測井&儲層評價技術新進展——裸眼測井篇

Tractor Conveyance. Tractors provide an efficient alternative to LWD and drillpipe conveyance of logging tools in highly deviated and horizontal wells. Schlumberger’s all-terrain wireline tractor (UltraTRAC) is a 3 3/8-in. wheel-driven device, with active traction control and bidirectional capabilities. It can run on hepta- or monoconductor cable. Its modular design can be configured with 2 to 8 drives, with each unit providing up to 400 lbf of pulling force. Different size/design wheels are optimized for a range of well geometries and conditions. Extended-reach arms are capable of opening to 15 in., allowing the tool to adapt to variations in borehole geometry and washouts. A tandem sub enables independent surface control of the drives above and below the sub. This control helps operators navigate borehole restrictions and washouts.

?Acoustic logging: near-well imaging. Baker Hughes has extended the method of dipole shear-wave reflection imaging (DSWI) to imaging complex, near-well structural features and bed boundaries in slow formations surrounding salt-related features. Deep compressional-wave imaging is a new method of acoustic acquisition, processing and 3D visualization that uses low-frequency compressional body waves generated by a dipole source to increase the depth of investigation, thereby allowing imaging of fractures and structural features up to 100 ft away from the borehole with reduced attenuation effects. Integrating the new technology with resistivity logs, borehole imaging, and VSP, can improve the level of detail of structures surrounding the borehole.

?Borehole imaging. Exxon Mobil presented a new automatic dip-detection method to identify formation dip in horizontal and high-angle borehole images acquired by any dipmeter and pad-type image tool. It consists of three main steps: 1) determining an optimal sinusoidal trend on the image at each depth using a minimum-variance technique; 2) computing the contrast at each depth along the optimal sinusoidal line on the gradient image; and 3) locating bedding surface boundaries at depths with the highest contrasts. This method has substantially reduced interpretation time (up to 80%) and dip uncertainty in building earth models from image logs for logging tool-response modeling in petrophysical evaluation.

?Small-diameter fullbore micro-imaging tool. Schlumberger introduced a slim, full-coverage through-the-bit imaging tool, designed to acquire high-resolution images in lateral wells in unconventional reservoirs. The 2 1/8-in. tool comprises three measurement sections, each having four pads on bowspring centralizer arms that provide two independent calipers. Each pad has two rows of six electrical buttons, totaling 12 measurement buttons, for a total of 48 buttons per section, 144 total. Tool resolution is 0.2 in., and borehole coverage is 76% in 6-in. holes, and 57% in 8-in. holes. The tool provides six caliper measurements, and has a triaxial accelerometer to provide to acceleration and relative bearing, and is fully combinable with all other through-the-bit measurements.

?Nuclear logging. Weatherford introduced a new small-diameter, spectral gamma-ray tool as part of its line of compact logging devices. The 2?-in. tool can be deployed on wireline, or without wireline, in memory mode using a drillpipe shuttle.

?Gamma-ray calibration. An effort is underway to establish a worldwide network of gamma-ray calibration facilities by using tools that have been calibrated at different facilities. Preliminary investigations show it is possible to reconstruct the KUTh grades at facilities in Grand Junction, Colo. and in Adelaide, Australia, using calibration data taken at a completely different setup in the Stonehenge R&D site in The Netherlands.34

?Wireline formation testing. Shell’s formation-testing group authored several valuable best practices review papers. They cover the current state and future trends in downhole fluid analysis for reservoir evaluation, on methods for obtaining improved permeability estimates from WFT pressure transient data, and how to obtain representative water samples using WFT.

?Pressure tester. Baker Hughes introduced an advanced wireline formation pressure testing service (FTeX). The 3 7/8-in. single-probe tool can operate in borehole sizes ranging from 4?-in. to 16 in. and is rated to 350℉ and 30,000 psi, Fig 5. The service automates the operational sequence downhole to optimize tool controls and test parameters with minimal input from surface personnel, thereby reducing data inconsistencies and inaccuracies. The closed-loop system analyzes the pressure 100 times/sec, making micro-adjustments to the flowrate to optimize the pressure drop, while making sure to remove enough fluid. This allows the flowrate to go as low as 0.001 cm3/sec. Real-time control is used to eliminate supercharging. The formation response from the first drawdown is used to define a behavior for subsequent drawdowns in real time—this allows the service to determine optimal pressure measurements, leading to increased data accuracy and data acquisition in half the time required by similar tools.

?Slim-profile formation sampler. Weatherford’s compact formation sampler (MFTD) can acquire up to three 700-cm3 formation-fluid samples for PVT analysis, in borehole sizes ranging from under 3 in. to 14 in. The 2.4-in. diameter tool employs a self-centering design to reduce the risk of sticking, and it enables deployment on wireline or through drill pipe. Realtime and recorded pressure data acquired by the sampler can be used to calculate formation-pressure gradients, ascertain fluid-contact levels, determine fluid mobility, and define formation permeability.

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