Advances in Openhole Well Logging
- R.D. Felder (Exxon Exploration Co.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- August 1994
- Document Type
- Journal Paper
- 693 - 701
- 1994. Society of Petroleum Engineers
- 1.6 Drilling Operations, 2.4.3 Sand/Solids Control, 7.6.6 Artificial Intelligence, 1.12.1 Measurement While Drilling, 1.2.3 Rock properties, 4.3.4 Scale, 1.5 Drill Bits, 1.6.9 Coring, Fishing, 1.12.2 Logging While Drilling, 5.1.5 Geologic Modeling, 5.1 Reservoir Characterisation, 3.3.2 Borehole Imaging and Wellbore Seismic, 5.5.2 Core Analysis, 5.2 Reservoir Fluid Dynamics, 2.2.2 Perforating, 1.6.7 Geosteering / Reservoir Navigation, 5.6.1 Open hole/cased hole log analysis, 1.12.3 Mud logging / Surface Measurements, 7.6.2 Data Integration, 4.1.5 Processing Equipment
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Distinguished Author Series
Openhole well logging comprises a broad spectrum of measurements thatincludes mud, measurement-while-drilling (MWD), and conventional wireline logs.These measurements are the primary source of formation evaluation data used inapplications ranging from individual drilling-well appraisals to comprehensivereservoir description studies. Openhole well-logging technology continues toevolve to address the needs for improved accuracy in measuring reservoirproperties. Numerous technology advances have recently occurred. This paperpresents several examples of new developments and applications to illustratethe current state of technology and to offer insight into future developmenttrends.
Significant developments have recently been made in openhole well-loggingtechnology, despite a major downsizing in the industry. New measurement toolsand software systems have been introduced in an effort to provide accurate,cost-effective methods for addressing a variety of formation evaluationchallenges, which include thin-bed evaluation, low-resistivity pay analysis,productivity/permeability prediction, horizontal well evaluation, fracturedreservoir analysis, and reservoir geology characterization.
Advances have been made in a variety of logging technologies. Enhancementsin log data acquisition include higher data sampling and transmission rates andexpanded computer capabilities to process log data and to control loggingoperations. The latest borehole imaging tools offer improved image quality fromboth microresistivity and acoustic imaging logs, which has led to growingapplications. New multielectrode induction and laterologs provide enhancedthin-bed resolution and new formation measurements. Source, detector, andprocessing enhancements offer improved porosity and elemental analysis accuracyfrom nuclear logging tools. New acoustic logs provide multipole source andreceiver arrays to measure compressional, shear, and Stoneley wave data in bothhard and soft formations.
In addition, new nuclear magnetic resonance logs offer greatly improved dataquality for determining porosity, irreducible water saturation, and otherformation and fluid properties. Wireline formation tester developments providenew downhole measurements, pump-out capabilities, and a modular design thatallows multiple configurations. Advances in MWD logging include new resistivitymeasurements, improved porosity/lithology logs, and new applications. Finally,developments in log data processing and interpretation provide fasterprocessing, more information from the log measurements, and more effectiveintegration of data from multiple sources, such as drilling, mud logging, coreanalysis, geology, testing, and production.
The growing trend of increased numbers of downhole sensors and greatermeasurement sampling frequency for improved resolution has put new demands onwell-log data acquisition systems. These systems comprise the hardware andsoftware for sending data uphole from the logging tool; for receiving,processing, verifying, presenting, and storing data at the surface; and forelectronically transmitting data from wellsite to office locations.Developments in downhole signal processing and data compression techniques aredramatically increasing the uphole data transmission rates to meet therequirements of new measurement tools. New wireline systems provide ratesexceeding 500 kbit/sec, and future systems offering several megabits per secondare expected in the near term. MWD transmission rates, based on mud-pulsetelemetry, have also shown improvement, but they remain a limiting factor forreal-time data acquisition in some cases. MWD data transmission rates haverecently increased from 3 to 12 bits/sec, and further improvements areforeseen.
The capabilities of computer surface equipment to process log data and tocontrol logging operations have also increased significantly. This has resultedin more efficient logging operations, improved quality control of log data,enhanced wellsite log analysis products, and improved methods for storing andtransmitting data. These improvements have been made possible by usinghigh-speed, multitasking workstations in wellsite logging units.
Significant improvements have recently been made in the quality of boreholeimaging measurements, which have led to growing applications of thistechnology. These measurements are commonly used for thin-bed evaluation,fracture identification and analysis, structural and stratigraphic dipanalysis, sedimentary facies analysis, and textural analysis. Technologydevelopments have led to (1) better assessment of reserves in thinly beddedreservoirs; (2) improved definition of fracture density, aperture, andorientation for producibility estimation and perforation placement; and (3)greater geological information, such as definition of structural dip,paleocurrent direction, rock facies, flow barriers, and porosity types. Ref. 4gives a good overview of borehole imaging technology and its applications andcontains a collection of technical papers describing the development ofborehole imaging from its beginning until 1989. The primary techniques foracquiring borehole image data use electrical (microresistivity) or acousticmeasurements.
Microresistivity Imaging. Microresistivity imaging tools produce an image ofthe borehole wall by mapping its resistivity with an array of small,pad-mounted, button electrodes.
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