Copyright 2004, Society of Petroleum Engineers Inc. This paper was prepared for presentation at the 2004 SPE/DOE Fourteenth Symposium on Improved Oil Recovery held in Tulsa, Oklahoma, U.S.A., 1721 April 2004. This paper was selected for presentation by an SPE Program Committee following review of information contained in a proposal submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Papers presented at SPE meetings are subject to publication review by Editorial Committees of the Society of Petroleum Engineers. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to a proposal of not more than 300 words; illustrations may not be copied. The proposal must contain conspicuous acknowledgment of where and by whom the paper was presented. Write Librarian, SPE, P.O. Box 833836, Richardson, TX 75083-3836, U.S.A., fax 01-972-952-9435. Abstract: Identifying the water producing section of a horizontal well completed with a slotted liner in Extra Heavy Oil (EHO) proves by itself to be a challenge. Being able to isolate that same interval and selectively injecting a water shut off treatment is even more challenging. To properly isolate the selected section, the annulars (open hole / slotted liner) above and below must be sealed; those annular may or may not be filled with formation sand. This paper describes the water shut off experience in the Sincor Field in an EHO environment. Initially, the water producing interval was identified through the use of temperature measurements performed with a fiber optic. Then the zone to be treated was isolated using cement rings placed in the annulus, combined with the use of cement retainers. Following the isolation of the zone, a gel solution that polymerizes in situ followed by a tail slurry of micro-matrix cement were selectively injected. The idea behind the treatment is to create an impermeable barrier to the unwanted water production coming from the end of the well. The well treated had an initial water cut of 85%, and after the treatment the water cut was decreased to almost zero and the oil production boosted up by a 250%, compared to hydrated production period. Additionally, the final well productivity index (PI) indicates that the treatment effectively treated only the selected section. In horizontal wells and EHO environment, the fiber optic tool proved to be a simple and reliable technology to assess the water production zone along the drain. An associated water shut off operation using cement and gel may then be implemented to reduce the water cut and to increase significantly the oil production rate. Introduction The Zuata field operated by SINCOR, a consortium of TOTAL, PDVSA and STATOIL, is one of the four strategic associations in the Orinoco Belt of Venezuela. The location of the field is shown in Fig. 1. Laying in unconsolidated sand at depths between 300 m and 500 m, the reservoir fluid is extra heavy oil with gravity ranging from 7.5 to 9 API and viscosities between 1800 cp and 3500 cp at reservoir conditions. The oil is produced by natural depletion from horizontal wells with 1400 m drain length. The reservoir fluid is mixed with a diluent in the wellbore or at the wellhead ; the diluted crude oil is then pumped to a processing center for water and gas removal. The stabilized oil is transported by pipeline to an Upgrader for further processing to produce a low sulfur high quality 32 API synthetic crude named the Zuata Sweet. The produced water is injected into the Lower Oficina aquifer. Well production history As one of the first producers, the well IB03 was drilled in 1999 in the south-western part of SINCOR area. Drilled in a massive 25 m thick sand to 2086 m (TMD), the horizontal section is 1350 m long and was completed with a 7” liner. Slot size is 20 (width 0.02 inch). Brought on production on December 17th 2000, the well produced a maximum of 2400 stb/d with a productivity index of 12 stb/d/psi approximately. After two months of production, water brokethrough. The oil production level dropped drastically to 700 stb/d of EHO with an associated water production of 1100 stb/d. The water cut rose rapidly to 60% then 80% (Fig. 2). The well was shut-in from October 2001 to September 2002. Fiber optic to detect water production zone In order to assess the water entry point, a fiber optic cable was installed in the horizontal section of the well in June 2001. The objective was to measure accurately the temperature profile along the horizontal section