Meziani, Said (ADNOC E&P) | Ibrahem, Mohamed Sayed (Abu Dhabi Marine Operating Co.) | Al-Hossani, Khalil (ADMA-OPCO) | Matarid, Tarek Mohamed (Abu Dhabi Marine Operating Co.) | Al Badi, Bader Saif (ADNOC)
A green field offshore Abu Dhabi is planned to be developed with miscible crestal gas injection and peripheral water injection scheme. Close to 100 slanted and horizontal wells (single in dual/triple Reservoirs) will be drilled from 2 artificial islands targeting four Upper Jurassic carbonate Reservoirs. Risks appear in developing the field due to the uncertainties related to complex faults and fractures network, carbonate reservoirs heterogeneity, Tar Mat, sour fluid production, and high departure wells.
This paper illustrates full field development plan optimization studies that were conducted on a green field. The main objective of those studies was managing the reservoir uncertainties to enhance the full field development plans. 3D seismic, detailed sedimentological study, identified Reservoir rock types, Reservoir fluid characterization (Equations of state) and special core analysis (SCAL) using data collected from limited available wells were comprehensively evaluated and integrated to the input data of a 3D dynamic reservoir model.
In order to achieve the studies objectives, number of parameters were addressed and optimized during assess and select phases of the full field development plan. These parameters are miscible and/or immiscible Gas injection scheme, peripheral Water Injection, Gas Injection timing and balance (standalone field development), and well locations based on structural and sedimentological uncertainties.
Integration of static and dynamic data supported the development plan optimization to address the high uncertainty of the targeted Reservoirs. In addition, several sensitivity studies have been conducted for the reservoir uncertainty parameter ranges to understand their impact on the full field development plan.
The post stack seismic fracture prediction method consistently shows fractures that are similar to those indicated by well methods and therefore seismic can be used to detect natural fractures between wells. The confidence in the seismic fracture prediction method's ability to capture information about fracture in Carbonate reservoir has increased if the well data are accurately integrated.
This paper describes an approach in characterizing fractured reservoir of upper Jurassic Carbonate using seismic structure attribute maps. The ultimate objective of this study was to attempt to map permeability scalar inter-well for the contribution to the simulation model and the subsequent development plan of an oil field offshore Abu Dhabi.
The studied field is not developed, but the subject reservoir was sparsely sampled with logs, limited well tests, limited cores, one FMI and one full waveform sonic. We have studied and analyzed the well based fracture detection results. The well analysis included FMI study, Stoneley waveform, well production tests and core images. The likely fractured layers were identified at the lower dense part of the reservoir. Well seismic synthetics were generated and the fractured layers were found to exist in less than one cycle.
Following the fractured layers identification in the seismic cube, an intensive seismic attribute analysis was conducted. The studied seismic reservoir attributes includes spectral decomposition analysis of Amplitude and Phase followed by structure attributes such as Coherency, Curvature, Amplitude change in X or Y and Azimuth. Here we report and analyze the fracture prediction results for Carbonate reservoir.
A consensus results from borehole ellipticity, Seabed ramp and near Seabed seismic structure map versus known regional stress will be presented as guide of current stress direction. Based on the extracted fracture map from seismic, the current stress direction and the well permeability scalar, a 1km x 1km permeability scalar map was generated.
Matarid, Tarek Mohamed (Abu Dhabi Marine Operating Co.) | Belaid, Kamal (Abu Dhabi Marine Operating Co.) | Ishiyama, Tomohide (Abu Dhabi Marine Operating Co.) | Lehmann, Christoph Thomas (Abu Dhabi Marine Operating Co.) | Al Riyami, Ahmed (ADMA-OPCO) | Seddik, Sameh (Abu Dhabi Marine Operating Co.) | Morrison, Dave (WesternGeco) | Al-Jarwan, Ali Rashid (ADMA-OPCO) | Strobbia, Claudio (WesternGeco)
In conventional seismic data processing Scholte and Guided Wave data are commonly considered as noise and therefore, are removed at an early stage of any seismic data processing sequence. This paper describes an innovative approach in characterizing near sea bed via surface wave inversion using Scholte wave data.
2-D & 3-D OBC seismic data sets were selected and reprocessed as a test focusing on shallow near surface data. The ultimate objective of this work was to attempt to locate the closest area to borrow the necessary volume of sediments / sand for the construction of artificial Islands (2) which are required for the development of an offshore oil field. In addition to the primary geotechnical objective, the test aimed to validate the potential of surface wave inversion using OBC data in shallow water.
The near surface characterization revealed a complex geology with velocity inversions and the results were incorporated to optimize the geothechnical survey program since it was able to differentiate a relatively low velocity anomaly area which could be related to soft sediments from hard rocky surface having a higher shear velocity.
Work Approach & Results
The work was carried out in three Phases in a collaborative approach between all involved parties. Phase-1 consisted of the extraction of the dispersion curves of the Scholte wave fundamental mode along one 2D OBC (Ocean Bottom Cable) seismic test line using both hydrophone and geophone shot records Figures-1 to 3.
These dispersion curves were inverted to Vs section and then a Vp section was produced as depicted on Figures-4 & 5 respectively.
The main observations made at the completion of this Phase-1 are:
Phase-2 consisted of the processing of an area of 120 km2 of 3D OBC seismic data (Figure-1) using the same approach applied in Phase-1. Vs cube was produced (Figure-6) and it is showing very encouraging results.
Acquisition footprint is a pattern on seismic data which is mainly caused by the sparseness of the acquisition geometry. It hinders seismic interpreters from accurate structure analysis by masking geological significances such as fault lineaments, channels and karsts. It is triggered by coherent changes in case of variable acquisition parameters and/or methods in the field, or alignments caused by the direction of data acquisition, and it is predominant on sparse acquisition geometries. Furthermore, it might be accentuated by multi-channels seismic processing such as stacking, DMO and pre-stack time migration if the aliased noise produced by the sparse geometry does creep into the seismic data.
In general, the acquisition footprint signature is rather strong in the shallow events due to relatively lower fold. Hence, it is strongly dependent on trace mute designs and sensitive to the amount of moveout and NMO stretch, where the influence is progressively healed with depth due to higher fold, wider mute parameters and smaller NMO shift.
It is known that remnant acquisition footprints often exist on the data after the application of the 3D F-Kx-Ky wave number notch filter. Although it may not always appear on the vertical cross-sections and time slices prominently after the attenuation, it might be pronounced on edge detection attributes, such as coherency cube, curvature and/or seismic impedance. There is some ongoing debate in Abu Dhabi between processing geophysicists and interpretation geophysicists as to whether apply harsh filter to clean up the residual footprint or to be more conservative while preserving some desirable subtle geological features as possible.
This paper advocates the necessity of time-variant 3D notch filtering approach regardless of the acquisition geometry and/or the area by showing some case histories from 3D seismic surveys offshore and onshore Abu Dhabi with three different acquisition geometries; orthogonal OBC patch layout, orthogonal land layout, and parallel OBC patch layout. Change of footprint characteristics in time, in association with adaptiveness of various notch filters in temporal/spatial domain, will be discussed and demonstrated for each geometry type.
Ibrahim, Khalil (Abu Dhabi Marine Operating Co.) | Walia, Samir Kumar (Roxar ltd) | Matarid, Tarek Mohamed (Abu Dhabi Marine Operating Co.) | Al-Harbi, Haifa (Abu Dhabi Marine Operating Co.) | Afia, Mohamed Sayed (ADMA-OPCO) | Shaalan, Mohamed Essam (Roxar AS)
Defining the range of uncertainty is a crucial part in the oil field development particularly for carbonate reservoirs that have limited well data and with the absence of dynamic data. It is very important to develop an in-depth understanding of the range of uncertainty of all reservoirs parameters such as:
- Structure uncertainty
- Lithofacies and reservoir rock types
- Static reservoir attributes population technique (Porosity, Permeability, & Water Saturation)
Although outcrops and analogs are often employed to define reservoirs model parameters, it is still challenging to define and agree on the relationship between modeling parameters and their distribution ranges.
This paper addresses the impact of uncertainty of different modeling parameters on the volumetric calculations and full field development scenarios starting with structure model. Various areal and vertical uncertainties were investigated to set the structure uncertainty ranges. Then, the identified depositional environment models were used as guides to set the uncertainty ranges for each lithofacies association. The reservoir rock types were directly affected by both structure and lithofacies association models. Different ranges of variations were used for each rock type within each reservoir layer to ensure capturing the lateral and vertical reservoir heterogeneity and to propose multi distribution scenarios for each reservoir tock type within non-cored intervals/areas.
The petrophysical parameters were conditioned to the reservoir rock types model. So, they were directly affected by multi scenarios of RRT models.
In conclusion, 20 volumetric estimates were calculated and evaluated to define the probabilistic scenarios P10, P50, and P90 that will be used to investigate the full field development scenarios.
Understanding field uncertainty is crucial challenge affecting the decision making at the early stage of development of green fields. Challenges increase with limitation of core, log, and dynamic data as well as poor wells distribution overall the field.
This paper illustrates a case study of quantifying and evaluating the reservoir/field uncertainties using the advanced uncertainty tools and options of IRAP/RMS 3D modelling software. The workflow included structure modelling, facies distribution, porosity/permeability distribution, water saturation modelling and volumetric estimations.