Acquiring High-Resolution Images While Drilling in a Fast Logging Environment Utilizing a New Ultrasonic Sensor

Abstract

Abstract Fractures play a significant role in evaluation of carbonate reservoirs, where understanding the fracture type and networking is a key to evaluating their impact on the porosity-permeability relationship. The presence of fractures also increases the likelihood of having partial or total loss of circulation, which has a direct impact on drilling operations. Carbonate reservoirs are known to be laterally heterogenous. The sensors utilized were basic formation evaluation sensors (gamma ray, resistivity, density, and neutron porosity) combined with an ultrasonic imaging tool, which was utilized for the first time in the field. The ultrasonic sensor uses four transceivers that operate in a pulse-echo mode. Firing simultaneously, the transceivers provide a total of 2,000 travel-time and reflection-amplitude measurements each second, enabling the creation of high-resolution images at high logging speeds. The image can be acquired in multiple modes, while drilling and pulling out of hole, to enable the evaluation of time-dependent changes in the formation. Drilling parameters are optimized to ensure that a high-quality image is acquired while drilling by minimizing the vibration and optimizing the ratio between the rotational speed and rate of penetration. The case study was a 4,200-ft lateral section drilled using water-based mud. The reservoir had varying thickness of 13 to 27 ft, dipping in a south-easterly direction. The high-resolution amplitude image provided an understanding of fracture mechanisms within the local reservoir sector as well as highlighting asymmetric features and bedding planes. Transit-time analysis facilitated detailed evaluation of borehole size and shape, as well as providing principal stress orientations. Bed-boundary dip interpretation and secondary porosity evaluation, in terms of fractures and vugs, were useful for a better understanding of the geological setting and lateral variation of petrophysical parameters leading to reservoir characterization. The ultrasonic sensor has been shown to provide high-quality and high-resolution images at fast logging speeds. The tool provides both travel-time and amplitude images, which can be integrated for identifying the fracture type and revealing important information about the borehole shape and deterioration.