The Tengiz oilfield is a giant, carbonate reservoir of Devonian to Carboniferous age located in the Pricaspian Basin of the Republic of Kazakhstan. Gas Injection at the Tengiz field began in January 2007 with sweet gas injection as Phase 1 of the Sour Gas Injection (SGI) pilot project followed by sour gas injection as Phase 2. Phase 2 injection began in October 2007, but was interrupted due to initial start up problems. Continuous sour gas injection was achieved three months later in January 2008.The SGI project has four signposts for success: compressor reliability, injectivity, wellbore durability, and reservoir performance. The sour gas compressor at Tengiz was the first of its kind and has had greater than 90% availability when the Second Generation Plant (SGP) has been operational (SGI injection gas is produced through SGP). Injectivity has exceeded expectations and wellbore durability has also been excellent. Reservoir performance is a longer term signpost which is monitored though an extensive surveillance program. The Tengiz Reservoir appears to be performing as expected to the sour gas injection.The SGI project is a first-contact miscible gas injection process consisting of seven inverted five-spot patterns. To expedite data acquisition, the SGI well patterns were designed to include one "super-spot" pattern (twin injectors 100 m apart providing dedicated injection support to different geologic layers) and three short-spaced producers (producer-injector spacing approximately 1/3 of the standard spacing). Tracers, pulse tests, multiphase meters, gas saturation logs, and production and injection logs are used to monitor and understand reservoir performance. A specialized simulation model (the SGI Monitoring Model) was constructed which uses local grid refinement in the SGI pattern area. This model is used to determine how well the reservoir characterization is able to capture the dynamic reservoir response to the miscible SGI process.An earlier paper (Darmentaev et. al., 2010) discussed preliminary results from the SGI project. The proposed paper will discuss recent results from the reservoir surveillance program, how these recent results compare to the preliminary results, and the integration of all results into our current understanding of SGI performance. In addition, updates to the Monitoring Model, lessons learned and best practices developed since the commencement of sour gas injection will be discussed.

Over the field life, surveillance in Tengiz oil field has provided historical and baseline data for simulation history matching, static and dynamic reservoir characterization and modeling, and the foundation for efficient well management. Hence, it continues to be an important part of everyday field operations. At the surveillance planning stage, the comprehensive opportunity list of well candidates is developed based on input provided by members of multiple teams: geologists and petrophysists, production and reservoir engineers, drilling and field operations specialists. SCADA system, permanent downhole gauges (PDHGs) and multiphase flow meters (MPFMs) are widely implemented for production data acquisition and analysis. However, the majority of surveillance activities still need well intervention into the high pressure, high H 2 S concentration wellbores, often during harsh weather conditions. Each job execution plan is therefore focused on the safest procedure to obtain the necessary data. Each planned survey in the surveillance plan is ranked according to the value of information to be obtained, in order to help schedule the timing of surveillance based on plant production needs.The ultimate goal is to safely execute planned surveillance to support production optimization and field development work. This paper will highlight TCO success in addressing the different reservoir and well production uncertainties through a properly designed surveillance plan with both short and long-term objectives.

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A new approach in advanced multiphase metering methodology designed for use in sour fields, quantifying H2S content in flow and properly accounting for it in the different phase rate measurements is presented. Flow metering in sour fields is challenging due to the need for containment of produced fluids and the effect of fluid properties in the interpretation of the measurements. The addition of H2S measurement provides additional information for production and reservoir monitoring and also yields improvements in flow metering, accounting for variations in fluid properties used for multi-phase calculation. Multiphase Flow Meters (MPFM) utilizing multi-energy gamma-ray fraction measurements are based on the ability of oil, gas, and water to absorb gamma rays of two different wavelengths. Adding an extra measurement at a third level of energy and leveraging the large contrast between the attenuation of sulfur and that of hydrocarbon and water components makes it possible to determine the mass fraction of H2S as an additional output. This technique was applied in Tengiz field, Kazakhstan, characterized by a high H2S content. In order to maintain reservoir pressure, improve recovery and utilize produced associated gas, a sour gas miscible flood pilot was started in 2007. The monitoring of compositional variation in producers is critical in the understanding of solvent (sour gas) distribution and thus in managing production-injection patterns to optimize plant throughput. Early field trials of the method were made comparing metered H2S content with surface PVT samples, confirming the accuracy of the methodology. The technology was then implemented systematically but strategically across the field. The in-line H2S measurement with automatic updates for variation in fluid properties was applied in two distinct areas: within the sour gas injection pilot area, where solvent levels vary, and outside the area where hydrocarbon composition is known to be homogeneous and constant. Long and short term tests with multi-rate well tests were conducted. Full datasets were collected from the MPFM to evaluate measurement stability and representativity under different flowing conditions and compared to results obtained without accounting for compositional changes. The results show a stable, accurate and continuous measurement of H2S content in produced fluid and an enhanced measurements of water, oil and gas rates comparable with PVT results. The in-line H2S measurement based on multi-energy gamma ray measurements is the only continuous H2S measurement technology available in multiphase flow conditions. It can be retrofitted to existing MPFMs, allowing to get additional parameter and enhanced stability of flow rate measurements where properties of produced fluid vary continuously. This paper will begin with a presentation of the theory, formulation and validation of the in-line H2S measurement and then go on to present a case history of the application in the Tengiz field, Kazakhstan for Tengizchevroil (TCO).

Авторское право 2014 г., Общество инженеров нефтегазовой промышленности Этот доклад был подготовлен для презентации на Ежегодной Каспийской технической конференции и выставке SPE, 12 -14 ноября, 2014, Астана, Казахстан.Данный доклад был выбран для проведения презентации Программным комитетом SPE по результатам экспертизы информации, содержащейся в представленном авторами реферате. Экспертиза содержания доклада Обществом инженеров нефтегазовой промышленности не выполнялась, и внесение исправлений и изменений является обязанностью авторов. Материал в том виде, в котором он представлен, не обязательно отражает точку зрения SPE, его должностных лиц или участников. Электронное копирование, распространение или хранение любой части данного доклада без предварительного письменного согласия SPE запрещается. Разрешение на воспроизведение в печатном виде распространяется только на реферат объемом не более 300 слов; при этом копировать иллюстрации не разрешается. Реферат должен содержать явно выраженную ссылку на авторское право SPE.