The Azimuthal Density Neutron tool (ADN) is the latest generation density/neutron LWD tool provided by Anadrill; it supplants the CDN, which suffered from poor support and tool availability problems. It is deployed in similar fashion to the CDN and is combinable with other LWD tools. Unlike the CDN, the ADN can be configured to provide real-time apparent neutron porosity, formation bulk density and photoelectric factor data to characterize formation porosity and lithology while drilling. These nuclear measurements are borehole compensated for improved accuracy, standoff, and photoelectric factor measurements while drilling. 360-degree images of density and porosity result from the rotation of the tool's sensors through four quadrants (top, bottom, left, right). Along with the azimuthal data, average values for each parameter are also available.
The ADN provides azimuthal borehole compensated formation density, neutron porosity and photoelectric factor measurements. Given present technological capabilities, estimations of bulk porosity and permeability are best made by in situ borehole measurements, preferably at scales large enough to average the effects of irregular fracture porosity and matrix porosity. ADN measurements allow both for determining matrix and fracture porosity and locating overpressure zones.
The Power Pulse (MWD) tool can measure parameters such as annulus pressure, torque, and penetration rates. Together, MWD and ADN can render reliable measurements of effective pressure through both normal and overpressurized zones. If overpressurized zones exist within a fault zone, the magnitude and effects of fluid pressure on fault displacement and fluid flow can be assessed by estimating the amount of fluid expulsion (porosity reduction) in the immediate vicinity of the borehole.
Fault collapse and strain hardening, active fluid flow, fault-fluid interactions, and the formation of hydrofractures may occur within fault zones. Variations in fault displacement and fluid activity can be related to the in situ measurements to investigate the degree to which these processes are active. The ADN measurements of porosity and estimations of fluid pressure can illustrate the nature of the pressure seals as well as the physical processes responsible for fluid migration and redistribution along a fault zone. The determination of the Vp and bulk modulus using ISONIC and ADN data can also contribute to the understanding of the mechanical strength of the rocks within and near a fault zone. These LWD azimuthal measurements can be used to provide information regarding the spatial variation of physical properties around the borehole.
The ADN measurements can also provide porosity information as a function of borehole azimuth. To estimate strain from in situ porosity, lithological effects on these measurements must be first distinguished from the porosity effects. For this purpose, RAB resistivity and gamma-ray measurements can be used to estimate any significant changes in clay mineralogy within a fault zone. Laboratory porosity measurements and thin sections of core samples allow observations of interstitial pore structures and can serve as a correlation tool for more refined calculations of continuous porosity records from the log data. The porosity and resistivity image data can provide information about fracture density, fracture aperture, and structural orientation in the vicinity of the hole. In addition, these data may be used to distinguish fractures that are transmissive from those that are not.
Laboratory measurements and mathematical modeling have been used to define the density and photoelectric response and to quantify environmental effects. These effects include gamma ray streaming, mud weight, tool standoff and photoelectric effects of formation and mud on density.
A reliable density measurement requires good contact between stabilizer and formation. Because a statistical caliper measurement is made during the recording, it is possible to check the quality of the contact. Contact also affects the neutron log response; the formation signal, particularly for the epithermal count rates, tends to be masked by the borehole signal with increasing hole size.
(This tool has not yet been deployed by ODP Logging Services, so we have no examples at this point.)
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Tool weight:
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2000 lbm (907 kg) |
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Tool length:
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21.7 ft (6.62 m) |
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Min. - Max. temp:
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-13° - 300°F (-25° - 150°C) |
| Collar OD: |
6.75 in API tolerances |
| Stabilizer OD: |
8.25 to 9.875 in. |
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Maximum weight on bit:
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F = 74,000,000/L2 lbm (where L is the distance between stabilizers in feet) |
| Maximum overpull (no bending): |
330,000 lbf |
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Maximum operating pressure:
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20,000 psi |
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Maximum flow rate:
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800 gal/min |
| RHOB |
Bulk Density (g/cm3) |
| DRHO |
Bulk Density Correction (g/cm3) |
| PEF |
Photoelectric Factor (barns/e-) |
| TNPH |
Thermal Neutron Porosity (%) |
| DCAL |
Differential Caliper (in.) |
| ROMT |
Max. Rotational Density (g/cm3) |
| DPOR |
Max. Rotational Density Porosity (p.u.) |
| HDIA |
Horizontal Diameter (in.) |
| VDIA |
Vertical Diameter (in.) |
| NTCK |
Neutron Detector Sample Depth Tick Mark |
| DTCK |
Density Detector Sample Depth Tick Mark |
| ROP |
Rate of Penetration (ft/hr or m/hr) |
| TAB |
Time After Bit (hr or min) |
* ®trademark of Schlumberger |
