Logging tools using real-time transmission systems are now capable of imaging the wellbore as it is drilled.

Although, logging and measurement while drilling (LWD/MWD) tools have been available for many years, it is only recently that advances in data transmission and interpretation have progressed to generate accurate images of the wellbore. These images are based on real time data and offer insight into what is really happening downhole.

Typically, a high quality image is drawn from detailed, three-dimensional resistivity data. This data is supplied by a resistivity tool similar to a logging formation micro-imager, which is run on wireline. The resistivity tool is capable of identifying wellbore features and characterizing faults, cementation changes and threaded or spiraling caused by bit whirl. Software transforms the resistivity data into images of 3-D wellbores that are viewable at all angles with simple mouse movements. The resistivity measurements are transformed into 56 azimuthal sectors around the circumference of the wellbore to provide extremely detailed images.

Schlumberger drilling engineer Chris Lenamond said, "Gone are the days of just more data dumps that need processing and advanced interpretation expertise before decisions can be made. The technology has now arrived where we can improve geological steering while drilling. Today's software and MWD telemetry systems provide real-time answers about 3-D wellbore features while drilling, well placement within the reservoir, wellbore stability issues, formation dip and structural configurations."

The combination of resistivity and density services based on real-time logging images and geo-steering techniques is likely to enable operators to reduce risk and overcome geological uncertainties commonly associated with complex wells.

Ultra high telemetry rates (12 bits per second) have been successfully used to optimize horizontal well placement as well as warn of wellbore stability issues before they become serious enough to jeopardize operations or impact drilling costs.

Augusto Silva, Schlumberger measurement engineer, said, "The ability to transmit high quality real-time azimuthal and image log data is possible even in cases where penetration rates are high. The resistivity images shown in Figure 1 are transmitted uphole presenting the wellbore in four quadrants. This information can be wrapped into a 3-D image of the wellbore, which assists in optimizing well placement using geological markers. Adjustments to the wellbore trajectory relative to geological bedding planes or faults can be quickly determined and steering changes are made while drilling."

Wellbore stability problems are detected with ultrasonic calipers from density logging while drilling (LWD) tools. Hole enlargement or washouts can be identified while drilling or during subsequent trips. This is beneficial as it helps monitor wellbore stability and allows adjustments to be made to mud weights or effective circulating density as required. Wellbore stability problems are confirmed using vision technology incorporating Azimuthal Density/Neutron viewer software, which provides density image and caliper data while drilling. The software also generates 3-D images and caliper logs. Together, these offer easier methods of understanding well bore conditions during drilling operations. Additionally, the 3-D density images and ultrasonic caliper allow wellbore instability mechanisms to be better characterized, and when necessary, resolved. This is particularly important in completions where gravel packs or expandable screens are required. The ultrasonic and density caliper information gathered during drilling can indicate whether hole quality is good enough to permit specialized completions to proceed. While an up log obtained on a subsequent wiper trip allows visualization of the hole enlargement and stress failures after drilling.

Specialized software uses a recorded mode to gather real-time dip information, provided by the LWD resistivity imaging tools. This information is harnessed to view geological structures and reduce the uncertainties in pre-existent geological models. Analysis of surface seismic can also help indicate the possibility of erosion surfaces, which can jeopardize well navigation. Specialized data transmission from the rig site allows continuous observation of the wellbore to anticipate changes in the bedding plane and structure behavior of the reservoir.

The software also allows structural dip picking from images, which can be used in combination with the real-time data for structural interpretation. Bed dips and layer thickness are also characterized permitting the evaluation of structural cross-sections. The reduction in risk and geological uncertainty will make the advent of wellbore imaging hard to resist for production companies.