Literature is replete with numerous techniques for waterflood analysis developed over the last four decades. Most of these techniques are in the form of simple diagnostic plots based on available production/injection and pressure data routinely gathered in the field. This paper illustrates a systematic methodology that integrates various diagnostic plots at field, sector, pattern and well levels. It shows the interaction between these levels and how the integration of different diagnostic techniques are key to better understand the dynamics of waterflood performance and for identification of performance improvement opportunities. The techniques presented in this paper were applied to evaluate the waterflood performance & efficiency, to identify anomalous performances, to detect production and injection problems, to establish water production mechanism, and to assess impact of reservoir heterogeneities in a giant carbonate reservoir located in the Arabian Gulf. The subject reservoir has been producing under a large scale pattern waterflood for over 30 years. The construction and uses of various diagnostic plots for quantitative assessment of the waterflood performance are presented in this paper. As a first step, the historical performance plots are used to evaluate the maturity of water production and to provide an indication of the sweep and recovery efficiency. The voidage replacement ratio (VRR) when integrated with historical pressure profiles and material balance plots provides critical information on the reservoir pressurization process. The water breakthrough time and the WOR trends are then used in evaluating the water production mechanism and in assessing the reservoir heterogeneity. Production logs (PLT, WFL, PNC, CHFR and RST) provide key information for monitoring and evaluating vertical and areal sweep in the reservoir. Hall plots provide information regarding the injection well performance and related dynamics. The approach presented above led to significant enhancement in understanding the displacement process and water movement within the reservoir. The integrated analysis resulted in improvements in the field practices for reservoir management and well completion design for future development wells.
Significant advances in reservoir management have been achieved in recent years to address the many challenges in managing giant carbonate reservoirs. The advances are made possible due to culmination of three key elements working in harmony: Work Processes, Technology and People. Three major advances mentioned in this paper underpin this all important truth in reservoir management and surveillance. First is the development and implementation of a framework of recommended Integrated Reservoir Management Practices with detailed and structured multi-disciplinary workflows. Information Technology plays a key role in all these workflows via automation, data integration and visualization. Second is a new generation data integration and analysis tool facilitating data and work flow integration and providing a common platform for intelligent and interactive display, thus promoting collaboration to achieve synergistic benefits. Third is the application of advanced simulation-based streamline techniques whereby new technology and workflows are deployed, with full collaboration among stakeholders.The Integrated Reservoir Management Practices include a set of highly interactive workflows set in a continuous improvement loop: Data Gathering Requirements, Data QC/QA, Data Analysis, Integration and Visualization, Opportunity Generation, Execution and Monitoring. ZADCO is following these workflows with significant improvement in work efficiency and results. In the collaborative environment, open communication and sharing of knowledge is strongly encouraged among stakeholders to assess the problem from different perspectives. This often results in creative solutions being developed. The new generation integration tool further facilitates collaboration as it retrieves data from reservoir static and dynamic models, surveillance data such as cased-hole logs and pressure data, and displays them for interactive work sessions, including animated display to give extra insight on time dependent data. The streamlines enable model-based well allocation factors (WAFs) to be calculated to supplement analytically derived WAFs, guiding injection optimization and thus resulting in improved reservoir management.These advanced workflows and tools have helped ZADCO to make timely and informed decisions, resulting in significant savings to the company, and at the same time improving understanding of reservoir behavior and facilitating optimization of ongoing development plans. The advanced workflows and tools have been recognized by Shareholders as game changers greatly needed to better manage the complex giant carbonate reservoir.
Integration of the dynamic data and geologic data led to a significant enhancement in understanding the reservoir flow behavior of a major limestone reservoir in the Arabian Gulf. High-permeability streaks were found to be the main factor controlling the reservoir performance and water breakthrough in the northern sector of the field. The methodology presented in this paper integrates static and dynamic data in such a way to ensure consistency between the data and enable better understanding of the reservoir flow characteristics. The study accommodates all available data from core, well test, O.H. logs, PLT, PNC logs and production data. Core data was used to identify the permeability variations vertically and horizontally. In order to extend the knowledge and map the area where the high-perm streaks exist, well test, production logs, TDT/PDK logs, production and injection data were used to link the reservoir heterogeneity on well-well and on a field scale basis. Statistical wire line log analysis was conducted and found that the Rxo log response was quite useful for reservoir characterization in this regard.The results of the analysis showed good consistency with what was concluded from dynamic data. The core and dynamic data indicate the high-permeability streaks cannot be correlated all over the reservoir, they are strictly present in the northern sector. There is a clear borderline splitting the reservoir into two sectors, the high permeability northern sector, and the low permeability southern sector. The profiles measured with the production logs (WFL & TDT/PDK) consistently indicated the presence preferential behavior that interpreted as a highñpermeability streaks at the top part of the reservoir. A linear increasing WOR trend of the wet producers is a clear indication of presence of permeability contrast that interpreted as a presence of hi-permeability streaks. The dual-permeability/porosity behavior as interpreted analytically utilizing pressure transient data found to be the response of the presence of hi-permeability streaks. This paper shows how data integration improved our understanding of reservoir performance and reduced the production uncertainty of this heterogeneous limestone reservoir. The modified 3D simulation model matched, for the first time, the reservoir water cut performance. Background The limestone reservoir of concern is a shallow dipping anticline located offshore in the Arabian Gulf, UAE. The average reservoir thickness is 68 ft., average porosity is 24%, and permeability ranges from 3 md to 96 md. The field is currently developed with a Staggered Line Drive waterflooding scheme. The scheme divided the field into twenty five-spot patterns of unequal sides with four producing lines, and three injection lines. In addition there is a ring of peripheral injection wells (Figure1). Fig. (1) Well location map
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