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Kumar Mishra, Anoop (ADNOC Offshore) | Anurag, Atul (ADNOC Offshore) | Al Balooshi, Mohammed (ADNOC Offshore) | Javid, Khalid (ADNOC Offshore) | Sinha, Rakesh (ADNOC Offshore) | Al-Hashmy, Ghassan (ADNOC Offshore) | Hosany, Khalil (ADNOC Offshore) | Mills, Carey (ADNOC Upstream) | Basioni, Mahmoud (ADNOC Upstream) | Al-Blooshi, Abdulla (ADNOC Upstream) | Aryani, Fatima (ADNOC Upstream) | Mandl, Johannes (ADNOC Upstream) | Dasgupta, Suvodip (Schlumberger) | Raina, Ishan (Schlumberger) | Ali, Humair (Schlumberger) | Uruzula Abdulrahim, Jaja (Schlumberger) | Al-Afeefi, Baraka (Schlumberger) | Hollaender, Florian (Schlumberger)
Abstract Recent appraisal drilling undertaken by ADNOC in offshore Abu Dhabi has focussed on evaluation of the Middle Jurassic to Permian Deep Gas reservoir sequences. These formations are characterised by low porosity and permeability and typically contain either dry gas or gas condensate fluids. These appraisal activities form part of a larger program leading to development of these resources. Principal uncertainties addressed by appraisal drilling include determining fluid characteristics, reservoir properties and ultimately well deliverability. This paper uses one such recently drilled (typical) appraisal well as an example of the workflow employed. Exploration drilling of the Middle Jurassic to Permian reservoirs in this field dates back to 1984 and utilised available logging tools and techniques of the time. The current appraisal drilling program built on the results of this work and utilizes the latest available technology and interpretation techniques to both quantify reservoir and fluid properties and minimise subsurface development uncertainties. Typical data acquisition programs includes: conventional coring, advanced mud log data acquisition, triple-combo wireline data, borehole image data, elemental spectroscopy, azimuthal dipole sonic data and formation pressure measurements/samples. The formation evaluation program involved careful analysis and integration of this data to decide at first on formation sampling points and then subsequently testing zones. This approach necessitated the involvement of multiple stakeholders (end-users as well as people performing the interpretation) and required close communication to facilitate rapid, informed, decision making at key stages of the project execution. These different types of data become available at differing times during the course of drilling a well with the earlier acquired data informing the decision-making process on subsequent data acquisition. The first data to come in were the "mud logs" which includes drilling parameters (such as Rate of Penetration) and gas chromatography. This data provides an initial indication of potential zones of interest, along with fluid type. Following acquisition of wireline data, a "quicklook" formation evaluation was integrated with earlier geological analysis to determine the formation pressure and fluid sampling points. Combined together, these results formed the basis of an integrated reservoir and saturating fluid interpretation leading to the selection of perforation intervals for well testing. Effective implementation of this work flow requires a collaborative approach combined with ongoing data integration. This process of consultation across multiple subsurface disciplines and stepwise evaluation guiding future data acquisition requires a certain degree of evaluation flexibility but ultimately results in better decisions. The philosophy of integrating multiple data sources and disciplines in a collaborative evaluation and decision-making work flow is an essential enabler for the exploitation of the Deep Gas resource in Abu Dhabi. In the example well, test results are in accord with the log interpretation work and provide a path forward towards field development and gas production.
Abstract The Wasia unconventional oil potential in west onshore Abu Dhabi is comprised of Mauddud, Shilaif and Tuwayil formations. The Mauddud potentiality is a result of the downward oil migration from the mature Shilaif Kitchen. The high maturity of Lower Shilaif creates a fracture network that facilitates the primary migration downward into the Mauddud formation. This resulted in filling the Mauddud formation below the Shilaif kitchen and possibly the surrounding areas. Mauddud oil accumulation in the basin was supported by the presence of high hydrocarbon shows while drilling and high hydrocarbon saturation in the interpreted logs. In the Shilaif source rock, there are three distinct intervals that have potential for shale oil exploration activities in Abu Dhabi. The Lower Shilaif has the highest maturity values and the highest recorded porosity with a very low permeability, while the Upper Shilaif potential represent the thickest part and is expected to have higher permeability values as a result of the presence of lower argillaceous content. The Upper Tuwayil is comprised of shale sediments that are intercalated with Sandstone streaks. The Sandstone was developed as isolated but laterally extensive sand bodies that are separated by the shale layers. Tuwayil sandstone may represent an unconventional tight oil potential similar to that found in many other basins.
Abstract Objectives/Scope Late Cretaceous plate collision and subsequent ophiolite emplacement at the eastern margin of the Arabian Plate led to compressional events, responsible for the formation of the structural traps of the giant fields onshore Abu Dhabi. In addition, the onset of this structuration during the Turonian caused the configuration of some hence-to-forth overlooked features (pinch-outs and siliciclastic sand deposits). The objective of the present work is to analyze the origin and distribution of these geometries and their potential to constitute stratigraphic traps. Methods, Procedures, Process To understand the genesis and the distribution of these geometries which formed during the Late Cretaceous, we used a combination of large scale regional stratigraphic well correlations and seismic lines interpretation, together with age dating, core description, and well data information. The methodology consisted in using this data for detailed mapping of relevant time stratigraphic intervals, placing the mapped architecture in the context of the global eustatic sea levels and major geodynamic events of the Arabian Plate. Results, Observations, Conclusions The ensuing plate collision during the Turonian in eastern plate margin was felt hundreds of kilometers into the plate over Abu Dhabi area. Buckling and uplifting created paleo-relief which caused exposure and erosion of Wasia Group sediments in northern and eastern areas of Abu Dhabi Emirate. This led to the configuration of some overlooked stratigraphic features: eroded rims and lateral facies change against structural dip (Mishrif Formation); onlap pinch-outs onto flanks of major structures (Ruwaydhah Formations) and the deposition of siliciclastic sand deposits of the Tuwayil Formation. The features follow low relief areas along contemporaneous synclines in onshore Abu Dhabi and salt withdrawal synclines in offshore Abu Dhabi. With further advance of the obducting ophiolites, a foredeep developed leading to drowning of the previously exposed structures. Shales and interbedded limestones of the Laffan Formation were unconformably deposited over the eroded Wasia Group during the Coniacian transgression associated with the generation of this foredeep. They are now forming an extensive regional seal for these deposits forming potentially stratigraphic traps. We postulate that the rejuvenation of the Shilaif intrashelf basin during the Late Turonian and the deposition of the (Ruwaydhah Formation) was aborted at its early stages by periods of uplift, erosion and their successive erosional unconformities, features that are confirmed on the crest of several eastern area structures. This provided the context for the generation of pinch-out geometries that constitute potential stratigraphic traps downdip of major structures in Abu Dhabi. Novel/Additive Information Very little has been published about the outline and architecture of these stratigraphic traps in Abu Dhabi and the detailed circumstances that led to their genesis, topics that are comprehensively analyzed in the present work.
Abstract Rock typing is a key factor in reservoir characterization studies. It is often assumed that Static Reservoir Rock Types (SRRTs) are capable of assigning multi-phase flow characteristics, such as capillary pressure and relative permeability curves to the cells of dynamic simulation models. However, SRRTs fail to capture the actual reservoir variability, due to lack of representation of wettability difference at different elevations above Free Water Level (FWL), especially in highly heterogeneous thick carbonate reservoirs. These shortcomings of SRRTs can be resolved through Dynamic Reservoir Rock Types (DRRTs), in which wettability effect is imposed on SRRTs to generate saturation functions for simulation models. This research proposes a modified DRRT approach by integrating the data from geological models and SCAL tests. First, the defined static rock types are sub-divided into sub-static rock types using either porosity or permeability frequency distribution. Second, a modified correlation equation is proposed and applied to more accurately estimate the initial water saturation versus height above FWL from well logs. Third, each sub-static rock type is further divided into a number of DRRTs by determining the capillary pressure and relative permeability curves in the oil zone from the Gas-Oil Contact (GOC) to the Dry-Oil Limit (DOL). The DRRTs are extended to the zone from DOL to the FWL by including wettability effect which would affect the curvature of the relative permeability curves but not its saturation end points, through changing the Corey exponents in the modified Brooks-Corey model. This modified DRRT approach is applied in terms of the dynamic rock typing plug-ins to generate sub-rock types from static rock types, and build a comprehensive and automatic approach to generate saturation tables for dynamic rock types that can be prospectively loaded into commercial simulators for reliable reservoir initialization, history match and prediction processes.
Lv, Mingsheng (Al Yasat Petroleum Operations Company Ltd) | Al Suwaidi, Saeed K. (Al Yasat Petroleum Operations Company Ltd) | Ji, Yingzhang (Al Yasat Petroleum Operations Company Ltd) | Swain, Ashis Shashanka (Al Yasat Petroleum Operations Company Ltd) | Al Shehhi, Maryam (Al Yasat Petroleum Operations Company Ltd) | Luo, Beiwei (Al Yasat Petroleum Operations Company Ltd) | Mao, Demin (Al Yasat Petroleum Operations Company Ltd) | Jia, Minqiang (Al Yasat Petroleum Operations Company Ltd) | Zi, Douhong (Al Yasat Petroleum Operations Company Ltd) | Zhu, Jin (Al Yasat Petroleum Operations Company Ltd) | Ji, Yu (Al Yasat Petroleum Operations Company Ltd)
Abstract Western Abu Dhabi locates in the west of Rub Al Khali Basin, which is an intra-shelf basin during the Late Cretaceous. The Shilaif source, Mishrif reservoir and Tuwayil seal forms one of the Upper Cretaceous important petroleum systems in the western Abu Dhabi Onshore. However, less commercial discoveries have been achieved within Mishrif Formation during the past 60 years since the large scale structures were not developed in western Abu Dhabi and the stratigraphic traps have not been attracted attention. This study aims to investigate the exploration potential of both Mishrif structural and stratigraphic traps. It provided detailed study on Shilaif source rock, Mishrif shoal/reef reservoir and Tuwayil seal capability. Oil-source rock correlation, reservoir predication and basin modeling have been carried out for building Mishrif hydrocarbon accumulation model by integration of samplings, wire loggings and 2D&3D seismic data. Shilaif Formation is composed of laminated, organic-rich, bioclastic and argillaceous lime-mudstones and its generated hydrocarbon migrated trending to high structures. Three progradational reefs/shoals in Mishrif Formation were deposited along the platform margin, which are characterized by high porosity and permeability. Tuwayil Formation consists of 10-15ft shale interbedding with tight sandstone, acting as the cap rock of Mishrif reservoirs. Mishrif hydrocarbon accumulation mechanism has been summarized as a model of structural background controls on hydrocarbon migration trend and shoal/reef controls on hydrocarbon accumulation. It is consequently concluded that Mishrif reefs/shoals overlapping with structural background are the favorable exploration prospects, and oil charging is controlled by heterogeneity inside a reef/shoal, the higher porosity and permeability, the higher oil saturation. Two wells have been proposed based on the hydrocarbon accumulation model, and discovered a stratigraphic reservoir with high testing production. This discovery encourages a new idea for stratigraphic traps exploration, as well as implicates the great exploration potential in western Abu Dhabi.