Inversion-based petrophysical interpretation of multi-detector logging-while-drilling sigma measurements

textPulsed-neutron borehole measurements involve a physical process in which a source emits energetic neutrons that lose energy upon collisions with formation nuclei, and are eventually captured by a nucleus to form a heavier, excited state. The excited nucleus decays to its ground state by the emission of gamma rays. Both thermal-neutron and gamma-ray populations decay with time at a rate defined by Sigma, which is a nuclear property that quantifies a material’s ability to capture thermal neutrons. The large contrast in Sigma between hydrocarbon and salty connate water enables calculations of water saturation directly from pulsed-neutron measurements. Sigma logs have proven useful in the assessment of thinly bedded formations because they exhibit a small volume of investigation, and have been deemed superior to resistivity logs in the petrophysical evaluation of carbonate formations. The recognized potential of Sigma logs in formation evaluation initiated the development of multi-detector Logging-While-Drilling (LWD) Sigma measurements. These measurements are acquired using one thermal-neutron and two gamma-ray detectors at different spacings from the source. Such a design is aimed at providing distinct radial depths of investigation to detect filtrate invasion in the near-wellbore zone. Despite their formation-evaluation potential, multi-detector time-decay measurements commonly remain affected by invasion, shoulder-bed, and well-deviation effects. The purpose of this dissertation is to develop a fast-forward simulation method to reproduce multi-detector time decays and combine the method with inversion techniques to improve the petrophysical interpretation of LWD Sigma measurements. First-order perturbation theory and a library of pre-calculated Monte Carlo detector-specific sensitivity functions and time decays are used to numerically simulate borehole Sigma measurements in realistic logging environments. The new simulation method is one hundred thousand times faster than rigorous Monte Carlo calculations and remains within two capture units of disparity. Next, the fast-forward simulation method is embedded within inversion algorithms to estimate layer-by-layer radial length of invasion and formation Sigma corrected for shallow invasion, shoulder-bed, and well-deviation effects. Both fast-forward and inverse modeling algorithms are benchmarked against laboratory and synthetic time decays. The improvement of formation Sigma obtained with inversion-based interpretation leads to an improvement in the estimation of Sigma-derived water saturation. Likewise, the estimated radial length of invasion is combined with neutron and density measurements to correct the latter for invasion effects. Results indicate that the inversion-based interpretation method is well suited for the evaluation of high-porosity formations invaded by salty mud filtrate. Inversion-based interpretation of field LWD time decays enables the estimation of lower values of water saturation when compared to conventional Sigma interpretation or resistivity methods. Estimated values of water saturation are as much as fifty percent lower than predicted by conventional interpretation of Sigma logs in the case of measurements affected by shoulder-bed effects, and as much as one hundred percent lower than predicted by the conventional interpretation method for measurements additionally affected by salty filtrate invasion. The key attributes of the combined petrophysical interpretation of multi-detector Sigma, neutron, and density measurements developed in this dissertation are that it explicitly enforces the physics of all nuclear measurements, honors the pressure and temperature dependency of reservoir fluid nuclear properties, and takes into account a-priori information such as mud-filtrate salinity, connate-water salinity, and bed-boundary locations.Petroleum and Geosystems Engineerin

Recent developments in hole cleaning technology in deviated well bores for geothermal and petroleum

This paper is looking on recent developments in hole cleaning technologies and how recent advancements can be used to aid efficient hole cleaning in deviated wells. Successful hole cleaning relies upon integrating optimum drilling fluid properties with the best drilling practices. The ability of the drilling fluid to transport the drilling cuttings to the are determined by several parameters (cutting density, mud weight, hole-size, hole-angle, rheology of fluid, cutting size, rate of penetration, drill pipe eccentricity, drill pipe rotation speed, phase of fluid, cutting transport ratio and cutting bed properties). Efficient hole cleaning of deviated wells is important and difficult to perform efficiently, deviated wells normally uses drilling fluid with lower viscosity and gel building properties than in vertical section. Deviated wells are an important tool to either boost the return from existing fields or gaining access to new and formerly inaccessible formations. The increasing need for oil and gas have kept increasing with ever increasing energy output in the world, despite the world trying to swap to more renewable resources. Petroleum products such as coal, gas and oil still stand for over 80% of the energy production in the world. Increasing energy demands from the world exceeds the development within renewable technologies and gaining access to new formation and extracting most of the oil and gas in current formation will be paramount in giving people access to energy required to keep the world running. Percentage of world’s energy coming from renewable resources has increased and will hopefully keep increasing, but total energy demand especially from developing countries with increasing population and higher standard of living requires higher amount of energy than the countries are currently consuming with renewable being too expensive, inefficient, or lacking the required infrastructure for implementation. The paper is a compilation of recent developments and would hopefully give the reader insight in the processes most important efficient hole cleaning for deviated wells. The topic of efficient hole cleaning is complex, and a lot of different parameters will be introduced to understand the role of new developments. Basic understanding of these parameters and their interplay with each other is required to understand to keep the innovation with respect to efficient hole cleaning and automating more of the process involved in hole cleaning while drilling in deviated wells. The paper also uses the information from collected studies to write to a data code based on recent developments to aid in controlling the right rate of penetration (ROP) during drilling. No independent research was those in this paper and is based on the work of research and literature of others

Survey and comparison of petroleum well electrologging tools

The principles used in the design of electrologging tools used in the petroleum industry are reviewed. Examples of tools and methods are taken from Gearhart Industries, Schlumberger Ltd and Western Atlas Ltd who are the three major electrologging companies accounting for 93% of the world market share. The survey and comparison of the tools in each of the category used both during the exploration and development stage of a well and reservoir are made. The results are presented and discussed. Furthermore an insight to the future of this industry is presented

Simple methods for assessing groundwater resources in low permeability areas of Africa

In many areas throughout Africa, a staggering proportion of wells and boreholes fail. Failure can occur for a number of reasons – inadequate maintenance and community involvement, poor engineering or a lack of water. Often it can be difficult to work out the exact reason after the event. However, in many geological environments the impacts of poorly sited and designed boreholes and wells are a major concern to funding agencies, implementing institutions and local communities. In such areas, good supplies of groundwater cannot be found everywhere, and boreholes and wells must be sited and designed carefully to make use of the available groundwater. To appropriately site and design water sources, the groundwater resources of an area need first to be investigated to understand how water occurs in the ground. In this manual we present some techniques that allow a quick assessment of groundwater resources without requiring much expertise or expense. Some of the techniques are old and established while others are new. However, all techniques have been tested by BGS (and others) in assessing groundwater resources in Africa. This manual does not claim to be a detailed textbook for hydrogeologists – there are enough already (see reading list at the end of the chapter). Rather it is meant as a practicalaid for those involved in the practice of rural water supply, particularly in Africa. Little training or equipment is required for the tests and they can all be carried out in a short space of time. The manual is divided into six sections. The first gives an overview of the groundwater resources of sub-Saharan Africa (SSA) and discusses the scope and detail of investigations required in different geological environments. The remaining chapters describe simple techniques for assessing groundwater resources, from basic reconnaissance to assessing the yield of a borehole. In the appendix are summary sheets of the most common techniques which can be photocopied and used in the field

Petrophysical Variation in Central North Sea Fields

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X-Ray Fluorescence Analysis Of The Bakken And Three Forks Formations Of The Williston Basin, North Dakota And Well Logging Applications

This research analyzed nine core sections representing The Lower Bakken and Three Forks Formation of the Williston Basin in North Dakota using x-ray fluorescence. The Charlotte 1-22H core sequence from Continental Resources was also included to assess the elemental composition of the stratigraphic interval spanning the Lodgepole, Bakken, Pronghorn, and Three Forks Formations. Core samples were obtained from the North Dakota Industrial Commission (NDIC) Wilson B. Laird Core and Sample Library at the University of North Dakota. Core sections were exposed to x-ray at 15 keV and 45 keV excitation voltages to provide elemental spectra; count rate values were obtained and elemental ratios were then calculated to assess the geochemical composition and diagenetic changes within each stratigraphic interval. Results of x-ray fluorescence analysis of Williston Basin core included detailed well-logs showing the vertical distribution of lightweight, mid-range, and trace metal elements. The evidence collected in this research showed that x-ray fluorescence ratios can uniquely chronicle autonomous lithostratigraphic units with higher efficiency than conventional wireline or logging-while drilling technology. The x-ray fluorescence elemental ratios of Fe:Mn can more precisely determine formation contacts on core sections than conventional gamma ray or spontaneous potential methods. Furthermore, x-ray fluorescence will allow for unique identification of members and thin beds within larger formations. Elemental Ka fluorescence ratios of Fe:Mn, Fe:Ca, Fe:Rb, Fe:S, and S:Cl can precisely identify the Bakken Formation. Ratios of Ca:Mg, Ca:Rb, Ca:Zn, and Ca:Ti can precisely identify the Lodgepole, Three Forks, and Middle Bakken Formation. Furthermore, the ratio of Fe:Mn can be applied to the Middle Member of the Bakken Formation to identify unique lithofacies. This research only analyzed Williston Basin core, the results provided imply that calcium Ka fluorescence ratios can be used to identify any carbonate lithology; iron Ka fluorescence ratios can be used to identify any shale lithology

Estimating reservoir permeability with borehole radar

We would like to express our gratitude to C. Warren at Northumbria University for the valuable help in gprMax modeling and W. Filinger at The University of Edinburgh and J. Liu at the Delft University of Technology for their assistance in the high-performance computing. We acknowledge the Sinopec Petroleum E&P Institute for the permission to use the oil field logging and coring data. The research was funded by the National Natural Science Foundation of China (41674138, 41811530749, 41974165), the NWO Cooperation and Exchange Fund (040.22.011/7048), and the China Scholarship Council grant (201806415048). The work has been performed under the Project HPC-EUROPA3 (INFRAIA-2016-1-730897), with the support of the EC Research Innovation Action under the H2020 program, and used the Cirrus UK National Tier-2 HPC Service at EPCC (http://www.cirrus.ac.uk) funded by the University of Edinburgh and EPSRC (EP/P020267/1). DATA AND MATERIALS AVAILABILITY Data associated with this research are available and can be obtained by contacting the corresponding author.Peer reviewedPostprin

In situ determination of relative permeability and capillary pressure curves using multiphase flow rates and pressures of wireline formation testers.

Relative permeability and capillary pressure curves are crucial inputs for reservoir modeling and simulation. Measuring these quantities on core samples in a laboratory is a necessary, but lengthy process. Wireline Formation Tester (WFT) logging is routinely applied in field operations for reservoir evaluation purposes. Since a historical record of WFT data often exists for a field, we propose in our study to estimate multiphase flow properties in situ from the acquired WFT data in a relatively short period of time. The WFT tool records, among other measurements, bottomhole pressures, water-cuts and flow rates by pumping out fluids from a hydrocarbon bearing formation during the cleanup process in order to reduce the contamination level near the wellbore. The contamination, which is water based mud (WBM) filtrate in this study, invades from the openhole during drilling and changes the saturation of hydrocarbon and water in an invaded zone near the wellbore. The proposed methodology estimates multiphase flow properties occurring near the wellbore, such as relative permeability, capillary pressure, damage skin and mud-filtrate invasion by inversion of water-cut and bottomhole pressure recorded during the WFT cleanup. Although the mud-filtrate invasion and the WFT cleanup replicate, respectively, secondary processes of imbibition and drainage in the reservoir, our study is designed under the assumption that a single set of multiphase flow curves represents both imbibition and drainage processes. The study shows that the most important parameters are the curvatures of relative permeability and capillary pressure curves during the processes. Although they can be optimized, prior knowledge of saturation endpoints and depth of mud-filtrate invasion improves the results. Noise levels of WFT logging, and heterogeneities of reservoir properties should be integrated correctly in the study. The methodology uses a detailed numerical model of the invasion and cleanup processes, and WFT tool geometry coupled with an optimizer for the inversion. The model investigates reservoir and fluid properties, and represents the events accurately occurring during drilling, logging, invasion and cleanup. The results from synthetic and field examples demonstrate that relative permeability and capillary pressure, mud-filtrate invasion, damage skin can be estimated successfully in the inversion process

Establishing the Imperial Oilfield Case Study: Part 1 - Reservoir Appraisal and Characterisation

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