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Abstract Over the past 2 years, a number of tractor-deployed wireline operations have been performed by Total EP Qatar on Al Khalij field, ranging from Corrosion evaluation, ballistic operations to Production Logging operations in various casing sizes and environments. Typical Al Khalij wells feature long to very long horizontal sections, ranging from several hundred meters to 3,350m, most of them cased with cemented and perforated liners. Besides, Al Khalij oil wells are produced with downhole ESPs (Electrical Submersible Pumps), which make the acquisition of downhole production data a real challenge. Owing to the above factors, the use of conventional deploying techniques of logging tools (such as coiled tubing) is not possible. With the increasing maturity of downhole wireline tractor technology (Fig.1), performing the necessary wireline cased hole acquisition in such environment has now become possible. The paper presents the various applications of this technique on Al Khalij field. It also demonstrates that the candidate wells feature horizontal sections that are amongst the most ambitious for the application of the wireline tractor technique. Main Operator and Contractors' findings are also described. Finally, some recommendations are presented in order to make the application of wireline tractor-deployed operations a success story. Field Presentation The Al Khalij field lays 100km offshore Qatar in 60m water depth. The first discovery dates 1991, when the Mishrif reservoir was confirmed oil bearing. First oil was delivered in 1997 and the field was developed in three phases now completed. End 2005, the field development engaged in an infill drilling phase. Today this vast field is produced through 7 unmanned wellhead platforms and 1 water separation platform. The total output of the field is 190 Kbpd of liquids, and approximately 40 Kbopd. A total of 34 oil producers, 6 water injectors and 4 water producers, have been drilled and completed to date. Due to the proximity of the aquifer, significant amounts of water are produced. The current water cut of the field is 75% (mid 2007). Owing to the sub hydrostatic reservoir pressure, producer wells are equipped with Electrical Submersible Pumps (ESP's). The electrical generation necessary to power the ESP's is located on Halul Island, located 45 km away from the field (Fig.1). Most of the water produced is separated offshore on a process platform and is reinjected in the field with the water injectors wells aiming at sustaining reservoir pressure. Additional water is produced from the Umm Er Radhuma shallow aquifer and reinjected into the Mishrif reservoir in order to achieve a full voidage replacement and further sustain reservoir pressure (Ref.1 and Ref.2). The Mishrif carbonate reservoir displays several thin producing stacked layers (3 to 5 meters thick) which display a wide range of permeabilities (from 5 to 300mD). In order to increase the Productivity Index and the drainage area of the oil producer wells, they usually feature long to very long cased horizontal drains, amongst the most ambitious ones in the industry. Nearly all wells drilled after year 2000 feature drain lengths in excess of 2000m (Fig. 2: plot of the Al Khalij drain lengths). Once these long drains are drilled and cased, the most significant challenge is to stimulate them effectively. The technique used on Al Khalij field is well described in Ref.3 and Ref.4. Wireline tractors applications Injection log In most cases, skin data indicated that stimulations on Al Khalij wells were successful. But there was often little or no evidence that the full length of the very long drains effectively contributed to production. It was therefore proposed to run wireline flow-meter tools in candidate wells, while injecting brine at a constant flowrate. If the drain had been properly stimulated on its entire length, it was expected to measure an even injection rate in all perforations. On the contrary, a non-effective acid diversion would have resulted into unexplained preferred injection paths, raising concerns regarding the stimulation technique used. |
