Description
The A-One Oil Variable Density Log (VDL) is a specialized acoustic logging solution designed to deliver highly detailed, waveform-based insights into cement bond quality behind casing in oil and gas wells. As an integral component of cement evaluation workflows, VDL complements traditional cement bond amplitude logs and provides engineers with a more qualitative and visual representation of cement integrity for zonal isolation and well integrity planning.
What Is a Variable Density Log (VDL)?
A Variable Density Log (VDL) uses sonic measurements acquired after primary cementing operations to visualize the full acoustic waveform response recorded by a downhole sonic tool. Instead of focusing solely on amplitude or transit time, the VDL displays acoustic waveforms as a density plot (shades of gray or color scale) over depth - effectively creating a "waveform image" of bond conditions behind casing.
This waveform-based visualization helps interpreters detect features such as:
◆ Micro-annuli or thin gaps between casing and cement.
◆ Channeling or voids in the cement sheath.
◆ Cement-to-formation coupling quality
Effects of gas, fluid, or formation conditions on acoustic response.
Technical Parameters
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General Specs |
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Pressure Rating |
14,500psi (100Mpa) |
14,500psi (100Mpa) |
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Temperature Rating |
350°F (175℃) |
350°F (175℃) |
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Minimum Casing Diameter |
4.5" (114mm) |
4.5" (114mm) |
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Maximum Casing Diameter |
10" (254mm) |
13-3/8" (339.7mm) |
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Diameter |
2-3/4" (70mm) |
3-11/20" (90mm) |
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Length |
2680mm(105.5in) |
2750mm(108.3in) |
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Weight |
44.6kg |
67kg |
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Logging Speed |
32ft/min(10m/min) |
32ft/min(10m/min) |
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Joint Connection |
13-core |
13-core |
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Logging Conditions |
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Well Fluid |
Oil, Fresh Water, Salty Water |
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Position |
Center of Casing |
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Sensors Parameters |
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Transmitter |
1 |
1 |
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Receiver |
2 |
2 |
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AD Resolution Ratio |
12 bit |
12 bit |
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AD Acquisition Ratio |
10Mps |
10Mps |
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Source Distance |
8-sector probe |
12-sector probe |
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CBL Probe |
CBL Probe |
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VDL Probe |
VDL Probe |
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Electrical Characteristics |
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Voltage |
15 to 30 VDC |
15 to 30 VDC |
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Current |
80mA@20VDC |
80mA@20VDC |
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Sampling Period |
320ms |
320ms |
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Transducer Parameters Memory Capacity |
20KHZ 10Gb |
20KHZ 10Gb |
Why VDL Matters for Cement Evaluation?
Ensuring effective cement bonding between casing, cement, and formation is a cornerstone of well integrity. Poor cement bond quality can lead to:
◆ Zonal communication and unwanted fluid migration
◆ Compromised well barriers during production or injection
◆ Regulatory non-compliance and increased operational risk
While traditional Cement Bond Logs (CBL) provide quantitative amplitude data, VDL offers graphical insight into acoustic waveform patterns, helping seasoned interpreters recognize subtle bonding issues that may not be evident from amplitude alone.
Operational Uses of VDL
The Variable Density Log plays a supportive yet critical role across various phases of well operations:
◆ Post-Cementing Evaluation
Provides a detailed sonic assessment of bond quality immediately after cement placement.
◆ Pre-Perforation & Completion Planning
Ensures strong cement bonds before perforating zones for production stimulation.
◆ Workover & Well Integrity Audits
Used in remedial planning when bond quality needs re-assessment during well intervention.
Advantages of Variable Density Log
◆ Enhanced qualitative insight beyond simple amplitude measurements.
◆ Visual representation facilitates intuitive interpretation.
◆ Detects subtle bond defects like micro-annuli and channeling.
◆ Complements standard CBL data to build a richer dataset for decision-making.
By aligning Intuitive explanatory diagram with known acoustic physics and downhole conditions, VDL enhances interpretation quality while leveraging established sonic logging principles.
Reliable and Insightful Cement Evaluation
The Variable Density Log (VDL) is a scientifically grounded and practical tool in the suite of cement evaluation technologies. It provides operators and service companies with Intuitive explanatory diagram insights that enrich and qualify traditional cement bond metrics. With careful deployment and expert interpretation, VDL helps ensure that cement jobs meet engineering expectations and regulatory requirements-ultimately safeguarding well integrity and optimizing production performance.
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