測井&儲層評價技術新進展——隨鉆測井篇

LOGGING WHILE DRILLING?

Wellbore position. Primer on Wellbore Positioning is an ebook published by the University of the Highlands & Islands (UK). It is freely available on their website.?

Ranging system. Halliburton introduced a new magnetic-ranging well-positioning method that does not require access to the target wellbore for the surface excitation. Instead, the surface excitation is connected to the wellhead of the target well, and it transmits a current signal along the cased-hole target well. The array gradiometer in the nearby drilling well receives the corresponding magnetic fields, and calculates the relative distance and direction between the two wells. This system, which was designed primarily for SAGD applications, eliminates the need for a wireline ranging tool deployment in the target well. It also has application in wellbore intersection and well positioning applications. Compared to existing systems, this one improves equipment logistics and eliminates the wireline ranging tool deployment, while reducing the cost and risk to the operator and the number of personnel needed to deliver the service.?

Continuous surveying. Researchers at the University of Calgary have proposed a low-cost strapdown inertial system (SINS), using three orthogonal MEMS accelerometers and three orthogonal MEMS gyroscopes to provide survey data along an entire well trajectory, without interrupting drilling. Conventional magnetometer- and gyroscope-based systems provide survey data at stationary surveying stations (30-m intervals). This type of system could eliminate the need for non-magnetic collars, and the small size of the MEMS sensors would allow its use in small-diameter wellbores. In a separate development, an advanced processing technique uses continuous D&I measurements to provide wellbore survey data at 3-m intervals.?

Survey accuracy. Several new models have been proposed for improving survey accuracy. The Colorado School of Mines, 3D advanced spline-curve model calculates the well trajectory, using continuous derivatives up to the third order, along the entire well path. The improved model allows more accurate wellbore positioning, more realistic estimates of borehole tortuosity, and a measurement of borehole rugosity.?

Initiating downhole directional surveys. Conventional directional survey devices use recycling of the mud pumps during pipe connections to trigger the directional survey and send the data to surface. Another method, described by Schlumberger, uses cessation of pipe rotation, rather than cessation of the mud pumps, to trigger a survey. Surveys taken using this approach can be made prior to the pipe connection. Following the connection, the drillstring does not have to remain stationary. This approach eliminates the need to recycle to pumps to take surveys, and enables surveying with a full, unchanged flowrate (constant BHP), which minimizes surge and swab effects, thereby reducing risks of borehole instability and stuck pipe. The surveying method reduces overall surveying time and has benefits in MPD, UBD, and air drilling.?

Dual-telemetry MWD. NOV Wellbore Technologies introduced a retrievable dual-telemetry MWD tool (BlackStar II) that combines the capabilities of electromagnetic (EM) and mud-pulse (MP) data transmission, Fig 1. With the BlackStar II retrievable MWD, switching from EM to MP transmission can be performed via EM or RPM downlinking to avoid costly trips to change out equipment. The modular design allows flexibility in configuring the toolstring to maximize operational capabilities. By incorporating a special translation module, a standard off-the-shelf mud pulser can be run with this system without modifications. The new system offers a full suite of MWD sensors, including directional, gamma, internal and annular pressure, axial and radial vibration, ROM and temperature.?

High-temperature systems. Halliburton introduced a high-temperature MWD/LWD service (Quasar Pulse/QuasarTrio) that offers full triple-combo logging capability in hostile environments up to 392℉, and pressures to 25,000 psi. The basic MWD service delivers directional, gamma ray, pressure-while-drilling and vibration data for precise wellbore placement in HTHP zones. The LWD service delivers resistivity, density, and neutron porosity. The resistivity tool has three T-R spacings, and provides 12 resistivity measurements over a range of investigation depths. The density tool uses a conventional Ce-137 source and dual detectors, and has improved stabilization electronics and software to provide a stable measurement over the full temperature operating range. The neutron-porosity tool is a conventional configuration, with an americium-beryllium nuclear source and a pair of He-3 detector banks. The service is available in 4?-in. and 6?-in. for boreholes up to 97/8-in.?

EM logging. Schlumberger introduced prototypes of its new electromagnetic look-ahead (EMLA) tool. It uses the same sensor technology, and operates with the same multispacing and multifrequency measurements, as the commercial ultradeep “look-around” directional resistivity tool used in the mapping-while-drilling service (GeoSphere). EMLA is modular and consists of a low-frequency transmitter inserted in the RSS, 1.8 m behind the bit. It has 2–3 triaxial receivers in the drillstring, offering a flexible configuration for different applications.?

This configuration can detect changes in resistivity, tens of meters ahead of the bit, at all incidence angles in vertical and low-angle wells. A compensated resistivity measurement is made 3 m from the bit, to provide a shallow resistivity measurement used in the interpretation inversion. Look-ahead capability can reduce drilling risk by allowing proactive geo-stopping, to establish casing points above a drilling hazard, or to optimize coring points in a target reservoir. Prototypes have been designed for 12?-in. to 14-in. boreholes. The tool’s primary application, to date, has been to drill the well section above the reservoir, closer to the top of the reservoir to avoid complications in the shale above the reservoir.?

Acoustic logging. Knowledge of shale anisotropy is critical for optimizing completion design. However, measuring shale acoustic anisotropy in horizontal wells, using wireline dipole tools, can be difficult, due to conveyance problems and inaccuracies in the required dispersion corrections. By contrast, a unipole tool configuration is more efficient at measuring azimuthal shear anisotropy in fast formations, because the transmitters and receivers are oriented in the same direction, and directly measure refracted head waves from the component compressional and shear measurements; no dispersion correction or inversion is required.?

Schlumberger’s oriented, unipole sonic measurement service (SonicPacer) has a symmetric array of two transmitters and four receivers, with a T-R spacing of 4 ft and an inter-receiver spacing of 1 ft; an array of tungsten slugs between each transmitter and receiver attenuates the tool collar-mode signal. The tool has a high-resolution, focused, pulse-echo transducer to generate ultrasonic standoff and amplitude measurements that can be used to make a high-resolution image of the borehole.?

Compressional and shear slowness results can be calculated downhole and sent uphole in real-time for rapid decisions. The raw sonic waveforms are stored in memory and can be processed, on surface, to produce an anisotropic stress profile to optimize fracturing operations. The tool is available in 4?-in. and 6?-in. collar sizes. Applications include: 1) completion optimization for unconventional reservoirs; and 2) assessment of horizontal well placement, using sonic images of geologic structures, borehole shape, and fracture identification and characterization.?

Large-hole tools. Halliburton introduced a 9?-in. version of its lithodensity tool (Azimuthal Litho density) for use in boreholes with up to a 17?-in. diameter. The larger tool provides the same functionality as its smaller counterparts, including azimuthal density and photoelectric and acoustic standoff measurements.?

Schlumberger introduced an 8?-in. version of its LWD NMR tool (proVision Plus) for use in boreholes between 10?-in. and 12 5/8-in. The larger tool has a 17-in. diameter of investigation and can accommodate mud flowrates up to 1,200 gal/min.?

Borehole imaging. In complex lateral and reservoir sections, the use of invert emulsion OBM is preferred over WBM, due to the higher performance provided by OBM and its ability to reduce operational risks. Although wireline resistivity imaging devices have been developed for specific use in OBM, LWD resistivity imaging tools are designed for use in conductive mud systems. Baker Hughes is testing an electrically conductive OBM system that supports the deployment of low-frequency, high-definition LWD resistivity imaging tools. The invert emulsion drilling fluid allows real-time, high-resolution resistivity imaging without sacrificing the performance of an OBM.?

Sampling-while-drilling. When sampling-while-drilling, it is essential that downhole estimates of fluid properties and fluid contamination are reliable, as these may be the only available estimates of clean-fluid properties in zones where fluid scanning was performed with no physical sample recovery. The contamination estimates, together with the real-time fluid property estimates, enable prediction of the uncontaminated fluid properties. Schlumberger compared downhole “field” estimates of fluid properties from sampling-while-drilling operations with laboratory PVT analyses made on the recovered samples and found good agreement, as did comparison of downhole-predicted clean-fluid properties with laboratory-cleaned estimates.?

In another development, Baker Hughes developed an advanced fluid-typing algorithm to simplify the interpretation of the cleanup process during sampling-while-drilling operations. The algorithm incorporates interpretation guidelines from field applications and includes information about the mud type from measurements of refractive index, compressibility, density, and sound speed. An independent analysis of the sensor data is performed for each fluid component, and the sensor readings are weighted, using the reliability and accuracy of the measurement system. Real-time display enables easier identification of the fluid type pumped and simplifies decision-making during the pump-out process.?