The term cased hole service refers to the geophysical investigation of the borehole after the completion of a well and is generally either a PVC or steel material. In instances where an existing cased well is in need of evaluation tools can be lowered into the well to evaluate where screened intervals are located, or to assess the same geological boundaries of sands and clay members. A simple Gamma Ray survey can provide this detailed information; however the curve itself may be “shielded” a little due to the presence of the casing and grouting materials that will impede the returned data as compared to an open hole survey where there is nothing between the tool and the formation being evaluated. Sometimes a combination of Gamma Ray and Resistance tools can determine where a casing may be split, or as a result of connections in the casing leaking as the tool will “log resistance data” at the leaking interval as the leak provides a way to complete the electrical circuit to a ground plug at the surface.
Instances where water quality may be a concern can be due to differential hydrogeologic aquifer pressures between confined aquifers that may be cross feeding from one to another causing a mixing of groundwater fluids. This determination may be assessed through the application of a Full Wave Sonic Tool. The sonic tool uses acoustic transmitters and receivers to evaluate the integrity of the cement grout to the casing and the borehole wall. The benefit of this allows engineers to determine the quality of the cement application itself and to iensure the formations are sealed to prevent cross tubing of fluids; while ensuring the fluids pumped out of the wells are from the intended zones of interest. This is also known as cement bond logging, or CBL.
Instances exist where a historic well has vertically migrated due to various reasons and a deviation study can be executed to assess how far a well casing has migrated from the original vertical completion. Casing collar locators and calipers are also beneficial in determining the locations of casing joints and engineered well structures to better evaluate well conditions downhole. TeaCo also offers a color digital camera of various qualities to image the inside of casings when looking for leaks, breaches, or even screens.
Contact TeaCo today for a complete offering of available tools designed for the geophysical well logging requirement of your projects! We look forward to hearing from you.
CBL & Optical Televiewer