Optical televiewer Logging (OTV) is a type of downhole survey that uses a camera to capture images of the wellbore walls. It is also known as a borehole televiewer, borehole camera, or borehole imaging. The OTV tool is lowered into the wellbore on a wireline or conveyed on a drilling assembly, and it captures images of the wellbore walls as it is lowered. The images are then analyzed to determine the properties of the rock formation and to identify any abnormalities or features in the wellbore.
OTV can provide detailed images of the wellbore walls, which can be used to identify the type of rock formation, the presence of fractures, vugs, and other features that can affect the good integrity and the production of oil and gas. Additionally, OTV can also detect the presence of drilling mud or cement returns, which can indicate a problem with good integrity.
Optical Televiewer Logging Overview
The Optical Televiewer system consists of a completely redesigned optical assembly and electronics, and uses a high-resolution CMOS digital image sensor combined with a fisheye lens and LED lights.
The tool produces an extraordinarily sharp, continuous 360° unwrapped digital picture of the borehole wall, either in air or clear water. Resolution up to 1800 pixels over the borehole circumference can be achieved, making it ideal for lithological, mineralogical and structural analyses.
Optical televiewers function best in either dry or clear water filled boreholes, as cameras function by focusing light onto an image pickup device. If the borehole is fluid filled, it is recommended to run an optical televiewer before any other logging equipment to ensure no sediment is suspended in the borehole fluid. A mud-caked borehole wall also compromises image quality, and it may be necessary to clean the borehole wall or use a flocculant prior to logging depending on the extent and severity of the mud-cake.
A built-in high precision orientation sensor incorporating a 3-axis fluxgate magnetometer and 3 accelerometers allows orientation of the images to a global reference and determination of the borehole’s azimuth and inclination. Gyroscopic data can also be used in the processing of optical or acoustic image data if there is a strong magnetic influence while collecting the well log data (either due to steel casing or lithology).
What Does Optical Televiewer Logging Measure?
Rock Formation
OTV can be used to identify the type of rock formation, which is important for reservoir characterization and exploration.
Fractures
OTV can detect natural fractures in rock formations that can affect the flow of fluids and the production of oil and gas.
Vugs
OTV can detect the presence of vugs, which are large voids in the rock formation that can affect the good integrity and the production of oil and gas.
Cement And Drilling Mud Returns
OTV can detect the presence of drilling mud or cement returns, which can indicate a problem with good integrity.
Corrosion And Erosion
OTV can detect signs of corrosion and erosion on the wellbore walls, which can indicate a problem with good integrity.
Other Wellbore Abnormalities
OTV can detect other wellbore abnormalities such as ledges, washouts, keyseats, and other features that could compromise good integrity.
What Is Optical Televiewer Logging Used For?
Reservoir Characterization
OTV can be used to identify the presence and orientation of hydrocarbon-bearing formations, which can help in the exploration and production of oil and gas.
Well Integrity Check
OTV can be used to evaluate the condition of the well and detect any signs of damage or deformation, which can cause well integrity issues.
Completion Design:
OTV is used to design the completion string and select the appropriate size of the casing and tubing, in order to ensure a proper fit and avoid wellbore collapse or other issues.
Fracture Detection
OTV can detect natural fractures in rock formations that can affect the flow of fluids and the production of oil and gas.
Drilling Optimization
OTV can be used to optimize drilling parameters such as weight on bit, rotary speed, mudflow, and mud properties, to improve the drilling efficiency and reduce the risk of wellbore instability.
