Earticle

Tropical forests face degradation due to conventional logging practices. Reduced Impact Logging (RIL) offers a sustainable alternative, aligning with UN SDG 15: Life on Land. This study developed a scalable RIL classification system to evaluate logging sustainability in tropical rainforests using ten parameters, and a structured field sheet with clear instructions was created to guide concession evaluations. The parameters were scored on an ordinal scale of 0 to 2, summing to a maximum of 20. A minimum threshold of 14 distinguishes RIL from Conventional Harvesting (CH), categorizing operations into six levels: Conventional Harvesting (＜14), Beginning RIL (14), Level 1 RIL (15), Level 2 RIL (16), Level 3 RIL (17), or Complete RIL (18-20). Unlike binary compliance frameworks such as FAO standards, this system introduces graduated ordinal scoring, a six-level classification hierarchy, and a mobile application, advances absent across all prior frameworks including the carbon-focused RIL-C approach of Ellis et al. (2019) and the Grünberg et al. (2023) systematic review of logging sustainability criteria. A web application called RIL Scoring App was developed with React.js, ExpressJS, LocalStorage, and EmailJS, hosted at https://ril-scoring-app.netlify.app/. Field assessments in Cameroon’s Forest Management Units (FMUs 11-002, 11-005, 11-006), using nine operational parameters, yielded scores of 8-9/18, classifying all three as Conventional Harvesting. Statistical validity was confirmed through non-parametric tests showing no significant score differences across FMUs (Kruskal-Wallis: p=0.947; Friedman: p=0.717), and perfect Spearman correlation between FMU 11-002 and 11-006 (r=1.000) further validated scoring consistency. Critical gaps were identified in log suspension and logyard management, while logging map preparation and timber identification scored consistently high. Challenges including governance gaps and high training costs necessitate subsidised programs and policy reforms. By standardising RIL evaluation, this framework offers a scalable model to balance timber production with sustainable forest management.

With an increasing demand of timber production, the use of heavy machinery in forest management has significantly increased, causing the changes of soil physical properties and the decline of long-term site productivity. This study was conducted to evaluate the effects of logging slash and machine passes(Harvester 1 pass & Forwarder 10 passes) on physical properties in harvester and forwarder operations. The results indicated that soil bulk density in the non-slash treatment site increased 10%-29%(25~139% in soil penetration resistance) at all soil depths, compared with the slash treatment site. Therefore, the creation of a slash mat could be an effective way to minimize the changes of soil physical properties. In addition, 90% of total soil compaction in slash treatment site was created within harvester 1 pass and forwarder 5 passes. In non-slash treatment site, 84% of total soil compaction was created within first harvester and forwarder passes.

In recent years, the spread of pine wilt disease in South Korea has resulted in a steady increase in tree mortality within coniferous forests. To prevent further transmission of the disease, salvage logging operations are being carried out in affected areas. This study evaluated the productivity and costs of a salvage logging system employing a cut-to-length method, in which sawlogs and logging residues are separately collected and treated. The harvested sawlogs were fumigated, while the residues were chipped using a mobile chipper, enabling safe utilization of the timber products without the risk of disease transmission. The sawlog production process consisted of chainsaw felling and processing, woodgrab-based extraction, and minor transporttation operations. Residue collection did not incur additional felling costs due to the free-ride effect, as it was generated as a by-product during sawlog felling. The results showed the unit costs for sawlog felling, processing, and extraction were 2.42 USD/m³, 2.48 USD/m³, and 4.00 USD/m³, respectively. For logging residues, the unit costs for processing, extraction, minor transportation, and chipping were 3.84 USD/GT, 15.44 USD/GT, 7.33 USD/GT, and 8.67 USD/GT, respectively.

Although mechanical harvesting equipment used in forestry operations increases productivity, it also causes significant physical impacts on the soil. Among the most prominent of these effects are road deformations and wheel rut depths caused by tractors and similar vehicles. Such deformations can disrupt the physical structure of the soil, increase the risk of erosion, and damage forest ecosystems. In this study, wheel rut depths formed during ground-based skidding operations were comparatively analyzed using both manual measurement techniques and imagery obtained via Unmanned Aerial Vehicles (UAVs). The fieldwork was conducted during forestry production activities in the Dağtekke Forest Management Chief. Manual measurements were performed using a ruler and lath along skidding trails, and the same areas were captured using UAVs and converted into digital surface models. The results obtained from both methods were compared using correlation analysis and paired sample t-tests. The findings revealed a high level of consistency between UAV-based and manual measurements, indicating that UAV technology offers a fast, contactless, and reliable alternative for monitoring. This study provides valuable insights into precision soil monitoring and assessing the environmental impacts of mechanical equipment in forestry operations.

Post-fire salvage logging operations are essential for mitigating secondary disaster risks such as debris flows and landslides by removing unstable woody debris. However, current practices involve scattered harvest unit development requiring extensive spur road construction, raising concerns about soil disturbance and infrastructure damage vulnerability during precipitation events. This study investigated spur road construction characteristics and damage patterns following salvage logging operations in the 2019 wildfire-damaged areas of Gangneung-si, South Korea. Eleven harvest units covering 851.6 ha were classified into four geometric configurations (square, rectangular, triangular, irregular), and spur roads were categorized by location into contour, slope, and valley types. Field surveys identified 92 damage locations with an average length of 77.1 m per site. Results showed significant variations in road density by harvest unit shape, with rectangular units exhibiting the highest density (58.6 m/ha) and irregular units the lowest (20.3 m/ha). Damage ratios varied dramatically by road type: valley roads showed 50% damage, slope roads 45%, and contour roads only 1%. Notably, triangular harvest units demonstrated the lowest damage rates (23.7%) despite high proportions of slope and valley roads, attributed to gentler longitudinal gradients in foothill locations. The study concludes that increasing contour- oriented road proportions and implementing slope roads with gradients below 20% can significantly reduce infrastructure damage and maintenance costs in post-fire salvage operations.

사용자 중심 디자인과 콘텐츠 개발이 대두되면서 사용성 평가에 대한 연구와 항목 정립이 중요해지고 있다. 그렇지만, 모바일 애플리케이션이나 특정 분야에 대한 디지털 시스템에 대한 사용성 평가에 대한 연구는 미비한 상태이다. 최근 웨어러블 기기와 스마트 폰의 발달로 자기 정량화(Quantified-self) 또는 라이프 로깅에 대한 사용과 콘텐츠 개발이 급증하고 있다. 본 논문은 라이프로깅 서비스를 지원하는 애플리케이션에 대한 사용성 평가 항목과 요인을 정립하고자 하는데 있다. 본 연구를 위하여 첫째, 라이프로깅 애플리케이션의 사용성 평가 요인을 정립하기 위하여 기존의 사용성 평가 항목을 수집하고 FGI(Focus Group Interview)를 통해 초기 항목을 선정하였다. 둘째, 선정된 초기 항목에 대한 사용성 평가 설문을 진행하여 그 결과에 대해 신뢰도 분석과 탐색적 요인분석을 실시히였다. 셋째, 통계 분석 결과를 통해 28가지 사용성 평가 항목과 4가지 요인인 인식성, 기능성, 심미성, 만족성을 정립하였다. 마지막으로 정립된 사용성 평가에 대한 활용 기대와 한계점을 논의할 것이다. 본 논문의 결과는 계속 증가하고있는 라이프로깅 애플리케이션의 사용성 평가 시 가이드라인으로 활용되어 효과적인 콘텐츠 개발에 기여할 것이다.

As user-centered design and content development emerge, the research and the establishment of items on usability evaluation are becoming more important. However, research on usability evaluation for digital systems in specific areas of mobile applications is still incomplete. Due to the recent development of wearable devices and smartphones, development and usage of quantified-self and life-logging applications has been rapidly increasing. This study aims to establish evaluation items and the main factors for the usability assessment of the applications that support life-logging services. In order to establish evaluation factors for life-logging application usability, we first gathered existing usability assessment items and selected the initial items through the Focus Group Interview(FGI). Second, we conducted user assessment surveys on the selected initial questionnaires and performed reliability and exploratory factor analyses based on the survey results. Third, through the statistical analyses results, we established 28 usability assessment items and four factors: recognition; functionality; aesthetics; and satisfaction. Finally, we discussed the expectations and limitations of the established usability assessment. The results from this paper could be used as a guideline for the usability assessment of life-logging applications and thus will contribute to effective content development.

전자기유도검층은 노멀전기검층을 수행할 수 없는 환경에서 노멀전기검층의 대안으로 지층의 전기전도도를 측정하기 위해 개발되었지만 노멀전기검층을 사용할 수 있는 환경에서도 널리 이용되었다. 초기의 전자기유도검층 장비는 하나의 송신코일과 수신코일로만 구성되었지만 오늘날의 전자기유도검층 장비는 여러 개의 송수신코일로 구성되어 있으며 주로 유전개발을 위한 지층평가에 널리 이용되어 왔다. 전자기유도검층은 최근 국내에서 주로 지하수환경 조사나 지반조사에 적용 빈도가 높아지고 있다. 이 연구에서는 먼저 두 개의 코일 시스템으로 된 전통적인 전자기유도검층기를 가정하여, 한국에서 주로 볼 수 있는 지질구조 지층모형에 대해 검층반응을 수치모델링하고 분석한다. 특히, 시추공 공경 변화와 시추공 이수의 전기전도도가 전자기유도검층에 미치는 영향을 분석하고 전자기유도검층과 노멀전기검층 반응의 차이에 대해서도 비교, 분석한다. 수치실험 결과, 전자기유도검층은 노멀전기검층에 비해 시추공 공경 변화나 시추공 이수의 전기비저항의 영향에서 자유롭다는 것을 알 수 있다.

Induction logging devices have been used in groundwater investigations and geotechnical engineering problems in Korea, even though induction logging devices had been originally developed for the oil industry applications. Standard (or conventional) induction logging devices usually incorporate one transmitter coil and one or a number of receiver coils (all of which are oriented along the tool axis), being sensitive only to the horizontal formation resistivity in vertical wells. We simulate and analyze induction logging measurements in a typical formation model of Korea using a standard induction tool. Numerical tests analyze effects of the diameter or/and mud resistivity of borehole on induction logging measurements. Further, we compare responses of induction and (short and long) normal logging to the typical formation model under consideration. Numerical results confirm that induction logging experience less borehole effects than normal logging measurements.

지반침하 예측 및 지반안정성 평가를 위해서는 우선 안정성 문제의 핵심인 지하 공동의 규모, 형상 및 위치 등을 정확하게 파악하는 것이 중요하다. 본 연구에서는 석회암지역에서 물리검층을 수행하여 지반침하 조사에 있어서 물리검층의 적용성에 대하여 고찰하였다. 케이싱 내부에서 수행한 자연감마검층 및 감마-감마(밀도)검층 자료를 이용하여 석회암 구간, 빈 공동 구간, 점토로 채워진 석회암 공동의 분포를 추정하였다. 물리검층 자료에서 공동의 확인은 공경검층에서 측정의 최대값을 보이며 자연감마선과 밀도가 매우 작다. 하부 지반의 원위치 물성 파악을 목적으로 지반의 탄성파 속도와 밀도 분포를 파악하였으며, 이 물성치를 이용하여 동탄성계수를 산출하였다. 또한 조사지역의 천부 공동을 통한 지하수 유동을 확인하고자 지하수 유동 해석을 실시하였다. 조사 결과, 천부 심도에서 다수의 공동 및 점토충진 구간을 확인할 수 있었으며 이로부터 석회암 공동 밀집지역을 추정하였다. 각 시추공 별로 여러 심도에서 온도 및 전기전도도의 변화가 확인되며 이 구간은 석회암 공동 및 단층대를 통한 지하수의 유동으로 인한 변화로 판단된다.

Understanding the size, shape, and location of underground cavities should be given priority to effectively predict ground subsidence and evaluate ground stability. We conducted integrated geophysical well loggings in the limestone area and discussed their applications. The geophysical responses of natural gamma and gamma-gamma (density) logs provided information to map the distribution of limestone, limestone cavity, and cavity filled with clays. The cavity leaded to high caliper and low natural gamma radiation and density responses in contrast with limestone and clay. The vertical distribution of seismic velocity and density were described by full waveform sonic and gamma-gamma (density) logs to understand the in situ physical properties, and dynamic elastic modulus was estimated from these physical properties. Moreover, groundwater flow was investigated in order to assess the possible groundwater flow through the cavities. As a result of well logs, many limestone cavities and cavities filled with clays were detected at a shallow depth, and they were concentrated in some areas. The variations of fluid temperature and electrical conductivity enabled us to define the groundwater flow through the limestone cavities or faults.

클라이언트/서버 데이터베이스 시스템에서 로깅 기법을 사용하는 기존 회복 기법은 서버에서만 전체 로그를 관리한다. 이는 잠재적으로 각 클라이언트에서 수행되는 트랜잭션에 대한 로그 레코드의 전송 비용을 내포하고 있고, 네트워크 트래픽을 증가시킨다. 본 논문에서는 로그 레코드의 전송 비용을 제거하기 위해서 클라이언트 기반 로깅(client-based logging)을 지원하고, 중복된 before-image를 제거하고 재수행 전용 로그(redo-only log)만을 로깅하는 방법을 제안한다. 그리고 클라이언트 파손 시 클라이언트에서 자치적으로 한번의 후방향 클라이언트 로그 분석을 이용한 재수행 회복을 하고, 서버 파손 시 각 클라이언트에서는 병행적으로 후방향 클라이언트 로그 분석을 이용하여 회복해야 하는 페이지의 after-image만을 서버에 전송하며, 서버에서는 수신된 after-image와 후방향 서버 로그 분석을 이용하여 재수행 회복을 수행한다.

자기공명검층은 장비의 발달과 더불어 해석기술이 발달함에 따라 지층을 평가하는 가장 효율적인 검층으로 평가되기 시작하였다. 자기공명검층은 수소와 자기장의 상호작용에 따른 감쇠 시그널 즉, 종축이완과 횡축이완을 측정하며, 이때 측정된 자료는 저류층 내 유체에 존재하는 수소 원자에 대한 정보와 감쇠 속도에 대한 정보를 내포하고 있다. 측정된 자료는 보다 용이한 해석을 위해 T2 스펙트럼 그래프로 변환되는데 이를 T2 역산이라 하고, 역산방법과 자료의 보정의 정도에 따라 스펙트럼의 모양과 해상도가 달라지기 때문에 자기공명의 정확한 해석을 위해서는 먼저 정확한 자료처리가 필요하다. 역산을 통해 변환된 T2 스펙트럼그래프는 저류층의 공극률, 공극의 크기 분포, 유체의 종류 및 유착과 같은 중요한 정보를 포함하고 있으며, 이는 다른 검층자료보다 비교적 정확하기 때문에 이를 기초로 유체 투과도, 습윤성과 같은 정보를 예측 할 수 있다. 이 논문에서는 먼저 자기공명의 이론을 간략하게 설명한 다음, 자기공명검층으로부터 측정된 자료 처리 이론 및 역산 방법과 자기공명검층을 통해 측정된 자료의 해석 및 연구 동향 순서로 살펴보도록 하겠다.

Nuclear magnetic resonance (NMR) logging has become one of the effective logging methods to evaluate formation since the generations of NMR logging tools and interpretation techniques have improved. NMR measurements detect decay signal also called T2 relaxation corresponding between proton nuclei in the fluids inside the pore space and radio frequency pulse at the proton resonance frequency. The measured amplitude of the spin echo train, called decay curve, displays on a log as a function of depth and contains important information, such as density of hydrogen in the fluid and fluid type, yet exhibits multi-exponential decay due to variety of pore sizes. For ease of interpretation, the detected decay curve convert to T2 spectrum by using proper T2 inversion methods. The T2 spectrum not only could provide porosity, fluid type but also allow the identification and quantification of fluids in a reservoir. On the basis of these, the more petrophysical information such as permeability and wettability can be estimated. This paper briefly explains the basic theory of NMR first and describes NMR data interpretation including T2 inversion and T2 spectrum analysis.

최근 전 세계적으로 비전통가스인 세일가스, 치밀가스, 탄층메탄 개발의 중요성이 증가하고 있다. 지난 10여 년간 석유산업은 석유가격과 수요의 급속한 증가와 셰일가스 개발기술의 진전으로 비재래전통 가스개발로 이동하고 있다. 셰일가스의 개발은 기본적으로 가스 생산을 증대시키기 위한 수평시추와 수압파쇄에 의존한다. 그래서 총유기탄소량, 광물구성, 점토 특성, 메짐성과 응력의 분포 등에 대한 이해가 성공적인 수평시추와 수압파쇄의 기초가 된다. 수직 시추공에서의 물리검층, 수평 시추공에서의 LWD/MWD 자료는 세일가스 평가, 수압 파쇄 설계와 수압파쇄 이후의 효율검증에 중요한 역할을 한다. 결론적으로 다양한 물리검층 자료는 셰일가스개발의 의사결정 과정에서 중요한 핵심적인 정보라 할 수 있다. 이 논문에서는 북미 지역에서 개발하고 있는 셰일가스 개발 과정에서 적용되는 최근의 물리검층 기술을 소개하며 이들 정보는 셰일가스 개발을 이해하는데 많은 도움이 될 것이다.

Recently development of unconventional natural gases such shale gas, tight gas, coalbed methane is becoming important in the worldwide. Over the last decade, the shift of oilfield industry to unconventional plays has occurred as a results of the fast increase of oil and gas price and demand, and advances of development technologies in shale play. Exploitation of shale gas basically depends upon the horizontal drilling and hydraulic fracturing in order to increase the gas production. Therefore understanding for characteristics including total organic contents, rock mineralogy composition, clay type, brittleness and stress profile etc is fundamental to successful drilling and hydraulic fracturing. Geophysical well logging such as wireline logging in vertical exploration well and LWD/MWD (Logging While Drilling / Measurement While Drilling) in horizontal development well play a important role in evaluating gas shale, design of hydraulic fracturing, verifying the efficiency of post-fracturing. Shortly various geophysical well log data is a key information of decision-making processes in shale play. In this paper, the emerging technologies of geophysical well logging in shale play of North America introduced,and this article is useful to understand the role of geophysical well log in shale play.

Geophysical well logging is currently applied to the geotechnical investigation of the subsurface for the construction of tunnel and bridges, and the groundwater resources and environmental studies such as the characterization of fluid flow through fractured rock, seawater intrusion. The advantage of geophysical well logging lies in that the measurements of in situ physical properties of rocks and aquifer along the borehole in a continuous way. This article reviewed the published issues of geophysical well logging for geotechnical and groundwater environmental application in Korea. Firstly, the historical review of geophysical well logging in Korea introduced briefly, and the selected issues also summarized the research and practical oriented results based on the first trial. Finally, we suggest indispensable topics for the development of geophysical well logging.

최근 수년간 사물인터넷 기술은 급격히 발달하고 있으며 많은 분야에서 활용되고 있다. 사물인터넷 디바이스의 기능은 다양한 환경에서 정보를 수집하는 것이며 사용자에게 유용한 정보를 제공하여야 한다. 최근에는 사물인터넷 디바이스의 종류가 증가하고 있으며 가격도 저렴해지고 있다. 또한 사용하기 쉬운 오픈 소스 플랫폼들이 많이 개발되어 사용자에게 편의를 제공하고 있다. 본 논문에서는 ESP-12E NodeMCU 모듈 기반의 무선 데이터 전송 및 클라우드 서버 시스템을 설계하였으며 사물인터넷 디바이스에서 수집된 센서 정보는 WiFi 무선통신을 통하여 클라우드 서버에 전송하였다. 수집된 센서 데이터는 클라우드 서버에서 채널과 필드를 생성하여 저장되며 각 필드의 데이터를 그래프로 시각화하였다.

In recent years, the Internet of things has grown rapidly and is being used in many fields. The function of an Internet device isto collect information in various environments and to provide useful information to users. Due to recent developments in technology, the kinds of Internet devices are increasing and the prices are getting cheaper. In addition, many open source platforms that are easy to use have been developed and are providing convenience to users. In this paper, wireless data transmission and cloud server system based on ESP-12E NodeMCU module was designed and sensor information collected from Internet devices was transmitted to cloud server through WiFi wireless communication. The collected sensor data was saved by creating channel and field in the cloud server and the data of each field was visualized as a graph.

본 연구는 국내 가스하이드레이트 저류층에 대한 심층학습 모델링 연구의 기반을 제공하고자 한다. 이를 위해 유·가스 저류층 및 가스하이드레이트 저류층에서 물리검층 자료에 신경망 기법을 적용한 최신 기술동향을 분석한다. 물리검층 분야에서 신경망 기법을 적용한 국내외 연구사례들을신경망이 예측하고자 하는 출력자료 유형에 따라 저류층 암상 추정, 유체유동인자 추정, 지질역학인자 추정, 합성로그 생성 등 네 가지 적용 유형으로 분류하였다. 각 사례들의 주요 특징을 기술하는한편 특징들을 요약한 종합표를 제공한다.

This study aims to provide the fundamentals of deep learning-based modeling for gas hydrate-bearing sediments. For this purpose, we analyze state-of-the-art neural network applications in geophysical logs for conventional oil and gas reservoirs and unconventional gas-hydrate-bearing sediments. According to the type of neural network outputs, the previous studies are categorized into four application types: estimation of reservoir lithofacies, estimation of fluid flow parameters, estimation of geomechanical parameters, and generation of synthetic logs. For each type, we describe the key points of previous studies and provide summary tables.

최신 전자, 정보통신 기술을 활용하여 실시간 차분자기/편차 검층 시스템을 개발하였다. 전체 시스템은 존데, 500 m 전동윈치 모듈, 로터리 엔코더 모듈, 주 제어모듈과 스마트 디바이스로 구성된다. 존데는 길이 1.5 m 외경 48 mm 티타늄 하우징을 가지며 내부에 디지털 출력 초소형 고정밀 MEMS 기반 AHRS, 두 개의 3축 플럭스케이트 센서가 500 mm 이격되어 있는 아날로그 고정밀 차분 자기센서, 24 비트 analog-to-digital 고정밀 계측/제어 모듈이 포함된다. 개발된 시스템의 기초현장시험을 위해 울산 삼정리 반정 저수지 옆 440 m 시추공에서 0.3 m/s의 속도로 존데를 하강시키면서 2 Hz 연속측정을 수행하였다.

A smart device-based borehole deviation and magnetic gradient logging system is proposed. The whole system consists of a sonde, 500-m long electric winch module, rotary encoder module, the main control module, and a smart device. The sonde is made up of an attitude-and-heading-references-system based on digital output miniature high-precision microelectromechanical systems, a magnetic gradiometer sensor composed of two separated three-axis fluxgate sensors spaced 500 mm apart with analog voltage output, and a 24-bit analog-to-digital high-resolution acquisition/control module. The three component modules are situated in 1.5-m length 48-mm diameter titanium housing. To evaluate the performance of the system, preliminary field test was performed at 440-m borehole located in Ulsan samjeongri. The falling speed of sonde was 0.3 m/s and 2-Hz continuous measurement and monitoring were carried out.

느린 지층(slow formation)의 경우 음파검층을 통해 매질의 S파 속도를 측정하기 위해서는 다극자 송신원이 필요하다. 이 때 다극자 송신원은 적당한 부호들의 조합을 가진 단극들로 구성할 수 있다. 본 연구에서는 다극자 전파형 음파검층시 다극자 송신원을 구성하고 있는 단극들의 진폭 불균형이 검층 자료에 미치는 영향을 수치 모형 실험을 이용하여 조사하였다. 송신원의 진폭 불균형은 다극자 송신원을 구성하고 있는 단극들 중 하나의 진폭을 다른 것들에 비해 작게함으로써 구현하였다. 쌍극자와 사극자 성분들은 4개의 단극 수신기 배열들을 이용하여 이들 배열들의 반응을 서로 빼거나 더함으로써 얻었다. 진폭이 불균형한 쌍극자 송신원의 경우 굽힘 모드(flexural mode) 이외의 다른 모드들이 생성된다. 이 때 스톤리(Stoneley) 모드가 가장 강하게 나타나며 불균형의 정도가 심할수록 그 진폭이 커지게 된다. 쌍극자 송신원의 경우와 유사하게, 진폭 불균형 사극자의 경우 스톤리 모드와 같은 사극자 성분 이외의 성분들도 같이 생성되며 스톤리 모드의 진폭은 불균형의 정도가 심해질수록 진폭이 커진다. 하지만, 네개의 수신기 배열에서의 수신된 반응을 각각 A, B, C, D라고 했을 때, 검층기가 시추공 중심에 위치하는 한, 쌍극자의 경우는 A-C, 사극자의 경우는 A-B+C-D 자료처리를 통해 스톤리 모드를 제거할 수 있다. 그러나, 만약 검층기가 시추공 중심에서 벗어나 위치하거나 수신기 배열의 수신 정도가 같지 않을 경우에는 A-C 자료처리 과정 후에도 여전히 스톤리 모드가 남아있다.

To measure shear velocity of slow formation, we need multipole sources for acoustic logging. Multipole sources can be considered that they are constructed of monopoles with appropriate sign combination. In this study, the effects of mismatched multipole sources were investigated. To simulate mismatched dipole and quadrupole sources, we made the amplitude of one of monopoles smaller than those of the other monopoles. The dipole and quadrupole component were obtained with four monopole receiver array system by subtracting or adding appropriate responses. Mismatched dipole source excites nondipole modes in addition to the flexural mode. The strongest of these is the Stoneley mode, whose amplitude increases with increasing mismatch. Similarly, mismatched quadrupole sources produce nonquadrupole modes such as the Stoneley mode in addition to the screw mode. The amplitude of the Stoneley mode increases with mismatch. If we designate responses at receiver arrays as A, B, C, and D, we can obtain the flexural mode by A-C and the screw mode by A-B+C-D processing, respectively. But, in addition to a mismatched dipole source, when the receivers are mismatched or if the tool is off-centered, the Stoneley mode remains even after A-C processing.

가스 저류층 하부에 대수층 존재 시 가스 생산이 진행될수록 유체경계면이 상부로 이동하면서 지층수 생산은 불가피하다. 특히 다층 저류층 환경에서는 층간유동 및 물막힘(water blockage) 현상 등으로 인해 가스 생산성이 저하될 수도 있다. 심지어 가스 유량이 충분한 유속을 갖지 못할 경우 액체집적(liquid loading) 현상으로 인해 생산이 중단될 수도 있으므로 지층수에 대한 철저한 관리가 필수적이다. 이 연구에서는 다중센서로 측정된 다상유동 생산검층자료를 기반으로 다층 가스 저류층의 층별 생산성과 관내압력손실을 모사하는 다상유동 시뮬레이션 모델을 구축하고 현장 유량시험자료를 이용하여 검증하였다. 다양한 생산정 운영조건에서의 물 생산비에 대한 민감도 분석을 통해향후 가스 생산거동, 지층수 차단시점 및 차단효과를 예측하고 생산정 운영방안에 대한 가이드라인을 제시하였다.

In case an aquifer exists underneath a gas reservoir, water production is difficult to avoid as a fluid contact rises up by gas production. Especially in multi-layer gas reservoirs, gas productivity could be dramatically reduced by water production due to inter-reservoir crossflow or near-well water blockage. The well could be even killed if gas production rate is less than the minimum velocity to prevent liquid loading. Therefore, water production control is essential in terms of reservoir management. In this study, production logging data acquired by multi-sensor logging tool is used to estimate the productivity of each zone and to select the best matched flow correlation. Then, the results are utilized to construct a multiphase flow model and the model is validated with well test data. A sensitivity analysis for water cut is carried out under various operation conditions in order to estimate gas production performance and to predict the effect of water shutoff in the future and, as a result, the guideline for well operation is proposed.

Numerical experiments on the responses of full waveform acoustic logging in multi-layered anisotropic medium were performed with different anisotropic parameters and the results were analyzed. For the source of the logging tool, monopole and dipole source, which are mainly used in domestic logging survey, were considered. The responses of full waveform acoustic logging were calculated by discrete wavenumber method, and features of the responses were examined with changing the values of anisotropy parameters, ε, , and δ. In the case of the monopole source, the changes in anisotropy parameters have an effect on only the dispersion curve of Stoneley wave, not the velocities of P and S waves refracted at the borehole wall. The dispersion curve of Stoneley wave is most influenced by an anisotropy parameter, . For a dipole-source tool, the changes in the values of anisotropy parameters affect the dispersion curve of flexural wave similarly to the case of the monopole-source tool. However, for all cases, flexural wave propagates with the S wave velocity of the medium around the cut-off frequency.

Subsurface Drinage Problems arise from many causes. Flatland tends to be poorly drained, particularly where the subsoil permeability is low. There are many wet areas, however, where there is no evident connection between the area of seepage, or a high water table, and the topography of the site. High water tables may occur where the soil is either slowly or rapidly permeable, where the climate is either humid or arid, and where the land is either sloping or flat. This study is to bring light on subjects relating to increasing yield of crop and possibility of double crops a year in water logging paddy fields. Obtained results are briefly summarized as follows: 1. Effect of crop-yield in the plot A resulted 20.2 percent higher than the ordinary plot with yield of brown rice. 2. Possibility of double-crops a year is investigated. Effect of the barley production of the test plot resulted 168.2 percent higher than the other uplands near test plot with the yield of 1977 production and it is 3.8 percent higher compare with the yearly yields. 3. Decreasing depth of water level was measured 23.9mm per day and 14.3mm per day at the test plot and ordinary plot respectively and the amounts of subsurface drainage measured 30mm to 35mm per day. It is required that the relief well should be controled carefully and adequately. 4. Mean depth of ground water levl was measured 0.4∼0.5m regardless the width of corrugated pipe. It is significantly lowere than the ordinary plot(0.15∼0.20m) 5. The ground temperature of the test plot is higher 1 degree of centigarade or more than the ordinary plot and soil moisture content of the ordinary plot is higher 12.4∼27.8 percent than the plot reversely. There should be a relationship between rising of ground temperature and soil moisture.