FIELD TEST RESULTS OF A NEW HIGH-RESOLUTION, DUALPHYSICS LOGGING-WHILE-DRILLING IMAGING TOOL IN OILBASE MUD

摘要

Borehole imaging at the time of drilling has beenavailable since the first azimuthal tools were designedand put into use in the 1990s. In water-base muds(WBM), numerous improvements in both the resolutionand quality of images have been made, particularly inmicroresistivity logging tools. The challenge to extendthese capabilities to oil-base mud (OBM) has beenaddressed in a new tool designed to acquire highresolutionimages in the logging-while-drilling (LWD)environment. The data are maximized by a dual-physicstechnique using separate resistivity and ultrasonicimaging sensors.The new tool is introduced along with the key designfeatures that overcome the challenges associated withLWD imaging in oil-base mud. Sensors are positionedon the rotating drill collar with resulting standoffbetween the sensors and the formation. For the resistivityimage, the tool’s electromagnetic signal must passthrough this gap which acts as an insulating layer. Highresolutionelectromagnetic pulses are sent through themud from the sensor to the formation at multiplefrequencies (similar in principle to recently introducedwireline imaging tools for OBM). A novel processingalgorithm combines the multiple individual frequenciesto produce a robust image across a wide range offormation resistivities. Two sensors are positioneddiametrically opposite each other for the resistivityimaging. Four ultrasonic sensors are positioned close tothe resistivity sensors. The high-sampling rates andfocusing of the sensors deliver a resolution comparableto wireline ultrasonic imaging tools for the ultrasonicimages in all mud types (OBM/WBM). Multiple sensorsare used for both types of physics measurement, andrapid firing and recording by the sensors maximize fullboreholecoverage in the majority of drilling conditions.An experimental version of the tool has been field testedin a broad variety of drilling and geologicalenvironments. To date, over 35,000 ft of data have beenacquired in wells ranging from vertical to horizontal.Data acquisition has been in clastics, carbonates, andevaporites having various formation properties. The fieldtest data have confirmed the metrology of both physicstypes, i.e., resistivity and ultrasonic imaging. Examplesare presented demonstrating the range of measurementsunder different borehole and geological conditions.Results to date have exceeded expectations in terms ofimaging capabilities. Moreover, the acquisition ofresistivity and ultrasonic images has frequently provedto be complementary, with the resistivity images rich inbedding features and the ultrasonic images moresensitive to fractures and borehole conditions.