resulted in a range of 14–19 m3 s21, depending upon the estimated amount of desorbable radium. Our estimated groundwater inputs therefore represent about 20% of the river flow during low flow in January and 4% during high flow conditions in July 2004. The unit shoreline flux (,200 m3 m21 d21 in July) for the area around the river mouth is over one order of magnitude higher than two other areas of the Gulf of Thailand where groundwater fluxes have been evaluated.

Jobs for the Boys? The employment experiences of secondary school‐leavers in Zimbabwe

This article discusses the main results of a comprehensive tracer survey of Form IV school‐leavers from urban and rural secondary schools in Zimbabwe during the mid‐to‐late 1980s. The principle finding of the survey is that the incidence of wage employment in early 1991 when the survey was undertaken was much higher than expected. Half of the 1985 school‐leavers were in some kind of wage employment. However, the employment experiences of males and females were markedly different, with 50 to 70 per cent of the males, but only 20 to 45 per cent of the females finding jobs.

A ‘lost generation’?: Key findings of a tracer survey of secondary school leavers in South Africa

Since the Soweto uprising in 1976, black youth in the townships of South Africa have been at the forefront of the struggle against apartheid. Organised political protest has taken a variety of forms including school boycotts, protest marches, work stayaways, and the destruction of school and other state property which invariably has led to violent confrontations with the police and security forces. An additional unintended consequence has been that gang violence linked to criminal activities has also become endemic in most townships. The effect of this political and social turmoil on township education has been quite devastating. Principals and teachers in the majority of secondary schools have lost control over highly politicised students who openly reject Bantu Education. Schools have been burned down or badly vandalised. Unable to continue their education, countless students have dropped out of school altogether. For those that remain, attendance is subject to constant disruptions. At many schools, students only come to school for a few hours a day. In terms of examination performance, matric pass rates among African school leavers have plummeted to around thirty percent. 1 Given the chaos of township life coupled with limited employment opportunities, it is commonly asserted that the urban youth who have grown up in South Africa since the Soweto uprising are a ‘lost generation’ who will, therefore, need massive assistance if they are to be integrated into post-apartheid society. Lost to whom or to what is never really made clear but the notion of a ‘lost generation’ is now deeply rooted in political and policy discourses in South Africa. What is however striking is that remarkably little is known about what black urban youth actually do once they leave school.2 In the absence of information of this kind, generalisations such as the ‘lost generation’ abound and before long gain the status of received wisdom. A well conceived national policy for youth in a democratic South Africa can only be formulated on the basis of comprehensive and detailed information about the kinds of activities young people engage in once they have left school. Education policy makers also need to assess the outcomes, both intended and unintended, of what is a costly and lengthy educational process. Only in this way is it possible to analyse the effectiveness of the education system in preparing youth for adult life and also to explore the complex relationships between education and the ‘world of work’. In both developed and developing countries, the tracer survey is the dominant methodology for collecting data on post-school activities and outcomes. Ideally, representative samples of all groups of school leavers should be traced and interviewed at regular intervals in order to derive detailed activity profiles over time. Despite the central importance of tracer surveys in research on the relationship between education and training and employment, it is surprising to find that only two nationwide tracer surveys of secondary school leavers in sub-Saharan Africa were undertaken during the 1980s in Botswana and Zimbabwe (Kann, 1991; Bennell and Ncube, 1993). This article presents the main findings of a tracer survey of over 1500 African school leavers from eight secondary schools located in townships in and around Johannesburg. The discussion is structured as follows. The first section provides some background information on the education system in South Africa. The second section then describes the methodology that was used to trace school

The tropical experiment of the Stratosphere‐Troposphere Exchange Project (STEP): Science objectives, operations, and summary findings

The Stratosphere‐Troposphere Exchange Project Tropical Experiment (STEP Tropical) investigated stratosphere‐troposphere exchange and dehydration processes in that region and season with the coldest average tropopause temperatures, the tropical western Pacific and northern Australia during the winter monsoon (January‐February) of 1987. This is also a period of extensive convective activity and rainfall. In addition to this primary goal, STEP Tropical (1) extended stratospheric aircraft chemical tracer surveys to the southern hemisphere subtropics and mid‐latitudes and (2) sampled the anticyclone that dominates the circulation over Australia in the lower stratosphere during the winter monsoon. Advanced fast‐response instruments on NASA's ER‐2 aircraft measured meteorological variables, stratospheric and tropospheric tracers, particles, and radiative fluxes. ER‐2 sorties included six ferry flight legs across the Pacific and eleven flights in the Australian region. The 1986–1987 monsoon was atypical in that (1) its date of onset, January 14, was 3 weeks later than normal and (2) it was unusually intense and sustained once it did arrive. As a consequence, almost all the flights were conducted under monsoon conditions, with only limited sampling of premonsoon and break‐monsoon continental convection. Illustrations show flight paths for each sortie on satellite images and on 100 hPa synoptic flow charts, as well as the timing of flights with respect to overall cloudiness in the Australian region. STEP Tropical results, reported in the accompanying set of papers, include (1) observational documentation of a convective scale cold trap that dries air of recent tropospheric origin to prevailing stratospheric minimum water vapor mixing ratios (3 ppmv or less); (2) indications that this drying mechanism can be effective not only in the anvils of the tallest clouds (which occur during “break‐monsoon” conditions) but also in the anvils of tropical cyclones and monsoon mesoscale convective systems; (3) demonstration that convectively generated gravity waves account for a significant part of the momentum forcing of the semiannual and quasi‐biennial oscillations in the stratosphere; and (4) documentation of an upper tropospheric source of NOy and a significant upward flux of NOy at the tropical tropopause. For monsoon convection to be an important contributor to the net transfer of tropospheric air to the stratosphere, a mechanism is required to move air from the cloud tops to significantly greater heights. STEP Tropical results suggest that gravity‐wave‐induced small‐scale turbulence or radiative heating of anvils provides this mechanism. Observational proof of the theoretically required high heating rates remains to be obtained.

Radioactive Steam Tracer Comparison Between Krypton-85, Xenon-133, NaI-131 (Methyl Alcohol Based), and NaI-131 (Water Based)

Summary Radioactive steam tracer surveys are run routinely in steam injection wells to check for tubing holes, packer leaks, open perforations, and steam migration behind casing. A field study comparing krypton-85, xenon-133, NaI-131 (methyl alcohol based), and NaI-131 (water based) was conducted to determine which radioactive tracers are the most accurate for these surveys. Testing showed that all tracers are accurate except NaI-131 (water based).

Direct Detection Of Water Flow Behind Pipe Using A Transient Oxygen Activation Technique

Abstract An indirect approach to determine if a formation is hydraulically isolated employs the cement bond or other acoustic logs to analyze the cement sheath. An a/ternate route to evaluate hydraulic isolation is to detect fluid movement directly. A new cased hole wireline service, the Water Flow Log (WFL *) detects induced radioactive water in the flow-channel to determine the axial movement of fluids near the wellbore. A solid state neutron source in a stationary logging tool is first turned on activating tile oxygen in the region near the wellbore, then turned off. If the oxygen is stationary, decay is exponential and predictable. However, if flow is present, axial fluid movement transports some of the temporarily activated atomic oxygen in the water past three detectors where gamma ray count rate transient responses are recorded. Analysis of the transients allows direct detection of the water flow in the annular space, a velocity measurement, and an estimate of the low magnitude. The WFL log has similarities to other wireline methods of directly detecting flow behind casing. Comparisons to audio logging, temperature profile logging, and radioactive logging reveal overlapping ranges of application. The WFL measurement uniquely has a wide range of application and retains sufficient resolution in circumstances where the other direct techniques are ambiguous. A constant flow interpretation model is introduced and tested with several field examples. The model allows a systematic evaluation of WFL data and has a format directly comparable to other logs. Introduction The Water Flow Log (WFL) directly detects water movement behind pipe by seeing activated oxygen in the moving water using the impulse activation technique(1). This allows the determination of water channeling in both producing and injection wells. Stationary measurements made with the tool in-between perforated zones and intervals of interest allow hydraulic isolation to be determined directly. Additionally, there are some special applications requiring a measurement of water flow between tubing and casing. A unique feature of the impulse activation technique is that a zero flow measurement is not required. A gamma ray count rate transient profile from one detector is used to detect water flow and measure velocity. Three separate detectors at different spacings provide sensitivity for a wide rate of conditions. The tool may be configured for either downward or upward water flow detection. Increased environmental sensitivity has placed a focus on containing disposed water in designated lithological formations, There are costs associated with unwanted co-production of water in oil and gas wells. Newer wells are drilled in reservoirs where hydraulic isolation over short intervals is a key requirement of the well design. Secondary and tertiary recovery schemes require hydraulic isolation between differing layers to function as designed. There are several wireline methods that provide data for evaluating hydraulic isolation. Temperature logs and radioactive tracer surveys are carried out in very much the same fashion as when they were first used. Acoustic cement bond logging techniques have evolved significantly since first run, but the underlying principles of the measurement remains the same.

Cement Evaluation - Past, Present, and Future

Introduction Cement evaluation began with the calculation of cement tops. This calculation assumed gauge holes and no channeling of the cement through the mud. Calipers were not available at that time. In the mid-1930's, the use of temperature surveys to determine in technical journals. Properly run temperatures journals. Properly run temperature surveys can identify the TOC, but distribution of cement-e.g., vertical isolation through zones of interest-is difficult to ascertain. Radioactive tracer surveys were run in the late 1930's to determine cement tops. Carnotite was mixed in the lead slurry and cement tops were determined with a gamma ray lot. Tracer surveys had the same limitations as temperature logs but were not time-sensitive. Ref. 1 includes an excellent bibliography. The acoustic cement bond log (CBL) appeared in the early 1960's and is still being run. The major limitation of the CBL is the difficult in identifying small channels. More recent developments in the field include attenuation-rate and pulseecho tools. A newer tool that is be coming more available in the field is the Segmented Bond Tool (SBT). This tool evaluates circumferential bond over the full 360deg. circumference in 60deg. segments. Another tool the Micro CBL, that would evaluate circumferential bond in eight 50deg. segments was under development, but has been discontinued because of the success of the SBT. Another new cement evaluation tool, the Ultrasonic Imager, is in the field-testing stage. Examples of these acoustic circumferential cement bond tools are presented later. Future developments may include more sophisticated tools, such as the cement volumetric scan tool. Each logging technique currently in use has limitations. Temperature Logs Temperature logs have been used to detect the TOC for many years. The most critical factor in the evaluation technique is the timing of the survey. Heat from the exothermic reaction as cement sets dissipates rapidly. Laboratory tests indicate a return to near normal temperatures in 24 hours. Early surveys also showed the effects of time, bottomhole temperature, circulating time, and thermal conductivity of the surrounding formations on the temperature profile. The temperature log remains an economical and effective way to determine the TOC and in tervals of larger cement accumulation. It is not a direct measure of vertical isolation across hydrocarbon-bearing zones; however, if a four-arm caliper is available, it is possible to infer good cement displacement if the TOC agrees closely with the calculated top (and full returns were present during pumping and displacement of cement). Fig. 1A shows a TOC temperature log. The local temperature profile must be known to avoid mistaking a change in the thermal conductivity of the formation for a cement top. Fig. 1B is a survey run to determine the TOC in a deepwater well. The base survey run at the end of the openhole log runs made interpretation possible. Fig. 1C is from a foam cement job. The temperature peaks marked "A" indicate fracture zones filled with cement. Note the hole enlargement indicated on the caliper curve in possible fracture intervals. Temperature logs, followed by a CBL are recommended on all foam cement evaluations. Data in the literature indicate that the optimum time to run the temperature log may precede the optimum time for the CBL by several hours or more. Compressive strength development lags behind the exothermic reaction as cement sets. It should be possible to record a temperature log and the CBL on tape and play the temperature and amplitude curves back with an openhole caliper curve on a compressed depth scale. This procedure facilitates cement evaluation in foam cement jobs and in conventional cement jobs in fractured formation areas. The temperature log is still useful in cement evaluation, particularly in foam cement evaluation and in combination with other tools. The tool cannot accurately delineate vertical isolation when run alone. Other tools were developed to fulfill this need. JPT P. 132⁁

Training for self-employment?: The performance of rural training centres in Zimbabwe

This article presents the results of recently completed research which assesses the extent to which post-school, pre-employment training initiatives in Zimbabwe have achieved their central objective of promoting rural self-employment. Past outputs from two government and one NGO training centres were successfully traced using conventional tracer survey techniques.

Fracture Stimulation In The Glisp Tar Sands Pilot-Case History

Abstract This paper reviews fracture stimulation of the McMurray formation in the Gregoire Lake In Situ Steam Pilot Project (GLISP), in northeastern Alberta. The purpose of the stimulations was to effect interwell communication between the injection and production wells prior to steam injection. In situ stresses measured at shallow reservoir depths, indicated a possibilityfor horizontal fractures, a very desirable prerequisite/or the potential success of the experimental pilot. Analyses of data collected during and following the final fracture stimulation in the pilot area on the I-I central injection well (i.e. tiltmeter data, bottomhole pressures, temperature profiles, tracer surveys, production response, laboratory experience, field observations) and fracture theory indicate that a very complex fracture geometry resulted with both horizontal and vertical components. These data were used to address an array of nine possible fracture geometries to determine the more probable fracture configurations). Interwell communication by hydraulic fracturing was achieved over short distances but not over the full well spacing of the pilot. Introduction Amoco Canada Petroleum Company Ltd., Petro-Canada, Inc., and the Alberta Oil Sands Technology and Research Authority (AOSTRA) are participants in an in situ experimental recovery pilot to investigate the feasibility of producing the heavy oil reserves in the McMurray formation in the Gregoire Lake area of the Athabasca tar sands deposit. This pilot known asthe Gregoire Lake In-Situ Steam Pilot or "GLISP" is located as shown in Figure 1. The pilot area, shown in Figure 2, was selected on the stratigraphy seen in the C-l abandoned core hole as being the preferred lithology in the general area. Three confirmation wells (D-l, D-2 and P-l) were drilled. Log evaluation indicated that the P-l well had the most suitable reservoir properties and therefore it was selected as the central injection well for the pilot. One observation well (O-1) was drilled and three producing wells were planned to be drilled triangularly spaced around this injection well (see original pilot configuration, Fig. 2). Drilling the three production wells was deferred pending the possible fracture stimulation of the central injection well. In addition, a tiltmeter survey was planned to monitor fracture evolution and better define the optimum locations for the wells. Injectivity tests run on the three confirmation wells indicated that fracturing would be required to accomplish communication between wells. Concurrent with the injectivity tests, in situ stress tests were also conducted to obtain fracture design data. The majority of these stress tests indicated closure pressures approximating the overburden pressure. In some tests there was also evidence of a much lower closure pressure. These data suggested the strong possibility of a horizontal fracture which would be preferred for the pilot. However, there was the distinct possibility of a vertical fracture, or more likely, a complex fracture geometry with both horizontal and vertical components. The P-l central injector was fracture stimulated through perforations at the base of the McMurray formation.

Hydraulic fracture evaluation with multiple radioactive tracers

For many years, wireline tracer surveys have been used to determine the height of fractures created during hydraulic stimulation procedures. A recent advancement in fracture evaluation technology has been to tag different stages of a fracture operation with multiple radioactive tracers, providing the capability to discern between created and propped fracture heights in one or more zones of interest. In this research, a wireline instrumentation and data analysis system is implemented to identify and separate the individual yields from multiple radioactive tracers, with an additional feature that determines whether the tracer material is inside of the borehole or distributed throughout the created fracture zone. A single postfracture pass of the logging instrument is used to accumulate gamma ray spectra at each 7.6 cm interval along a borehole. A weighted least‐squares spectrum unfolding algorithm calculates the radioactive intensities as a function of depth, while the peak‐to‐Compton down‐scatter ratio determines the proximity of the tracer material to the wellbore. Field examples illustrate the effectiveness of the system for the evaluation of multistage fracture operations.

Transient tracers as a problem in control theory

The problem of interpreting transient tracer surveys in the ocean is formally identified as corresponding to placing a “terminal constraint” on a “distributed system boundary control problem.” The mathematics available in control theory can then be brought to bear on the tracer data. Some of control theory is reviewed in the context of a simple tracer example to isolate the major issues. To use a transient tracer to invert for flow and mixing rates involves a two‐step process: start with an initial model, found independently, and determine if acceptable boundary conditions drive the model to reproduce the interior transient tracer at the observation times. If the model succeeds in that reproduction, one stops; the model is adequate and need not be changed. Only if this test fails does one obtain constraints on the fluid flow and mixing, which can be invoked in parameter estimation techniques of control theory. Terminal constraint observations can also be used to estimate the tracer concentrations at earlier times using a smoothing filter.

Geology of North Part of Corsicana Shallow Oil Field, Ellis and Navarro Counties, Texas: ABSTRACT

Oil was discovered at Corsicana, Texas, in 1894 during the drilling of a city water well. The boom which followed led to the development of the first commercial rotary method of drilling, the use of gas engines to pump wells, and the first regulatory efforts of oil and gas by the state of Texas. Two other booms occurred in the early 1950s and late 1970s because of waterflooding and an increase in the price of oil. Corsicana Shallow field consists of four producing horizons: Durango Sand, Wolfe City Sand, Pecan Gap Chalk, and Nacatoch Sand. The northern part of the field produces from the Wolfe City Sand of Campanian age within the Taylor Group. The sand can be divided into separate sand zones with independent oil-water contracts. As the sand zones are traced north and west, each thins and grades into shale. Corsicana field is located on the western edge of the East Texas embayment between the Balcones and Mexia-Talco fault zones. In the north part of the field, two fault trends are present, a N5°W up-to-the-coast fault zone and a N55°E trend of both up-to-the-coast and down-to-the-coast faults. Displacement along major faults ranges from 50 to 140 ft at the Wolfe City horizon. Product on techniques varied in Corsicana field with most wells being completed open hole with 2-in. tubing used for casing during the early 1950s. After 1959, most wells were completed by perforating through casing and mechanically fracturing the pay sand. New production techniques employed in the early 1980s involved the use of salt-water mud systems, selective perforating and treating of individual sand zones, and cement bond logs and radioactive tracer surveys. A polymer injection project in progress southeast of the city of Corsicana may provide additional means of oil recovery if the pilot project proves successful. End_of_Article - Last_Page 145------------

Leroy Storage Facility, Uinta County, Wyoming: A Case History of Attempted Gas-Migration Control

Summary Leroy gas storage facility, an aquifer storage development by Mountain Fuel Supply Co. in Uinta County (WY), is presented as a case history. This field represents a complex problem in aquifer storage because of the uncontrolled migration of gas to the surface. Considerable effort in reservoir engineering and planning has resulted in apparent and probable arrest of uncontrolled gas migration, although more time will be needed to evaluate and monitor the results of recent efforts. Incorporated in the evaluation of the leakage problem has been updated geological information, location and correction of possible well problems, computer simulation, extensive logging, tracer surveys, surface monitoring, and related engineering evaluation. A computer program developed to simulate a unique history match, including the effect of a time- and pressure-dependent leak, and a comprehensive analysis of data leading to the possible control of the leak by proper operating storage pressures are described. Introduction Through continuous attention from the Reservoir Engineering Dept. and support by management, the operations have continued with reduced scope and it now appears that the quantity migrating away from the storage horizon is definitely decreasing This paper briefly documents the history and presents the status of the storage field, relating efforts to isolate and control the leakage. The geography, geology, historical background, reservoir description, reservoir performance, and related engineering studies relevant to the case history are included. The computer simulation of history match including the leak, analysis of the results, subsequent reservoir engineering work, discussion of results, and conclusions are presented. Background The Leroy gas storage field is located in Uinta County (WY) in Township 16 North, Range 117 West. The field lies 80 miles [129 km] west of Rock Springs, WY, and approximately 100 miles [161 km] northeast of Salt Lake City. UT. This particular location was of interest to Mountain Fuel Supply Co. because it was favorably located relative to the pipeline supplying Salt Lake City. Interest in this area for prospective storage facilities dates back to 1969. Evaluation of data obtained from exploratory Leroy Well 3, originally drilled by the Shell Oil Co. in Summer 1951, suggested two potential storage formations-the Nugget and the Thaynes. The Nugget sandstone was rejected because of the questionable integrity of the caprock, the faulted structure, and abnormally high-pressure gradient. Testing of the Thaynes formation in Leroy Well 3 began in Oct. 1970 following re-entry and deepening to 3,135 ft [956 m]. An extended flow test was run, producing 4,000 to 8,700 B/D [636 to 1383 m /d] water with an initial gradient of 0.508 psi/ft [11.4 kPa/m]. Initial test evaluation indicated excellent transmissibility and an expanded drilling/reentry program followed. Leroy Wells 4, 5, and 6 were drilled and completed by Mountain Fuel Supply Co. in 1971. Leroy Wells 1 and 2 were also re-entered and completed as pressure observation wells. Interference and caprock integrity tests were conducted concurrently with the re-entry and dulling programs. During initial development, lost-circulation problems occurred while the Nugget sandstone was drilled across with water-base mud. This problem was alleviated by allowing the Nugget water to flow to the surface during drilling and an intermediate string of casing was run when the underlying Ankareh formation was encountered. Two potential horizons were initially considered for storage in the Thaynes formation, designated as the T-10 (upper horizon) and the T-20 (lower horizon). Preliminary testing with gas injection into the T-20 zone showed direct communication with the T-10 zone. Subsequent injection into the T-10 zone suggested favorable conditions for development. Wells 7, 8, and 9 were completed by Aug. 1971, and 2.0 Bcf [0.06 × 10 m ] of gas had been injected. Upon completion of the surface facilities, application was made to the Federal Power Commission (FPC) to begin storage operations. The application was approved Nov. 17, 1972. Following FPC approval, storage operations proceeded for the 1972–73 heating season. The following year, inventory had been increased to 3.5 Bcf [9 × 10 m ] and Wells 9 and 10 were completed as injection/withdrawal wells. JPT P. 132^

Secondary school leavers and the labour market in Swaziland

Secondary education in Swaziland has rapidly expanded in the decade or so since independence. Alongside this achievement has been a growing apprehension that the modern sector's capacity to generate employment is not commensurate with the rising number of educated young people leaving secondary school. The emergence of a ‘school leaver problem’ as disenchanted educated youngsters remained unemployed was therefore seen as a real possibility towards the end of the 1970s. Such considerations formed the backcloth to tracer surveys conducted in 1979 which investigated the post-school experience of secondary school leavers who left school in the period 1973–1977. Some aspects of these surveys are discussed in this article which covers the experience of school leavers in finding out about jobs and training, waiting time for jobs, and estimates of unemployment. The occupations entered by school leavers are then assessed in relation to demand projections for educated manpower. These observations reveal that institutional arrangements for transferring school leavers from school to work are embryonic and for a large minority of leavers family and other influentiaal contacts are more important than qualifications in securing a job. For Form 3 Junior Secondary School leavers some credence may be given to the popular impression that unemployment is worsening but Form 5 High School leavers are experiencing little difficulty as yet in finding work. More tentatively it would appear that the marginal additions to the skilled labour force stemming from school leavers are not modifying the occupational structure in line with recent manpower projections.

Logging Method for Determining Horizontal Velocity of Water in Oilfield Formations

A new borehole measurement technique has been developed for determining horizontal velocity of waterflowing in a reservoir. Neutrons are used to make a radioactive sodium tracer in formation salt water streaming around an unperforated cased observation well. Monitoring of gamma rays from the tracer provides data from which the horizontal velocity can be calibrated. Introduction In the enhanced recovery of oil, many techniques employ the injection of water or chemical solutions into the reservoir formations. To flood the reservoir effectively, horizontal continuity must exist between injection and producing wells, and good vertical conformance of the injected fluids must be maintained.Intervals inferred to be correlative from log data may be separated from one well to the next by reduced permeability caused by natural factors such as formation tensing, shale barriers, or faults. Reduced permeability also can be caused by factors resulting from production operations, such as migrating fines, swelling clays, emulsion blocking, scale and paraffin deposition, and sand production.Conversely, situations can arise where a zone may carry away excessive injection fluids. Such thief zones can be caused by channeling into adjacent beds or by fractures in the reservoir. When planning the injection of costly chemicals into a recovery pattern, it is essential to determine the magnitude of the problems well in advance. problems well in advance. Radioactive injection surveys, well-to-well pressure testing, and chemical tracer surveys can pressure testing, and chemical tracer surveys can provide useful data. These techniques are somewhat provide useful data. These techniques are somewhat qualitative in layered reservoirs and, in the case of tracer surveys, can require several weeks to obtain definitive results. Consequently, there is a need for a system to measure specifically the horizontal flow of water in selected zones of a reservoir.To meet this objective, a new nuclear logging technique for measuring horizontal water velocity in cased-off formations has been developed and field tested. At present, the system is limited to station measurements in the borehole. A radioactive tracer, sodium-24, is manufactured within the formation salt water by neutron irradiation. Over a period of time the radioactive tracer is monitored as it drifts away from the borehole. From these data, the horizontal water velocity is computed. Method and Theory Fluid now velocities in a typical reservoir range from about 0.1 to 1.0 ft/D (0.03 to 0. m/d). In some pilot projects, a monitor well close to an injector can have projects, a monitor well close to an injector can have fluids passing at several meters per day. In our method to measure the horizontal velocity, an unperforated cased borehole penetrating the formation of interest is used, since undisturbed streamline flow around the borehole is required.Neutron irradiation of a reservoir formation produces several radioactive isotopes that emit produces several radioactive isotopes that emit gamma rays with characteristic energies. Some of these are listed in Table 1. JPT P. 675

A Neutron Logging Method for Locating the Top of Cement Behind Borehole Casing

Introduction A few methods are known in the oil industry for determining the top of cement in the annulus around a casing. Before the advent of electrologging surveys, inflow and circulation methods provided information on the quality of cementation jobs. Temperature logging is presently the technique commonly used for this purpose. The radioactive tracer survey and sonic log based on the principle of "cycle skipping" also have been used principle of "cycle skipping" also have been used advantageously in selected cases. These surveys indicate only the presence or absence of cement. The cement bond log, however, gives additional information with respect to the bonding of cement to the casing. Grosmangin et al. have given a comprehensive account for analyzing the quality of cementation using the cement bond log. A new technique is proposed in this paper for locating the top of cement behind the casing using a neutron log. This method was used successfully in a North Kadi well in the Cambay basin, India, where temperature survey control was inadequate and the services of a cement bond tool were not available. Discussion The neutron curve responds primarily to the amount of hydrogen present in the borehole fluid and the fluid in the pores of the rocks. The neutron log is also sensitive to the pores of the rocks. The neutron log is also sensitive to the casing, cement sheath, and borehole diameter. However, the borehole effect is reduced considerably in the SNP log. Better results are achieved with the CNL log, where the effects of mud column, mud cake, rugosity, and even casing and cement are reduced considerably . On a neutron curve, the top of the fluid in a well is indicated by a "right-hand shift" in the neutron diagram. This is known as a fluid shift in the neutron log. As the neutron device is continuously pulled up hole, the device records the hydrogen content of the rocks of the wellbore and borehole fluids. Of these two fluids, the borehole fluid is more effective in slowing down the fast-moving neutron. Consequently, the intensity of the secondary gamma ray is reduced. As the tool is pulled farther up, there is an abrupt increase in the secondary gamma ray radiation on leaving the borehole fluid. This gives rise to the fluid shift on the neutron curve. Based on this principle, an anomaly is expected on the neutron log at the principle, an anomaly is expected on the neutron log at the interface of set cement and the overlying fluid zone in a cemented casing. The geometry of the cemented casing comprises a cemented and an overlying cement-free fluid zone sandwiched between the casing and the wellbore. As the neutron device is pulled up in a borehole against the cemented zone, the borehole fluid has little influence on the recording of the log. The effect of the fluid inside the pipe is insignificant on the neutron log because it is the common fluid against both the cemented and cement-free columns in the annulus. As the tool moves up into the fluid column overlying the set-cement zone, the borehole fluid slows down the fast-moving neutrons and reduces the secondary gamma ray intensity, giving rise to a "left-hand shift" on the neutron curve. The neutron log in Fig. 1 was recorded with an uncompensated neutron tool in a North Kadi exploratory well. In this well, the temperature survey did not indicate conclusively the quality of cementation against the pay zone. The cement bond log could not be recorded because the tool was not available. Under these circumstances, a neutron log was planned to check the quality of cementation. In this well, a shift is indicated in the neutron curve recorded after the production-casing cementation at 840 m. This shift can be explained by the increase in the hydrogen ion concentration in the fluid column as compared with that of the zone of set cement. This shift is interpreted to represent the top of cement in the well. To dispel the concern that any lithological change caused this anomaly, an analysis was performed with the SP curve, gamma ray, microlog, and formation density log. This analysis did not show any significant lithological break at this depth. JPT P. 1089

Gas Injection With Radioactive Tracer To Determine Reservoir Continuity-East Coalinga Field, California

Radioactive tracers injected with natural gas revealed that desaturated intervals were often continuous over wide areas of the field; those intervals could greatly influence an injection project by acting as thief zones for injected water. The tracer study suggested generally better reservoir sand continuity than could be inferred from a related outcrop study. Introduction A waterflood pilot project, to start in 1974, has been planned for the Temblor Zone II reservoir of the East planned for the Temblor Zone II reservoir of the East Coalinga field, Calif. This proposed five-spot pattern drive project has required data on reservoir continuity and fluid distribution that have not been readily available from a study of a nearby outcrop nor from modem indirect geological methods., Engineering and geological studies indicated that this gravity drainage reservoir consists of complex channel sand deposits having uncertain interwell continuity complicated by oil desaturated intervals (intervals having a gas saturation and a low gravity-drainage residual oil saturation). Many of these sands contain sufficient movable oil associated with gas intervals to be included in a supplemental oil recovery project. A geological outcrop study was carried out approximately 2 miles northwest of the project study area to develop a conceptual picture of the Temblor Zone II reservoir. To learn more about this reservoir and to follow up the outcrop study, a series of reservoir characterization tests was undertaken. The tests consisted of injecting gas with radioactive tracers into the desaturated intervals. After a study of the out-crop, it was concluded that the subsurface geological features associated with channel boundaries would limit reservoir continuity to the channel width of 300 to 500 ft in all major sands, with better continuity along the trend of the channels. This restricted continuity would severely limit an injection project, but the results of the gas tracer tests indicate that the effective reservoir continuity is much greater than the continuity inferred from the outcrop. Method of Testing Gas tracer surveys were carried out successfully in Temblor Zone II sands, which had desaturated intervals with considerable continuity, Fig. 1 is an oil saturation profile based upon core analysis data for the gas injection well. The oil saturations within the sands having no desaturation have been reduced by the flushing action of the mud filtrate during coring. Some desaturated intervals are shown to overlie movable oil intervals and some desaturated intervals cover entire sand members. The sand in this reservoir is unconsolidated, so in obtaining all rock data, modem procedures for handling unconsolidated core were procedures for handling unconsolidated core were used and rock properties were measured under confining pressure. The well was completed with casing set through the Temblor Zone II formation so that individual sands could be isolated by tubing and packers in the overbore for each of the injection test. packers in the overbore for each of the injection test. The well completion consisted of perforating the desaturated intervals in four sands. To insure that the injected gas had been injected into the right sand, normal radioactive gas injection profile surveys were run at the conclusion of each phase of the testing before the packers were moved. The injection tests were conducted in separate phases using methane containing a radioactive tracer phases using methane containing a radioactive tracer at the constant rate of 500 Mcf/D. JPT P. 1251

Radiotracers in Gas-Liquid Transportation Problems-A Field Case

Presented here are the results of a field program to develop and Presented here are the results of a field program to develop and evaluate radiotracer techniques for simultaneously measuring linear velocities of the individual phases of a multiphase stream. The flow properties monitored were used to compare experimental two-phase pressure drops with values predicted by techniques currently used pressure drops with values predicted by techniques currently used in design work. Introduction Numerous studies have been published on the transportation of gas-liquid mixtures through pipelines. However, the range of applicability pipelines. However, the range of applicability of most of the methods suggested for describing two-phase flow is generally limited to the conditions under which the investigations were performed. This shortcoming can be attributed performed. This shortcoming can be attributed either to improper design and instrumentation of the experiments or to departure of the analytic models, upon which the correlations are based, from the physical model or both. Therefore, further research in two-phase flow is needed to obtain more meaningful data for the solution of gas-liquid transportation problems. A prerequisite to understanding two-phase flow in a pipe is an adequate knowledge of the interrelationship between the velocities of the individual phases, individual densities, the gas volume fraction and the gas weight fraction. It is very difficult, however, to measure the relative velocities of the individual phases. In addition, the method most commonly used in the past to obtain the vapor volume fraction was very unsatisfactory. It constituted isolating a portion of the pipe by means of quick-closing valves, and subsequently measuring the actual quantity of liquid present. The volume fraction of vapor obtained in this manner was an average value over the length of the test section, so the effect of geometrical changes on density of the two-phase mixture could not be accurately determined. These are serious shortcomings of previous investigations of two-phase flow. In recent years a technique that has become more common for measuring fluid flow involves the use of radioactivity. This technique now offers easy and accurate means of measuring the linear velocity of each individual phase (radioactive tracer survey), and both the density and void fraction (gamma-ray attenuation). The method reported here to determine linear phase velocities is the Isotope Velocity method; a slug of radioactive material is injected rapidly into the flowing stream, and the transit time of the radionuclide between positions of known detector separation is measured. The accuracy of such a flow measurement depends upon the strength of the gamma rays emitted by the chosen isotope, accurate knowledge of the internal dimensions of the pipe, detector sensitivity and velocity profile. JPT P. 939