Material balance analysis, a primary engineering technique, is an indispensable tool used for understanding the production performance and field management of mature gas reservoirs. Compilation and analysis of pressure-production data together with acomprehensive geological understanding including in-place hydrocarbon volumes and inter-block communication are prerequisites for material balance analysis. Deviation of observed P/Z data away from a straight idealised line necessitates further study, as it often indicates erroneous estimates of participating in-place volumes, aquifer support or reserves. Lack of pressure measurements, questionable stratigraphic correlations and uncertainty surrounding aquifer propertiesor reservoir connectivity highlight the requirement for further evaluation. The objective of study is to develop a multi-tank material balance modelfor a mature, heterogeneous and compartmentalised carbonate gas field. Ultimately, the model must besufficiently robust to elucidate the field's production mechanism and optimise future field-development opportunities. In this field, the pressure production behavior can be divided into two trends, an early rapid declining pressure trend, followed by a stabilised gradual pressure decline. Owing to higher drawdown in the field's early production life and insufficient recharging, the quick pressure decline underestimates the initial in-place gas volume. This volume is not adequate to support the sustained gas production rates observed in later years. This observation required further detailed analysis regarding the nature of zonal communication across adjacent reservoir intervals to better understand the production behavior of development wells during the design of the material balance model. This paper discusses a study in which material balance analysis is coupled with multi-field network models. Implementation of this workflow can be usedto drive subsurface developmentsin a relatively short period.

Production data analysis (PA) refers to all analytical approaches and tools to reveal reservoir properties, performance, and characteristics such as material balance, Flowing Material Balance (FMB), Pressure Transient Analysis (PTA), Rate Transient Analysis (RTA), Decline Curve Analysis (DCA) and deconvolution. PA provides robust information comprising reservoir container volume, depletion mechanism, reservoir connectivity and well performance. It provides the best view on reservoir performance and helps to characterize the reservoir to understand reservoir quality, boundaries and flow characteristics to develop and optimize current reservoir management prior to any dynamic modelling. In this paper, the focus will be on analytical methods such as Rate Transient Analysis (RTA), Flowing Material Balance (FMB), Pressure Transient Analysis (PTA) and analytical simulation as an integrated approach for enhanced production data analysis in Gas fields. The idea of FMB has been introduced by L. Mattar (1997) and it is generally applied to determine oil or gas in-place using flowing pressure data (L. Mattar and Anderson, 2005). The main objective is to show the methodology for production data analysis, illustrate its added value to reservoir performance monitoring as well as its advantages for well-test design and production forecasting. The results show that different approaches need to be used consistently to enhance the reservoir characterization and improve reservoir understanding in using production data prior to full field dynamic application. Integration helps to resolve uncertainties quickly and economically.

In a complex offshore gas network covering both green and mature fields' production to LNG plants, end-to-end integration is essential in building a portfolio that can maintain output. Often in the course of identifying conceptual development opportunities by individual field, this aspect isoverlooked in the broader context of regional optimization. To provide assurance of production sustainability to meet commercial agreement, it is imperative to formulate a development plan that integrates subsurface and surface elements to accurately quantify the remaining reserves and thus the value of the asset. As such, this paper will focus on the methodology of formulating this optimized development plan to incorporate subsurface and surface network modeling and demonstrate the importance of this system for excellent asset management and future development. A series of reservoir evaluations has been performed on a simple one-dimensional model and three-dimensional model depicting the gas reservoir performance. The analysis is further enhanced by using subsurface and surface production network modeling. The key advantages of this workflow compared to the conventional field development plan (FDP) approach is that the field capacity is derived based on pressure interface and existing production constraints to capture any backpressure effects for anyinfill drilling or upgrading projects. In this field example, the integrated network model has resulted in a simpler yet more reliable technical proposal where synergistic opportunities and the associated potential production challenges can be identified.Higher level goals on production attainment and cost avoidance can be achieved through circumventing the potential production hiccups for new development. A detailed analysis workflow using real time data will be discussed as part of technical assurance.The key benefits include full field optimization and opportunities identification,and generation ofa representative business case in a timely manner to meet the demands of managing a dynamic gas system.

BY, an offshore oil field discovered in 1976, has been in production since 1984. Several production enhancement activities were continuously conducted throughout the production life of the field. This includes surveillance works to arrest the production decline and enhance the oil recovery. A systematic investigation showed that a few wells were having anomalous high water production despite being located at the crestal area of the reservoir. Further investigations revealed that poor cement bonding behind the casing was the main cause of high water production in the up-dip wells. With this new information, an evaluation of the remaining reserves was carried to justify any remedial well work required to reactivate the wells. A coiled tubing cement squeeze job was identified at BY field to unlock the well potential of the watered out well located at the crest of the reservoir. The well, WELL-X has been idle for over 20 years due to high watercut. After a successful job execution, the well was able to flow with more than 1000 STB/D at 0% water cut. This has opened up more opportunities for idle well reactivation of other idle wells with similar high water cut due to cement channelling issues behind casing. This paper presents an established workflow and optimization cycle adopted in BY highlighting the methodologies/techniques used to identify potential production opportunities that may have been overlooked in a brownfield and a recommendation on the way forward. The systematic workflow applied displayed success in a well using rigless intervention and has achieved economic return in a short time.