Field Experience with a New Carbon/Oxygen Logging System in Complex Wellbore and Formation Conditions

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractCarbon/oxygen (C/O) tools have been designed for helping evaluate reservoirs under relatively simple conditions, such as cased wells with tubing removed and a single fluid present and reservoirs that have relatively high formation porosity. However, to reduce costs, tubing is often not pulled and wellbore conditioning is minimized. A new generation of small-diameter C/O tools capable of logging through-tubing has therefore been developed to deal with these circumstances. Logging through-tubing, despite its advantages, presents its own set of problems. Obtaining reliable measurements is often highly challenging because of different tubulars, various borehole fluids, and multiple contacts in a single well.A new high-resolution C/O system has recently been developed for use under such complex conditions, specifically in tubing of 2 7 / 8 -in. and larger diameters with various fluids in the tubing/casing/formation. The tool has been run successfully in borehole conditions with wells flowing and shut-in. Sometimes the conditions included multiple wellbore contacts of gas, oil, and water within casing and multiple contacts in a tubing/casing annulus. Despite the various and changing borehole environments encountered by this tool, advanced electronics and detector designs, careful characterization, and comprehensive software have resulted in high-quality measurements.This paper illustrates performance of the new C/O system under extremely inhospitable conditions in the Asia-Pacific area. Conditions include multiple contacts with water, oil, and gas in the borehole, as well as multiple contacts with water, oil, and gas in the tubing/casing annulus. Furthermore, reservoir porosity in the subject borehole was in the low range of 8 to 15%, where success with C/O logs has previously been minimal. Nevertheless, the tool obtained extremely useful data that provided an accurate assessment of the reservoir conditions, and thus allowed decisions to be made for secondary workovers and other reservoir product management remedies.

Evaluation of Behind-Pipe Saturation in a Miscible CO2 Flood

“…The technique is a three stage process. First, an initial estimate of oil volume (V oil , 0 ) is made, assuming a two-phase saturation, by using (Simpson et, al., 2001) 3 7 ) where, C hc is the carbon index of the aggregate hydrocarbon, and it is a volumetrically weighted sum of the individual components given as (Simpson, et, al., 2001) gas oil…”

“…The second step in the process was to use a three-phase response equation to solve for the volume of gas (V gas ), incorporating the (imperfect) initial oil volume estimate (Simpson, et al, 2001). …”