Al-Kandary, Ahmad (Kuwait Oil Company) | Al-Fares, Abdulaziz (Kuwait Oil Company) | Mulyono, Rinaldi (Kuwait Oil Company) | Ammar, Nada Mohammed (Kuwait Oil Company) | Al naeimi, Reem (Baker Hughes) | Hussain, Riyasat (Kuwait Oil Company) | Perumalla, Satya (Baker Hughes)
Role of geomechanics is becoming increasingly important with maturing of conventional reservoirs due to its implications in drilling, completion and production issues. Exploration and development of unconventional reservoirs involve maximizing the reservoir contact and hydraulic fracturing both of which are heavily dependent on geomechanical architecture of the reservoirs and thus require application of geomechanical concepts from the very beginning.
To support the unconventional exploration and conventional reservoir development in Kuwait, country-wide in-situ stress mapping exercise has been carried out in nine fields of Northern Kuwait. Stringent customized quality control measures were put in place to evaluate stress orientation. Cretaceous and sub-Gotnia Salt Jurassic rocks exhibit distinct patterns of stress orientations and magnitudes. While the variations in stress orientation in the Cretaceous rocks are within a small range (N40°E-N50°E) and consistent across major fault systems, the Jurassic formations exhibit high variability (N20°E-N90°E) with anomalous patterns across faults as well as in the vicinity of fracture corridors. Moreover, the overall stress magnitudes were found to be much higher in the strong Jurassic section compared with the relatively less strong Cretaceous strata. During the analysis, it was also observed that several natural fractures in Jurassic reservoirs appear to be critically stressed with evidences of rotation of breakouts.
Using geomechanical models from a specific field, the effects of in-situ stress, pore pressure and rock properties on formations were evaluated in inducing wellbore instability during drilling operations in a tight gas reservoir. It was found that the most favorable orientation for directional drilling is parallel to the maximum horizontal stress (SHmax) within that field.
The geomechanical study provided inputs not only for wellbore stability during drilling, but also regarding the response of natural fractures to in-situ stresses to become hydraulically conductive (permeable) to act as flow conduits. The fracture model of the field shows that the dominant fracture corridor trend in the field is NNE coinciding with present day in-situ maximum principal stress direction.
GIS-based software has been developed under the PIRAM (Pipeline Ice RiskAssessment and Mitigation) program for performing pipeline routing and burialanalysis for protection against ice keel gouging. Results are presented for ahypothetical pipeline in the Canadian Beaufort Sea. A probabilistic pipelineburial analysis is incorporated that accounts for the influence of sub-gougesoil displacements. Ice gouge rates and geometry are based on repetitivemapping survey data.
This paper presents the workflow and the results of integration of seismic, well and production data on Habban Field to optimize well locations.
Habban Field is located in the Jurassic Marib-Al Jawf-Shabwah basin of Yemen (Block S2). Development targets in Habban Field are fractured Precambrian Basement, Kohlan and Shuqra formations (Middle Jurassic).
Main challenges faced in the Field are Basement heterogeneity, fracture distribution and their connectivity, lateral variation of Kohlan Formation and the overlying salt diapirs/walls hampering the seismic imaging. The difference between a good and a dry well is whether it is encountering main fracture corridors or not. Fracture corridors (along the faults) have limited lateral extent and due to overlying salt diapirs well trajectory optimization is very challenging. Reflection pattern in the Basement is quite chaotic. Therefore, it was important to come up with a workflow to image faults within the Basement so that highly deviated to horizontal wells can be drilled to enhance production and optimize recovery.
In order to address these challenges, wide azimuth 3D seismic was acquired and processed in different azimuths. The study has been conducted using 3D seismic dataset and derived seismic attributes combined with information from thirty one wells including image and production log interpretation. The workflow highlighted the value of G&G integration to better outline uncertainty and to mitigate risks during well locations and trajectory planning. In this contest structural attributes (i.e. Ant-Tracking) have been crucial in order to define and identify the faults zones for optimizing horizontal wells targeting multiple fracture zones.
On the other hand integration of G&G and production data highlights the limitation in defining a one-to-one correlation between seismic, well and production information mainly due to reservoir complexity and scale resolution.
An azimuthal seismic study for fault and fracture identification was carried out on a giant onshore carbonate oil reservoir in the U.A.E., Middle East. The seismic reflectivity analysis was performed using advanced independently processed azimuthal sectors from compressional waves. The seismic attributes demonstrated superior capability of defining accurately the detailed reservoir faults and the fracture networks. Although the full azimuthal study achieved excellent results, the azimuthal stacks were observed to sharpen the reservoir subtle structural features. Beside the traditional land seismic data processing, additional challenges were to properly process the seismic data due to the surface topography and the lateral variations in subsurface rock properties. Azimuthal processing successfully demonstrated:
a) Improved fault imaging relative to the available conventionally processed seismic data.
b) Additional information about the seismic anisotropy in the reservoir zones.
The analysis showed encouraging results and a relatively good match to known fault/fracture locations. The successful results of the study suggest that high quality 3D wide azimuthal seismic data with relative true amplitude preservation can be used to identify the fracture permeability pathways in carbonate reservoirs. The azimuthal sectors study and results facilitated the quantification of the presence of faults, and suggest that fractured zones can be identified. Another important procedure in this study is the use of the integrated approach during processing and interpretation. Overall, the results of this Azimuthal Study for fractured carbonate reservoir characterization revealed encouraging outputs and valuable guidelines for similar studies in the future.
Hassi Messaoud in Algeria has been a major oil-producing field for more than 50 years, with many hundreds of wells successfully drilled. The complex geological structure and varying amounts of depletion mean that 3D geomechanical modeling techniques bring great benefit, particularly in predicting well-bore stability, sanding potential, and hydraulic fracturing. This paper describes such a model for one sector of the reservoir, creating 3D maps of mechanical properties and a 3D stress state that can be updated over time as pore pressures change. Several new methods of applying the results to well design are presented, including the creation of "mud weight cubes?? and "sanding potential cubes?? to assist with trajectory optimization and mud weight selection, and to provide limits on safe drawdown.
The Lower and Middle Ordovician paleocave systems form an important type of reservoirs in the Tarim basin, China. To better understand the impact of fractures on the paleocave reservoir development, with acquired wide azimuth 3D seismic data, both post-stack volumetric geometric attributes and P-wave azimuthal AVO analysis are applied to characterize multi-scale fracture distributions. In this study, volumetric seismic attributes including dip, discontinuity and curvature are used to identify sub-seismic faults and associated fracture corridors and to describe subtle folds and flexures within the reservoirs. P-wave azimuthal AVO analysis is applied to detecting high angle fractures. Six azimuth-sectored stacks are used to compute P-wave seismic anisotropy from which fracture density and orientation are estimated.
Two major sets of conductive fractures trending northeast and northwest, associated with different tectonic events, are identified using imaging logs from seven wells in the study area. Fractures predicted from geometric attributes and from the P-wave azimuthal AVO analysis are compared. The feasibility of two approaches for characterizing and mapping various types of fractures is investigated. Our results show that geometric attributes can better allow detecting and imaging sub-seismic faults and fracture corridors. The azimuthal AVO analysis allows detecting zones associated with both large scale fracture corridors and small scale diffuse fractures. However, the poor quality data and local geological structures may prevent from using obtained fracture predictions in a quantitative way. Integrating geometric attributes and azimuthal AVO analysis allows obtaining a comprehensive fracture distribution from fracture networks on the corridor scale to diffuse fracture distributions on the small scale. In this paper, case studies are used to illustrate how these two approaches can be integrated to provide a comprehensive multi-scale fracture distributions calibrated with well data and validated against the conceptual fracture models.
Some of the most active and high profile hydrocarbon plays currently being explored and developed around the world lie below a salt canopy. Drilling through a thick salt canopy has the potential to provide a faster route to reach a sub-salt objective rather than drilling through the overpressured sedimentary section in a supra-salt mini-basin. Unfortunately, numerous geological factors can complicate the drilling leading to expensive sidetracking or casing operations. Wellbore stability problems, such as unexpected low fracture gradient, are relatively common while drilling close and out of salt structures. Significant savings on drilling costs can be made if potential wellbore stability problems could be identified and avoided in the well planning process. In this paper we present a workflow to improve wellbore stability predictions for drilling through and near salt structures.
Common assumptions in wellbore stability studies on stress magnitude and orientation are not valid while drilling close to a salt body as salt structures create, due to their shape and rheological behavior, a perturbation of the stress field with strong spatial variation of the principal stress magnitudes and orientations. To provide realistic stress input data for wellbore stability predictions, the stress fields around salt structures are simulated using non-linear materials and realistic 3D geometries. The workflow presented in this paper provides an efficient way to create realistic 3D finite-element based geomechanical simulations from these complicated structural data.
The workflow allows for a detailed simulation of the stress field around salt bodies that is new to the hydrocarbon industry and helps to significantly reduce the risk for wellbore failures of increasingly costly wells drilled to exploit, e.g., sub-salt plays in the Gulf of Mexico and offshore Brazil.
Gangopadhyay, Abhijit (BP America) | Johnston, Rodney (BP America) | Lucas, Jennifer (BP America) | Ramirez, Jaime (BP America) | Gillham, Travis (BP America) | Peña, Victor (BP America) | Wirnkar, Fabian (BP America)