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TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe Chirag Field, located offshore in the Caspian Sea of Azerbaijan, uses permanent downhole gauges to record continuous pressure and temperature in the active producers. Bottom-hole pressure data is used extensively to understand interwell communication and reservoir properties, but bottomhole temperature data had seen little use. However, we now find that flowing bottom-hole temperature detects interwell communication -with interference delay times consistent with pressure transient analysis -and can be used to estimate interwell permeability. To explain our observations we propose that FBHT responds to the impact of pressure changes. The principal result is a change in the producing GOR, which in turn depends on the speed and magnitude at which a pressure change is transmitted through the reservoir. The effect is pronounced when flowing pressures are below bubble-point and compounded by Chirag's steeply dipping reservoir having gradients versus depth in saturation, temperature, bubble-point, and solution-GOR. Field examples highlight the strong cause-effect relationship between producer-injector and producer-producer pairs, giving evidence of a new interference testing method with wide potential application. Chirag FieldThe Chirag Field in Azerbaijan (Fig-1 and 2) is located offshore in the Caspian Sea. It is part of the Azeri-Chirag-Guneshli (ACG) development and the principal production zone is the Middle Pliocene Pereriv sand. There are currently ten producers and six peripheral water injectors active in Chirag. Production, exported through the Baku-Tblisi-Ceyhan (BTC) pipeline, is 140 Mstb/D with 900 GOR (scf/stb) and less than 1% watercut; water injection is 140 Mbw/D. The structure is an elongated anticline with dips of up to 45 degrees, an overall hydrocarbon column height of up to 1000 meters, and an average stratigraphic thickness of 130 meters in the Pereriv. The two most permeable intervals, the Pereriv-B and Pereriv-D, have a total thickness of 80 meters with 20% porosity and 200 md permeability.

Accurate and timely information is essential to monitor, control and manage reservoir and well performance. At the present, production and reservoir engineers as well as production geologists have a challenging task of managing oil and gas reservoirs. This requires a broad knowledge of the reservoir supported by fit-for-purpose integrated technologies and real time access to relevant data. In the Azeri-Chirag-Gunashli (ACG) field development, downhole information is commonly acquired through uses of LWD (logging while drilling) tools to obtain a standard log suite and obtain formation pressure measurement, production logging and well testing. In addition, Downhole Temperature Sensors (DTS) has been installed on someACG wells to provide continuous temperature readings across the reservoir so as to obtain critical understanding of reservoir behaviour, connectivity and fluid distribution.ACG structure is located in the offshore of Azerbaijan part of the South Caspian Basin (Figure 1). The structure is an elongate anticline with 3 main accumulations ( Figure 2): 1). Shallow Water Gunashli (SWG) is in the northwest operated by SOCAR and on production since 1980; Deep Water Gunashli (DWG) extended from SWG to the east and became a part of ACG field operated by AIOC with production start-up in 2008; 2). Chirag situated in the centre of the structure that has been on production since 1997; 3). Azeri is in the south east which is in production since 2005(Wethington et al., 2002. ACG structure is complicated by the presence of several mud volcanoes and series of faults and seismic elements cutting field along the length. Development of field is under 30 years PSA that expires in 2024.This field contains 16 hydrocarbon-bearing reservoirs of Pliocene age. Each of the reservoirs is regionally identifiable, laterally extensive and correlatable within the long distance. They comprise stacked fluvial-deltaic sandstones deposited by the paleo-Volga delta, flowed from the north to the south into the lacustrine South Caspian Basin.The main producing interval in Azeri field is a Fasila reservoir that has been subdivided into 5 sublayers (Fasila A,B,C,D, & E) based on the first appraisal well stratigraphy. A stratigraphic section of Fasila reservoir from one of ACG wells shown on Figure 3 illustrates high net-to-gross (NTG) Fasila B and Fasila D sublayers separated by lower NTG Fasila A, C and Fasila E layers.Azeri development proceeds under crestal gas and peripheral water injection support. Therefore understanding of compartmentalization of the structure plays significant role in production efficiency.

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