Advancements in numerical well testing packages in interpreting pressure transient behavior of complex well geometries and reservoir structures have lead to an improved understanding of the multi-scale heterogeneity encountered in dual-porosity dual-permeability (DPDP) reservoirs. This paper demonstrates the power of numerical well testing models in handling conceptual cases of increasing complexity in dualporosity dual-permeability (DPDP) reservoirs where a high permeability matrix system interact with superk intervals, fractures, and faults systems with different levels of complexity. Numerical well test models are built using data from multiple scales and sources (image logs, flowmeter responses (PLTs), petrophysical logs (FALs), and seismic attributes) to match pressure transient responses of wells completed in dual-porosity dual-permeability reservoirs. Six generalized conceptual cases are presented in this paper; a vertical power water injector that initiated induced fractures due to injection above fracture pressure, a vertical well near an area of intersecting faults, a 40-degree deviated well intersecting diffuse fracture network, a deviated well near a conductive fracture corridor, a horizontal well intersecting a finite conductivity fracture, and a horizontal well intersecting an infinite conductivity fracture. An integrated approach was used to match the pressure responses in all cases. Experience shows that the most representative well test solution comes from a thorough integration of well-test data with all available static and dynamic data (e.g.
A solid understanding of challenging reservoir complexities such as, naturally fractured "super-k" zones, layered systems, or, wellbore conditions such as, thermally induced mobility changes in the near wellbore region due to injection and uneven formation damage distribution across the wellbore, is essential for a successful development of carbonate reservoirs. These type of complexities play a major role for both reservoir fluid flow and well productivity. An efficient and holistic approach encompassing multiple data sources like image logs, production analysis logs, and pressure transient analysis (PTA) outcomes is of paramount importance in the characterization process of carbonate systems. In this paper illustrative examples showing different complexities, at reservoir level and also at well level, are presented in a systematic way to show the importance of pressure transient analysis (PTA) insights as a building block in the description process of these challenging reservoir features. Reconciling the differences between the static and dynamic data sources in each case was a crucial step to minimize the uncertainties encountered and to significantly broaden the dynamic understanding of these complex reservoir heterogeneities under a synergistic approach. Pressure buildups and falloffs data from multi-well groups, were incorporated and analyzed by advanced numerical models. The selected interpretation models were dependent on the reservoir and wellbore condition diagnosed from the pressure derivative plots.
The objective of this work is to characterize the porosity distribution and the types of carbonate facies in the Mishrif Formation in the West Qurna/1 Oil Field using seismic inversion results, well log data and rock physics modeling. Identification of the pore system and the spatial distribution of lithofacies are keys for constructing Mishrif reservoir model, which have a great impact on the development of the most prolific reservoir in the field (Mishrif zone).
Seismic inversion involves the interpretation of elastic properties for facies based on the seismic response. It enables the modelling of lithology and porosity distribution in 3D space away from well control. In order to achieve the aim of the work, a step wise approach will be taken. First of all, deterministic seismic inversion was applied across the high resolution of 3D-seismic survey data over the West Qurna/1 Field. Then, the vertical distribution of porosity and facies recognition based on well log data and its relationship with elastic properties, integrated with seismic inversion results for validating at Mishrif intervals.
Deterministic seismic inversion was undertaken on the post-stack seismic dataset. The interpretation of seismically derived characterization in Mishrif reservoir indicated a different lateral distribution of acoustic impedance and three regions of channel (north, southwest and east). It can be seen a high acoustic impedance anomaly outside the channel in the western field sector which is heavily mud supported by peritidal carbonates (low quality facies of the reservoir). Whereas, carbonate tidal channel displayed a low acoustic impedance which reflect high porosity and good reservoir quality (grainstone channel or sholas). Furthermore, the interpretation of the well log and rock physic model was correlated with seismic inversion volume in terms of the lithology and porosity. Consequently, some zones which included carbonate tidal channel, displays a wide range of porosity and lithology fluctuations due to the impact of depositional environment (subaerial exposure).
The workflow provided insight into the distribution of petro-physical properties and quantification of their influence on dynamic reservoir behavior. The results also indicated the areas of high permeability and its component that may include fractures or connected vug systems. Water flood design and completion strategies (well trajectories) will be developed and succeeded according to the heterogeneous geological regions. Overall, this will ultimately lead to improve the development plan of wells in terms of production performance, recoverable reserves and economic value.
Beyond offshore West Africa where modern densely-sampled data from ships and satellites have played a key role in current understanding of passive margin evolution, Africa is in general rather unevenly known, especially in the subsurface in more remote areas. The GIS-based Exploration Fabric of Africa (EFA, the ‘Purdy project’) was designed to address that problem. It includes structural features such as faults and basin outlines but at a very high and often generalized level, divorced from their underlying genetic linkages. We have undertaken to compile a more detailed tectonic synthesis aimed to integrate understanding of the oceanic margins with the continental realm. This is an overlay to EFA with a variety of public domain, published, non-exclusive, and derivatives of proprietary work at a closer and more detailed level, importantly guided by known patterns of structural styles. Potential field (gravity and magnetic) data provide guidance in locating, extending, and connecting key mapped features; we then rely on the kinematic patterns to predict missing details in a testable interpretation. The result is a detailed structural features map that can function as a framework within which to target and prioritize both conventional and unconventional activity by operators and licensing/regulatory organizations. We illustrate the process in theory and in practice along the Central African Rift System (CARS), where data is sparse. This fault linkage systems approach has flagged underexplored areas where unmapped structure is likely that could, for example, be targeted with hi-resolution geophysical data. A similar system to CARS appears to cross southern Africa from Namibia to Tanzania - a “Southern Trans-African Rift system" or STARS. Exploration in the eastern Owambo Basin resulted in the mapping of a pull-apart basin from depth-to-basement inversion of high-resolution magnetic data and subsequently studied with structural modeling. Thinking in terms of such fault and structural systems, this ‘Kavango Basin’ can be related along strike to the Karoo Basins in Eastern Africa via features such as the Omaruru lineament, implying the possibility of a fairway of extensional basins and shears across the continent that are not obvious in existing low-resolution data. STARS represents a blue-sky frontier concept for both conventional and nonconventional exploration potentially offering new exploration leads, the ultimate objective of big picture work.
Fluids identification in reservoirs that bear low or mixed formation water salinity poses a challenge for reservoir management in terms optimum well placement strategies and reservoir surveillance. The logging industry provides many technologies to help characterize in-situ fluids while drilling or during the production stage.
An integrated reservoir engineering team has established an integrated formation evaluation methodology to identify fluids encountered in the reservoir, while drilling or while monitoring saturation changes periodically in key observation wells. A number of new and re-entry wells were selected to measure fluid saturation while drilling via different saturation tools; namely, resistivity, nuclear magnetic resonance (NMR), formation pressure testing and fluid sampling, and advanced mud gas logging to complement each other. Carbon/oxygen (C/O), coupled with a flowmeter survey, were run in two observation wells, in both flowing and shut-in conditions, and showed positive results for enhacing the capability to monitor saturation.
Following a comprehensive evaluation of all acquired data and interpretation, the petrophysical model was calibrated using NMR and downhole fluid samplings. Results have enabled building fluid characterization criteria for low contrast salinity clastic rocks based on reservoir complexity and fluid uncertainty.
The optimized C/O acquisition helped with analyzing fluid saturations and building an intriguing process to address challenges related to different environmental conditions. This evolved methodology revealed a more consistent saturation mapping with the actual reservoir understanding while identifying the optimum completion and excellent wellbore conditions for such a method.
The established fluid identification process, while drilling, will help optimizing well placement and well completion to yield productive wells. The customized C/O log process will enhance reservoir surveillance and monitor saturation change to assess sweep efficiency and overall field performance.
TOTAL E&P Angola organized, from the 13th to the 15th of November 2013, a large scale oil spill response exercise, called “LULA”. The oil spill strategy for the response to a 50 000 bopd blow-out scenario in deep offshore Angola was implemented. Offshore resources were actually deployed and tested, including subsea response with a newly developed subsea dispersant injection system mobilized from Norway and operated from a newly designed and built Light Well Intervention Vessel, and surface response (dispersion, containment and recovery). The implementation of an onshore response plan, encompassing shoreline protection and clean-up, waste management and oiled wildlife response, was simulated. This exercise provided a unique opportunity to mobilize simultaneously a wide array of oil slick monitoring techniques at sea. The assessment of their domains of application and effectiveness was made possible thanks to a special permission given by the Angolan authorities to release a limited amount of crude oil at sea surface.
Daily monitoring was implemented to assess the drift and behavior of the spilled oil and to guide resources during the response operations. Several technologies were tested. Drifting buoys were launched to reflect the oil slick position in near real-time by satellite transmission. Aerial surveillance was carried out by helicopter and by fixed-wings OSRL aircraft (mobilized from Ghana) to provide detailed information about the oil slick (position, shape and location of thickest slicks). These techniques were complemented by one of the latest innovation of the TOTAL Group: the observation balloon BOOST. This balloon, fixed to a supply vessel, provides an overview of the slick from 150 m altitude through a camera which feeds back visible and infrared geo-localized images, thus enabling positioning the response vessels on the thickest parts of the slick and initiating response at first daylight. RADAR imagery was also collected by satellite. A set of techniques enabling 5 days oil spill drift predictions is combined in another Company innovation: SPILLWATCH service, which includes 3D currents and winds forecasts, oil subsea/surface behavior and slick drift modeling, and daily recalibration using the RADAR images.
The results obtained during LULA demonstrated the consistency of the various techniques and confirmed the possibility to track a slick during day and night time.
Being able to follow spilled oil at sea is part of the Company’s responsibilities. These tests onsite will considerably improve our good practices and should benefit to the whole Oil & Gas Industry.
The southern Sudan rift basins form part of the Mesozoic Central African Rift System (CARS) and span an area 1000 km wide and 800 km along strike. They consist of two major NW-SE trending rift basins; the Muglad and the Melut. Following a series of gravity, magnetic and seismic related studies (Fairhead et al., 2012) most of the rift system’s kinematics and structural evolution are reasonably well understood.. However, ambiguities exist, where these rift basins coalesce towards the Kenyan border and the structural continuation and linkage to the Anza Rift (figure 1). This partly relates to a data gap across political borders.
This study (King, 2012) utilised the 5’ (~10km) and 1km grids of gravity and magnetic data from Getech’s African Gravity Project (AGP) and African Magnetic Mapping Project (AMMP). The ground gravity station distribution is shown as red dots and the aeromagnetic surveys are shown by the blue polygons in Figure 2. The regional rift basin setting is given by Figure 1 and shows the uncertain relation between the South Sudan rift basins and the Anza rift basin in Kenya.
These data sets were interpreted using a range of techniques to provide an integrated robust regional interpretation that reveals insights into the rift evolution of South Sudan and northern Kenya. The principal findings are evidence for an E-W trending shear zone linking the South Sudan basins to the Anza Rift, and the identification of a discrete N-S oriented basin related to a small shear zone in South Sudan.
Pan, Xiao-Hua (Research Inst. of Petroleum Exploration and Development, PetroChina) | Yuan, Sheng-Qiang (Research Inst. of Petroleum Exploration and Development, PetroChina) | Ji, Zhi-Feng (Research Inst. of Petroleum Exploration and Development, PetroChina) | Hu, Guang-Cheng (Research Inst. of Petroleum Exploration and Development, PetroChina) | Liu, Li (China Petroleum Engineering & Construction Corp, PetroChina)
With the exploration activities of China National Petroleum Corporation (CNPC) in Sudan, Chad and Niger, more and more 2D, 3D seismic data had been required, a series of exploration and appraisal wells had been drilled, and more of other geologic materials had been obtained, such as well logs, core, geothermal gradient data, geochemistry data etc. Based on these abundant data and integrated application of geophysics method, physical modeling, computer modeling and geological analysis etc., the authors carried out an in-depth study on the Western-Central African Rift Basins (WCARBs), coming up with an understanding that the Basins are of passive rifts different from the so-called active ones formed in result of mantle up-welling. The WCARBs present unique petroleum characteristics including low geothermal gradient, aggregate thin-bedded hydrocarbon source rocks in syn-rift sequence, small-scaled post-rift sequence and high-angle basin-controlling major faults etc., and as a result, exhibit petroleum systems with unique characteristics, such as late and long-lasting oil generating window, high oil-expulsion efficiency, and fault-block dominated traps with rare rollovers etc. The deep study and analysis of the basin structure, sedimentary features and petroleum system obviously enhance the exploration discovery of WCARBs, which is the key factor of the successful E&P activities of CNPC in WCARBs.
The evaluation of fault sealing is an important step in the calculation of fault trap reserve. When it comes to the issue of complex 3-D fault trap structures and thin reservoirs, how to appraise and calculate the reserve properly and effectively is still a subject that needs further researching. In this respect, a certain rift basin that has experienced multi-periods rift movement and evolved in a fluvial faces and braided deltaic depositional environment has been chosen as the object of our research on fault trap evaluation and calculation of reserves. The method has been preformed in the following steps. 1) The tectonic evolution and the structural characteristics of the studying area are accomplished through 3-D seismic interpretation; 2) Based on the results of the well to seismic combination, the provenance direction sedimentary system interpretation and sedimentary evolution are completed; 3) On the basis of achievements of the tectonic evolution and sedimentary evolution interpretation, the 3-D fault trap geologic model is established by spatial interpolation. A certain method invented by Li Qingzhong is employed to forecast the fault trap reserves quantitatively. Moreover, this method can be described as follows. Constrained by the seismic horizons, fault data and sedimentary isochronous interfaces, the connected sand body units in every depth slice of the 3-D fault trap geologic model can be identified automatically. Meanwhile, their sealing degree and connectivity is appraised quantitively from the top slice to the bottom slice. Finally, through quantitative calculation of reserves for fault trap, the effective forecasting of reserves has been achieved. The results of our work have testified that this appraisal method can be applied to improve the prospecting accuracy and reserve forecasting precision of fault trap reservoirs.