The Road to Achieving Business Value With Reflection Sonic Imaging

Reflection sonic imaging has been around for decades. However, there are still open questions on the range of applications and what can be really taken to the bank to impact our business challenges. Clear imaging of faults, fractures, overturned beds, and abrupt changes in structure are all of interest to those hoping to understand the bigger geologic picture away from the well. Guiding drilling in horizontal wells with real-time sonic imaging of reservoir boundaries is another prize that has not yet been achieved but needs to be firmly on the radar. In this paper, we concentrate on dipole-induced shear wave imaging and show an example of imaging reservoir boundaries in an extended reach/horizontal well acquired by a drillpipe-conveyed slimhole crossed-dipole sonic tool. An additional effort shows the investigation of fracture imaging in data from several wells, with a goal to establish under what conditions fractures can be imaged from a wellbore. A new reflection sonic imaging workflow was developed and is applied to dipole-induced shear waves to the image structure of interest. In a manner like seismic imaging processing, a key component of this workflow is the generation of a multidimensional velocity model in earth coordinates that is used for the prestack migration of the reflection sonic data. The model can then be iteratively updated using reflection sonic imaging results. Another key part of the workflow is identifying specular reflections from the structure of interest in the time domain before applying any imaging algorithm. Prestack migration is then applied, and then the process is iterated to ensure that a better image result is achieved with any time-domain data processing step. Imaging of sonic data acquired in an extended reach/horizontal well details high-resolution images of the reservoir boundaries relative to the well. It was found that simple treatment of the received data and an automatic migration processing flow were sufficient to achieve the key objectives of imaging these boundaries. Here the potential business value impact is that imaging results may be delivered in time to affect well decisions such as where to frac the well. For fracture imaging, results, where attainable, show high-resolution displays of the fracture topography and so delineate the actual tortuous path of the individual fractures away from the borehole. Preliminary results show that the best images come from large individual fractures or groups of aligned fractures with insufficient signal for imaging resulting from low aperture fractures or multiple fractures at different orientations. Ongoing research is looking to establish initial guidelines for imaging fractures based on effective fracture width and other considerations. On the road ahead, thoughts on what needs to be in place for routine business value to be achieved will be presented, including desired technology advancements. On the business side, a key question for end users is this: “What would we do differently with the information from this image?” To answer this question, essential is involvement by multidiscipline asset team specialists, including petrophysicists, geologists, and seismic interpreters, to integrate sonic imaging into their workflow.