Abstract. MICROTOPS II is a five-channel, handheld Sun photometer that can be configured to measure total ozone, total water vapor, or aerosol optical thickness at various wavelengths. The instrument measures 10 x 20 x 4.3 cm and weighs 600 g. A principal design goal was the measurement of total ozone to within 1% of ozone measurements made by much larger, heavier, and more expensive Dobson and Brewer spectrophotometers. This goal has been met for a maximum air mass of up to -2.5, as demonstrated by comparisons of MICROTOPS II and its immediate predecessor, Supertops, with Dobson and Brewer instruments at various locations. Conventional interference filters are subject to gradual and unpredictable degradation. MICROTOPS II avoids these problems by using highly stable ultraviolet filters manufactured with an ion deposition process. The 2.4 nm (FWHM) band pass of the UV filters was selected to balance noise and ozone measurement performance. The optical collimators and electronics of the instrument were carefully designed to optimize pointing accuracy, stray light rejection, thermal and long-term stability, signal-to-noise ratio, and data analysis. An internal microcomputer automatically calculates the total ozone column based on measurements at three UV wavelengths, the site's geographic coordinates, and universal time, altitude, and pressure. The coordinates can be entered manually or by a Global Positioning System (GPS) receiver. A built-in pressure transducer automatically measures pressure. MICROTOPS II saves in nonvolatile memory up to 800 scans of the raw and calculated data. Measurements can be read from a liquid crystal display or transferred to an external computer. IntroductionAerosols and ozone within the atmosphere modulate the intensity of ultraviolet radiation at the surface of the Earth. Since ozone absorbs shorter wavelengths more effectively than longer wavelengths, the ratio of the intensity of direct sunlight at two wavelengths within the range of 300-320 nm is related to the total abundance of ozone in a column through the atmosphere. This forms the basic operating principle for a variety of instruments that measure the ozone layer. The bestknown ground-based ozone-monitoring instruments are the Dobson and Brewer spectrophotometers. Both these instruments divide sunlight into its constituent wavelengths by means of a spectrometer. The dispersing element is a quartz prism in the Dobson and a diffraction grating in the Brewer.While the Dobson and the Brewer are universally accepted instruments for measuring column ozone, these instruments are expensive, heavy, and large. There has long been a need for 14,573
The first Magnetic Resonance While-Drilling (MRWD) tools have been built and field tested. The hardware was designed to provide data compatible with the Magnetic Resonance Imaging Log (MRIL®) wireline tool in terms of processing and interpretation. The paper discusses the theory of robust MRIL measurements in the drilling environment and reviews the theory of T1 measurements. We report on the results of a field test in the Gulf of Mexico. The MRWD device logged the entire TD run from casing to TD and provided additional hydrocarbon-typing data in wiping mode over the target zones. Wireline MRIL data and conventional logs were used to verify the MRWD measurements. Introduction We previously reported on our initial field experiences with the Magnetic Resonance While-Drilling (MRWD) tool in a recent transaction paper.1 The present paper focuses on the petrophysical deliverables of the MRWD measurement and their robustness in the drilling environment. Furthermore, we report on a field test conducted in the Gulf of Mexico in March 2000. The test was run with an experimental prototype version (EX) and we were able to compare the results with wireline data from the MRIL-Prime tool.2 The comparison indicates satisfactory performance both during drilling and wiping operations. The primary application areas of MRWD will be high-cost offshore exploration and development wells, potentially in deep water. Typical bit sizes for the final TD run are 8–1/2 to 10–5/8 in. High rates of penetration (ROP) and long bit runs are common, aided by poorly cemented sediments, oil-based mud systems and advanced bit technologies. In this context, open-hole logging operations are expensive in terms of added rig time and risky in terms of hole stability. Additional problems are highly laminated reservoirs (e.g. turbidites) that frustrate traditional log interpretation because electrical and nuclear measurements may show little or no contrast identifying reservoir rocks. In these situations, breakthroughs in reservoir characterization have been achieved by computing hydrocarbon volumes directly from MRIL data, circumventing the problems with conductivity/resistivity.3 Real-time MRIL data from an LWD device will result in faster, better and cheaper evaluation and exploitation of these reserves. Logging-while-drilling (LWD) tools are expected to replicate as close as possible the functions of their wireline counterparts. In particular, the expectations for the LWD version of an MRIL device are:To provide a measure of rock porosity that is lithology-independent and that does not require radioactive sources;To collect a spectrum of NMR relaxation times that is suitable for input to lithology models that estimate bound fluid volumes, free fluid volumes and rock permeability;To enable fluid typing by exploiting the inherent differences in T1 and/or T2 (longitudinal and transversal relaxation times) between the water, oil and gas phases;To withstand the shock, vibration and erosion associated with drilling;Not to interfere with the drilling process; andNot to interfere with any other LWD or MWD measurements. Tool Hardware and Sensor Physics Fig. 1 shows the basic tool layout conforming to these requirements. The tool has two main sections: the sensor and the electronics package. The total length of the EX version tool of 42 ft is driven by the inclusion of extra electronics and will be reduced in the forthcoming commercial tool. The tool diameter is under-gauge at about 7–1/4 in. All compressional, torsional and tensional stress ratings exceed those of standard 4½ IF API connections. To meet the sensor-to-sensor non-interference requirement, a distance of 45 ft to the MWD directional package is recommended.
A recently introduced azimuthal resistivity LWD imaging tool has been upgraded with advanced high resolution sensors that are capable of differentiating reservoir and borehole features down to a size of 0.4 in. when drilling in well consolidated formations. The high vertical and azimuthal resolution, along with 100% borehole coverage, yield an image quality comparable to that of wireline service for applications that include fracture characterization and formation evaluation. This paper describes a field test of the high resolution tool in 5 7/8" and 8 3/8" holes in Saudi Arabia and shows the application of LWD images for estimating carbonate reservoir producibility involving the characterization of secondary porosity. The LWD imager provides significant economic and logistic benefits, especially in slim horizontal sections; in addition, it can identify fractured zones with mud loss potential shortly after penetration. The real-time resistivity provides a good basis for accurate dip calculation and geosteering in general. In its default configuration, the high resolution tool is equipped with six high resolution sensors arranged in two rows. One of the benefits of the multi-sensor configuration, demonstrated by the field test, is the ability to validate the image quality by comparing data from various sensors. Another benefit is the depth correction achieved by correlating images from identical sensors located at various depths. The paper also discusses the fundamental principles behind high resolution resistivity imaging in conductive mud and makes extensive use of modeling techniques to characterize the sensor performance in various practical situations.
Summary The first Magnetic-Resonance-Image Logging-While-Drilling (MRI-LWD*) tools have been built and field tested. The hardware was designed to provide data that are compatible with the Magnetic Resonance Imaging Log (MRIL®) wireline tool in terms of processing and interpretation. This paper discusses the theory of robust MRIL measurements in the drilling environment and reviews the theory of 7 relaxation time measurements. We report on the results of a field test in the Gulf of Mexico. The MRI-LWD device logged the entire total depth (TD) run from casing to TD and provided additional hydrocarbon-typing data in wiping mode over the target zones. Wireline MRIL data and conventional logs were used to verify the MRI-LWD measurements.
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