The reservoir in discussion is a tight carbonate reservoir with low productivity and relatively under-developed albeit the huge in-place volumes. The expectation is that a detail reservoir characterization will provide insight on factors affecting reservoir productivity, spatial distribution of productive portion of the reservoir and offering solution to overcome reservoir tightness.
The case study discusses on how a comprehensive multi-discipline review unravels and presents a robust reservoir heterogeneity framework. A geological review that includes both depositional and diagenetic process is performed to understand distinct components/factors responsible for reservoir heterogeneity. Simultaneously, petrophysical assessment was performed to quantitatively define rock grouping based on porosity-permeability, capillary pressure and pore throat distribution in the log and core domain.
The multi-discipline observations were then reconciled to establish relationship between the process origin and the resultant product of specific group/range of reservoir petrophysical properties. The multitude of pore throat characters and its petrophysical properties were linked to the underlying geological processes. The established heterogeneity framework provides clarity on spatial distribution of the reservoir sweet-spot, factors controlling low productivity and the required mitigation.
The study provides a complete journey of unlocking tight reservoir potential. It illustrates the geological studies influence toward innovative completion technology selection, design, and execution to overcome reservoir challenge. The study is supported by recent drilling and test results, hence offering insight for adoption and lesson learned.
The carbonate reservoir properties distribution can be completely different from what expected of the depositional framework. The subsequent diagenesis processes, often multi stages, commonly overprint the primary porosity-permeability system. Therefore, comprehensive understanding of both depositional and diagenesis processes is very crucial to produce robust reservoir model.
In the case of mature field development with abundant data availability, reservoir modeling should be more data driven and integrate multi-discipline observation and understanding. The objective is to yield less-subjective and data-consistent model with better prediction quality. However, the understanding of geological processes governing reservoir heterogeneity shall be made as foundation in all cases.
The case study discusses on how a comprehensive multi-discipline review unravels and presents a completely new reservoir heterogeneity framework. Diagenesis processes were investigated from both burial and tectonic evolution/ tectonostratigraphy perspective. The 3D reservoir rock type framework as net product of deposition and diagenesis process is created by combining well vertical heterogeneity and seismic lateral information into 3D trend model.
The integrated and data-driven modeling approach reconciles process origin and the resulted reservoir heterogeneity. The inclusion of tectonostratigraphy component leads to better prediction result. Multi-disciplines integration provides an interpretation corridor, hence minimizing error due to subjectivity and/or limited level of experience.
The newly built reservoir model serves as basis for development plan optimization in the respective reservoir. The drilling result of some recently drilled wells shows a very good consistency with model prediction.
Gazar, Ashraf Lotfy El (Abu Dhabi Company for Onshore Petroleum Operations Ltd. ADCO) | Alklih, Mohamad Yousef (Abu Dhabi Company for Onshore Petroleum Operations Ltd. ADCO) | Al-Shabibi, Tariq Ali (Abu Dhabi Company for Onshore Petroleum Operations Ltd. ADCO) | Latief, Agus Izudin (Abu Dhabi Company for Onshore Petroleum Operations Ltd. ADCO) | Fauzi, Tengku Mohd (Abu Dhabi Company for Onshore Petroleum Operations Ltd. ADCO) | Syofyan, Syofvas (Abu Dhabi Company for Onshore Petroleum Operations Ltd. ADCO) | Hashimura, Tadashi (Abu Dhabi Company for Onshore Petroleum Operations Ltd. ADCO)
This work presents a case study of developing the transition zone for a giant oil reservoir with significant gas cap and water aquifer, in Abu Dhabi-UAE, addressing geological and dynamic aspects, field development approach and present status. The reservoir lies within a relatively low relief heterogeneous carbonate structural trap and characterized by lateral and vertical variations in reservoir rock and fluid properties. Given the relatively low permeability of the mentioned reservoir, the transition zone contains a significant STOIIP; which called for this challenging development.
A number of parameters were addressed and optimized as part of the transition zone development plan. The dynamic modeling suggests that a full field ultimate recovery of 70% can be achieved by developing the transition zone. However, considering the complexity of the reservoir, thickness of the transition zone and current market conditions, the field development would be economically viable for a period of 50 years under miscible hydrocarbon WAG, provided the most effective development strategy in terms of the definition of transition zone, optimization of the number, location, orientation and horizontal reach of the proposed wells. Various development strategies for the transition zone were investigated during the study considering all possible uncertainties and economic drivers, all of which are discussed in details in this paper.
12 years of early production scheme (EPS, 1993 to 2005) and 12 years of phase-I development helped better understand the reservoir and characterize the transition zone. Total of +150 wells penetrated the reservoir with good data gathering (ROS, Core, SCAL, PVT, MDTs…etc.). PVT studies indicate a wide range of compositional variation areal and vertical, which further complicates the development plan considering the surrounding sensitive environment.
The transition zone is defined by rock types and the corresponding critical saturation. The amount of recoverable oil in the transition zone is depending on the distribution of oil saturation as a function of depth and the relationship between initial and residual oil saturation in the transition zone.
The reservoir is under EOR (Miscible HC GI at crest and WAG at flank) since commissioning of phase-I in 2005 and tracers were injected in 2012; adding challenges to the history matching and tracking of the flood front. Given the limitation on surface handling capacity of the current facilities, the transition zone development called for well placement in the upper part of the transition zone using 6 months WAG cycles. The first well of the transition zone development has been drilled; which has positively validated the definition of the transition zone, built confidence on the subsurface modeling approach and commended the planning strategy.
Latief, Agus Izudin (Roxar (M) Sdn. Bhd.) | Ridzuan, Ahmad Idriszuldin (Petronas (Kuala Lumpur)) | Faehrmann, Paul A. (Shell) | Macdonald, Alister C. (Roxar Software Solutions) | Arina, Wardah (Petronas) | Rahman, Gozali (Roxar Software Solutions) | ab rahman, mohd elzrey
Baram is a giant mature field situated, offshore Sarawak Malaysia. Reservoirs consist of an approximately 7000 ft thick-stacked sequence of shallow marine sands, distributed in excess of 200 zones. The field is extensively faulted. Early Growth faulting followed by a later compressional phase has led to complex fault geometries. The field has been producing for over 40 years and presently has 175 wells.
Although the reservoirs are generally of good quality, the field currently has relatively low production rates, a low recovery factor, and a significant amount of remaining reserves. The geological complexity poses a key challenge, and a robust static reservoir model is a prerequisite for efficient reservoir management and for identifying viable Improved Oil Recovery (IOR) measures.
Static models of the Baram field had previously been constructed. This modelling took in excess two years to complete and the models were segmented into 10 pieces, as technology during this period was unable to tackle complex fault geometries. Due to the results of the static / dynamic modelling being insufficiently robust when tested during a drilling campaign in 2009, the decision was made to remodel.
The Baram subsurface team was challenged with building a static model which could be used for field management and IOR /EOR process selection and optimization within a six month timeframe. This is to allow for early investment decisions and an accelerated reversal of production decline. The key aspects of the fixed timeframe static model construction are described below. They consist of:
1. The subdivision of the field into independent models.
2. The utilization of a modern algorithm to model complex fault geometry.
3. Nested stratigraphic modeling.
4. Parallel property modeling and the re-combining of results into a single simulation grid to enable integrated reservoir
A full focus on the importance of the timeline and early investment, plus the adoption of a variety of strategic project
management measures and use of "state of the art" modeling technology can allow fit-for-purpose static models to be delivered on time.