Well Logging In Extended-Reach And Horizontal Boreholes

Abstract

In greater than 60Deg. angle wellbores and in less deviated wells with poor borehole conditions, special hardware systems are required to guide, push, or pump the logging tool assembly toward the bottom, i.e. the end of the wellbore and to log the interval of interest. Three pipe-conveyed logging (PCL) systems are discussed, all of which use 8-conductor wet connector, side entry sub, and full-sized standard well logging instruments. The connect PCL system has the logging assembly in a tool-specific special protective housing (e.g. fibreglass sleeve, full metal or slotted metal housing), which is attached directly to the drillstring. An orientation sub monitors the position of pad-type devices in the wellbore. With the PCL system, the logging tools are run in a protective rigid metal housing and firmly connected to the drillstring. The wet connector and latching assembly are run on the wireline cable into the drillship through the side entry sub. Once connection is made and the drillpipe lowered to the zone of interest or total depth (TD), the logging assembly is unlatched and extended outside of the protective housing. Logs are obtained by tripping the drillpipe out of the borehole. In the direct-connect PCL system, the logging assembly is attached directly to the drillpipe without protective housing. A force gauge and shock sub are placed in the logging tool string, however, for added protection. Furthermore, a coiled-tubing-conveyed (CTC) system for logging and perforating applications in extended reach and horizontal wellbores has recently been developed and already proven successful in Europe, Alaska, California, etc. The present paper discusses these basic hardware systems, illustrates applications, and reviews possible constraints of each of these technologies.