Abdallah, Dalia (ADCO) | Al-Basry, Ali Hassan (Abu Dhabi Co. Onshore Oil Opn) | Zwolle, Simon (Abu Dhabi Co. Onshore Oil Opn.) | Grutters, Mark (Shell) | Huo, Zhongxin (Shell Global Solutions) | Stankiewicz, Artur (Schlumberger Tech Services)
Asphaltene is the heavy component of a crude oil that constitutes a potential problem because of its tendency to precipitate and deposit causing blockage in tubulars, pipelines and surface facilities leading to decline in oil production. There are a number of wells affected with asphaltene in an onshore field in Abu Dhabi and this is likely to increase in the future with the implementation of Artificial Lift (AL) and HC/CO2 gas injection for EOR.
Mitigation strategies in the field have been concentrating on design of remedial solvent treatments in combination with mechanical methods for removal of deposits. The company's approach has been shifting in dealing with asphaltenes from reactive to proactive by conducting studies to: understand asphaltene stability in the different fluids, model the behavior across the whole field, look at the effect of HC/CO2 gas injection on asphaltene stability and finally develop optimal preventative techniques to reduce treatment costs.
The study in this onshore field in Abu Dhabi was conducted on oils collected from different zones. The first part of the study involved analysis of different stock tank oil properties, e.g. API, Sulfur content, Nickel content, asphaltene content and viscosity to look for correlations that can help in identifying the problematic areas in the field. The second part of the study involved asphaltene stability screening tests, e.g. SARA screen, to determine whether the fluids from the different zones are stable or unstable with respect to asphaltene. Live-oil depressurization experiments were conducted on selected wells to determine the Asphaltene Onset Pressure (AOP) at different production conditions using solids detection system with Near Infra-Red (NIR) and High Pressure Microscopy (HPM) for visual confirmation of asphaltene particles. The data from the live-oil testing was then used to calibrate Shell's thermodynamic model which was then used to investigate the effect of changes in process conditions on asphaltene stability phase envelopes. Results of thermodynamic modeling can be applied on the full field which will aid in developing appropriate inhibition and remediation strategies to deal with the asphaltene challenges.
Lawrence, David A. (ADCO) | Al Ali, Malalla (Abu Dhabi Co. Onshore Oil Opn.) | Vahrenkamp, Volker C. (Abu Dhabi Co. Onshore Oil Opn.) | Al Shekaili, Fatema (Abu Dhabi Co. Onshore Oil Opn.) | Yin, Yahui (ADCO Producing Co. Inc.) | El Wazir, Zinhom Ali (Abu Dhabi Co. Onshore Oil Opn.) | Ribeiro, Maria Teresa (Partex Oil and Gas) | Mueller, Klaus W. (Abu Dhabi Co. Onshore Oil Opn) | Al-Madani, Noura Mohammed (ADCO Producing Co. Inc.)
A super-giant carbonate field in Abu Dhabi has most of its remaining reserves in carbonate build-up and prograding basinmargin deposits of Lower Cretaceous age (Shuaiba Formation). To guide further field production, a sequence stratigraphic framework was developed based on integration of core, log and seismic data. This framework is the cornerstone for building a new reservoir model and provides the key for a better understanding of facies and flow unit continuity guiding present and future field production and performance.
Approximately 730 wells, wireline logs and the latest core descriptions were integrated for this study. Another key element was the incorporation of 3D seismic data coupled with several iterations between well log and seismic picking. Detailed seismic interpretation led to the delineation of 3rd and 4th order sequences. The picking of higher order sequences was based on well data guided by the seismic surfaces. This study provides an excellent example of extracting maximum information from seismic and the full integration of geoscience and production data to provide a new 3D framework.
The sequence framework uses a consistent nomenclature based on the Arabian Plate Standard Sequence framework for the Aptian (van Buchem et. al., 2010). The Shuaiba is subdivided into six 3rd order sequences (Apt 1, 2, 3,4a, 4b, and 5) which, based on stacking patterns, record a complete 2nd order cycle of Transgressive, Highstand, and Late Highstand systems tracts (Apt 1-4b). The Bab Member (Apt 5) and Nahr Umr Shale form the Lowstand to Transgressive systems tracts of the next Super-sequence.
The third order Apt 1 sequence and the Apt 2 TST form the 2nd order transgressive systems tract, characterized by backstepping and creation of differential relief between the Shuaiba shelf and Bab intra-shelf basin. These sequences are dominated by Orbitolina and algal/microbial Lithocodium/Bacinella fossil associations.
The Apt 2 HST and Apt 3 Sequence form the 2nd order early highstand systems tract during which the platform area aggraded and the topographic split into platform, slope and basin became most pronounced. Sediments are extremely heterogeneous and varying properties introduce significant problems in understanding fluid flow. During the regressive part of the Apt 3 sequence accommodation space was limited and deposition switched to progradation at the platform margin. The platform top is characterized by thin cycles of rudist floatstones/rudstones separated by thin cemented flooding and exposure horizons, whilst
the platform margin received large quantities of rudstones, grain and packstones organized in clinoform sets. Clinoforms are separated by thin stylolitic cemented layers, which are transparent on seismic.
The Second Order late highstand systems tract is composed of 3rd order cycles Apt 4a and Apt 4b. These are detached from the main buildup, which probably stayed largely exposed, and form strongly prograding slope margin wedges composed of alternating dense mudstones (TST) and grainstone/packstone sequences with coarse grained top-sets which formed during highstand phases. Lowstand deposits of the Apt 5 cycle (Bab Member) are dominated by fine-grained siliciclastics capped by thin oolitic carbonate facies which are isolated from the main part of the field and are not hydrocarbon charged.
Clark, Andrew Brampton S. (Abu Dhabi Co. Onshore Oil Opn.) | Al Suwaidi, Mohammad Eid (Abu Dhabi Co. Onshore Oil Opn) | Elabed, Amjad (Abu Dhabi Co. Onshore Oil Opn.) | Mead, Jeremy David (Abu Dhabi Co. Onshore Oil Opn)
The well planning process in ADCO (Abu Dhabi Company for Onshore Oil Operations) is usually driven by subsurface disciplines as part of a full field development plan and consists of a limited number of development iterations related to surface (natural or man-made obstacle) or subsurface (anti-collision, dog leg severity) constraints. The apparent simplicity of this development description is hiding a much more complicated reality for many of the Abu Dhabi giant oilfields that have been producing for several decades. ADCO manages one such asset and is now developing previously untapped reservoirs within an existing mature field and is facing issues such as positioning new facilities; the necessary replacement and upgrade of old surface facilities; surface and subsurface congestion; continuous appraisal activities of additional hydrocarbon-bearing reservoirs; increased HSE compliance and competing land utilization requirements from third parties. Added to this is the diversity and complexity of the professional Information Technology software currently used by the surface and subsurface disciplines, most of which are legacy systems that are not integrated. As such, the business problem of planning and drilling several hundreds of new horizontal wells becomes more critical over time.
Several initiatives have been launched at Company level in order to address these issues such as streamlining the well placement process by using a new workflow Well Approval Process; a common corporate Geographic Information System (GIS) interface, as well as the planned integration with a Drilling Real Time Operations and Control centre (RTOC) for drilling follow-up activities.
While the current process always led to well placement in line with state-of-the-art practices, the on-going process improvements are expected to decrease the current stress level on surface and subsurface asset teams and ensure a manageable load level as drilling activity is scheduled to increase three-fold in the coming two years. This paper discusses the history of the field, its geological setting, the development of surface and subsurface assets and the challenges now being faced and how the challenges are being over come to ensure continue its continued development.
Mueller, Klaus W. (Abu Dhabi Co. Onshore Oil Opn) | Soroka, William L. (ExxonMobil Oil Indonesia Inc.) | Al Nahhas, Mohamad Samir (Abu Dhabi Co. Onshore Oil Opn.) | Sinno, Rick (PGS) | Martinez, Ruben D. (PGS Seres) | Hussein, Waleed (PGS) | LeCocq, Paul (PGS) | Al Baloushi, Mariam Nasser (Abu Dhabi Co. Onshore Oil Opn.)
An azimuth dependant processing pilot study was carried out in a large Middle East Field to evaluate if this technology has the potential to successfully identify fracture permeability pathways. The field is heavily faulted and fractured with good well control and therefore is a good candidate to perform this study. The success criteria for the Azimuthal processing are:
• Improved fault imaging relative to the available conventional processed seismic volume;
• Obtain information about seismic anisotropy in the reservoir zones.
This anisotropy will be linked in a full evaluation to fault & fracture density and orientation. The anisotropy can be measured via differences in seismic travel times or amplitudes / seismic attributes measured in the different azimuth seismic cubes.
Azimuthal anisotropy from a 3D land seismic dataset acquired in the U.A.E. has been analyzed using wide azimuth processing. Two different processing methods and flows were tested to derive optimum processed volumes. In both methods raw CMP gathers, after convolution, residual statics, and inter-bed multiple elimination were used as input data for the azimuth stack processing sequence. The two methods are
• Azimuth Sectoring
• Common Cartesian Offset Bins (CCOB)
Both processing methods have their benefits, one big advantage of CCOB is that you can stack very fast different individual azimuths together and get a sharper image, which results in better interpretation.
Azimuth sectors both parallel and perpendicular to the three major fault system orientations, were imaged separately to produce the six final azimuth volumes. Comparisons between the different azimuth sectors were used to detect azimuthal differences in velocities and amplitudes that could be correlated with fault and fracture orientation and magnitude.
The interpretation and validation of the results suggest that value is maximized by integrating multiple attributes that include horizon mapping for time differences, amplitude extractions for reflectivity differences and result validations with available well calibration. The azimuth sector results have aided in the quantification of fault presence, magnitude of throw and suggests that fractured zones can be identified which may indicate higher permeability pathways within the reservoir.
Another important learning from this case study is to use an integrated approach during processing and interpretation and don't look only at one single part, e.g. velocity cube.
Overall the results of this carbonate Azimuthal Pilot for fault and fracture characterization has produced encouraging results and valuable lessons learned to aid future studies.
Carbon Dioxide (CO2) Enhanced Oil Recovery (EOR) process is most likely to become the preferred hydrocarbon recovery process in future in Abu Dhabi. The complexity and cost of implementing large scale EOR projects require the development of a detailed EOR strategy, clearly defined targeted objectives, a visionary work-plan (roadmap) and staged evaluation prior to full field commercial implementation. Abu Dhabi Company for Onshore Oil Operations (ADCO) is in the process of conducting the first Middle-East CO2-EOR pilot in an onshore complex carbonate reservoir.
This paper discusses the design and implementation of the first ADCO CO2-EOR Pilot Project which addresses key technical and business uncertainties and risks associated with CO2 injection in ADCO reservoirs in the future. The pilot was considered the best approach to evaluate feasibility of this EOR approach on a field scale in addition to other verifications through laboratory and simulation studies.
The project started with a company-wide screening study which attempted to identify both the most appropriate EOR option for ADCO reservoirs and the best reservoir candidates. Subsequently, an in-house simulation study was conducted to confirm the best identified candidate reservoir. The Roadmap defined studies required to fill the required data gaps. Advanced CO2-PVT, Asphaltene and SCAL studies were conducted to reduce the uncertainties related to CO2 injection. The pilot objectives and constrains were clearly defined at the early stage of the project. Challenges of obtaining the required CO2 volumes for injection were overcome.
A history matched compositional reservoir simulation model was used as an effective tool to design and optimize the pilot. Sufficient time and effort were expended in the pilot design and optimization in order to meet the implementation objectives in a timely manner. These include drilling of the wells, construction of the surface facilities, development and execution of the surveillance and monitoring plan and finally the operation of the pilot.
This paper outlines the design and implementation of the first ever Middle-East CO2-EOR pilot in an On-shore complex carbonate field in Abu Dhabi, UAE.
Abed, Abdulla Abdul-fattah (Abu Dhabi Co. Onshore Oil Opn.) | El Gohary, Mohamed (ADCO) | Abu Snaineh, Adel (Abu Dhabi Co. Onshore Oil Opn.) | Guettat, Morched (ADCO) | Ahmad, Mubashir (Abu Dhabi Co. Onshore Oil Opn) | Lozano, Jose (ADCO) | Al Reyami, Mazin (ADCO)
An Offshore Gas Field discovered in early 70' is a large anticlinal structure located in the shallow marine waters west of Abu Dhabi island. The area is considered by UNESCO as Biosphere reserve and is protected. Several development options have been studied to develop the gas reserves from existing Artificial Island with a minimum impact to the environment.
Geological and reservoir simulation compositional models have been prepared to optimize the development plan, identify the minimum number of wells, target rates in order to maximize the gas recovery and sustain the gas plateau rate as long as possible. Building these models was a challenge due to the lack of 3D seismic data and the limited production data from the appraisal well.
Due to the sensitivity of the area, the main challenges of the project implementation are the impact on the environment during drilling phase and the facilities construction and its operation.
The required refurbishment of the existing island and access channel to the island was a concern that was studied. Drilling of 10 to 12 closely clustered directional deviated gas wells from one existing artificial island in the centre of the field into a High Pressure and High Temperature, high H2S (14-24%) and deep reservoirs environment is also a big challenge. To effectively drain the entire reservoir from the island, the rigs should be capable to drill more than 25,000 ft extended reach deviated wells.
Reducing the impact on this sensitive environment was the major concern; hence an HSEA study has been carried out to develop the mitigation plans. The possibility of drilling using more than one rig simultaneously on the island to deliver gas on time has been studied to minimize the duration of the drilling operation and associated risks. Special completion materials for these extreme environments were also studied. Material selection for different well types/conditions has been carried out.