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Asia
New Opportunities From 4D Seismic And Lithology Prediction At Ringhorne Field, Norwegian North Sea
Johnston, David H. (ExxonMobil Production Company, Houston) | Tiwari, Upendra (ExxonMobil Exploration Company, Houston) | Helgerud, Michael B. (ExxonMobil Exploration Company, Houston) | Laugierz, Bernard P. (ExxonMobil Production Company, Stavanger)
Summary Time-lapse (4D) seismic data from the Ringhorne field in the North Sea are used to monitor water movement in both Paleocene and Jurassic age reservoir sands, improve existing geologic and simulation models, and enable more cost-effective field operations. The structural complexity of the reservoirs, their proximity to the high-impedance Cretaceous chalk, and a relatively small 4D response required a significant effort in seismic acquisition and processing which resulted in a highly repeatable survey. In addition to the 4D interpretation, Vp/Vs derived from simultaneous elastic inversion is diagnostic of sand and provides additional constraints on Ringhorne subsurface models. Connected volumes based on Vp/Vs correlate to areas of water sweep seen in the 4D data and reduce uncertainty in 4D interpretation. Relative P-wave impedance changes calculated from inversion are consistent with pre-survey 4D predictions. The 4D seismic and inversion results help explain water breakthrough timing and improve our understanding of field production history. The data have resulted in an increase in the reserves base and the identification of additional infill well opportunities.
- Europe > Norway > North Sea > Central North Sea > Utsira High > PL 169E > Block 25/8-11 > Balder Field > Statfjord Formation (0.99)
- Europe > Norway > North Sea > Central North Sea > Utsira High > PL 027 > Block 25/8-11 > Balder Field > Statfjord Formation (0.99)
- Europe > Norway > North Sea > Central North Sea > South Viking Graben > PL 103 > Block 25/8 > Jotun Field > Ty Formation (0.99)
- (41 more...)
SUMMARY A heavy oil field in the Sultanate of Oman is being developed using steam-injection EOR methods. A geophysical surveillance pilot was started to identify the best monitoring solution for field-scale deployment. Baseline surface seismic, 3DVSP and cross-well surveys have been acquired and processed. Surface seismic is very challenging in the area due to complex near-surface conditions, multiple contamination and weak target formation reflectivity. On the other hand, 3DVSP and cross-well surveys allow us to get clear images of the target reservoir after application of the experimental processing approaches. For cross-well data, the use of sources and receivers below the targets and down-going reflections delivered the image of the interval of interest, whereas there was almost no use in sources and receivers above the targets. This was not expected originally and highlighted the importance of considering ’illumination from below’ as an option in pre-survey modeling. The extensive multiple presence in the field impacted the 3DVSP images created with the use of space-domain deconvolution of up-going signal with a filter derived from downgoing waves. In order to suppress multiples more efficienly, we developed and applied ’interferometric deconvolution’ in the wavenumber domain. This deconvolution approach led to a cleaner image of the target. The results highlight the importance of downhole seismic in such fields and demonstrate the value of the field-adaptive data processing.
- Asia > Middle East > Saudi Arabia > Eastern Province > Al-Ahsa Governorate > Arabian Basin > Widyan Basin > Ghawar Field > Haradh Field > Lower Fadhili Formation (0.98)
- Asia > Middle East > Saudi Arabia > Eastern Province > Al-Ahsa Governorate > Arabian Basin > Widyan Basin > Ghawar Field > Haradh Field > Khuff D Formation (0.98)
- Asia > Middle East > Saudi Arabia > Eastern Province > Al-Ahsa Governorate > Arabian Basin > Widyan Basin > Ghawar Field > Haradh Field > Khuff C Formation (0.98)
- (4 more...)
Summary For the last 15 years, KOC has designed and acquired several 2D and 3D seismic surveys. These surveys progressed from the conventional sparse and dense to the single-sensor high-resolution acquisitions. Most of which were narrow azimuth and limited offset designed for a specific target. Recently KOC acquired a single-sensor full azimuth and long offset seismic pilot survey with the objective of assessing the optimum design required for future surveys, also the use of the surface seismic for fracture detection. Although there have been a major increase in the available channel-count in the industry it is still a challenge to optimally design the perfect 3D survey for KOC multitargets which range between 7,000 to 20,000 ft. In this study, we will review the recent advances in land seismic recording equipments and the impact of the available channel-count and sensor types in increasing the options for designing the optimal 3D land seismic acquisition in Kuwait. Introduction Kuwait Oil Company (KOC) has always been an early adopter of new technologies. In 1996, KOC started to acquire a 3D seismic program in Kuwait totaling 4,850 sq. km. covering most of the Kuwait onshore oil fields with the objective of better imaging the Cretaceous reservoirs. The 1,200 channels used then were considered extravagant at that time. The acquired data was considered to be of excellent quality but has limitations: narrow azimuth, short offset of 3,600 m, large (50 m) spatial source and receiver arrays. In 2002, a 30,000 channel single sensor acquisition system was introduced to Kuwait. Since then, KOC has successfully acquired and processed eight single sensor 3D seismic surveys totaling 3,680 sq. km. including a fullazimuth long offset 3D survey. The main objective of the full-azimuth survey was to acquire a seismic data set that could be analyzed to assess the most suitable acquisition geometry for the forthcoming exploration surveys of KOC with objectives that include imaging and characterizing deep Paleozoic targets. Future land 3D seismic data acquisition in Kuwait has several objectives to address; this includes imaging the shallow horizons for statics determination, imaging the deep reservoirs at depth of 20,000 ft and achieves the highest resolution to map the intra-reservoir of Cretaceous section. Other objectives are to minimize the geometry foot prints to enable successful attribute analysis and produce data sets ready for AVOA, inversion, etc. and the full azimuth for anisotropy studies and fracture characterization. Because of the relatively small land area of Kuwait (17,820 sq. km.), the large number of structurally similar fields and prospects (Figure 1), it makes sense to consider one land 3D acquisition template that addresses the requirements listed above and enables future seamless merging of all individual surveys to produce a single 3D volume covering the whole of Kuwait. Acquiring a perfect full fold 3D land P-wave survey to meet all requirements in Kuwait would require a large number of active channels, (Rached 2007). Several authors have discussed issues relating to acquisition to better sample the seismic wavefield and improve data resolution.
- Energy > Oil & Gas > Upstream (1.00)
- Government > Regional Government > Asia Government > Middle East Government > Kuwait Government (0.49)
Summary The Tulip 3D survey is a single-vessel full-azimuth Coil Shooting project in Indonesia. The circular geometry is very different to the conventional race-track towed streamer approach. While it results in many acquisition and imaging benefits, it also introduces a number of new challenges in the survey design, modeling, acquisition and processing workflows. This paper presents an overview of the data processing / imaging experience made during the coil shooting project. A processing workflow was tailored to address the challenges, and at the same time taking advantage of the opportunities provided by the circular geometry. The resulting images are demonstrably far superior to the vintage seismic data in the area, and provide a more suitable dataset for AVO inversion to seismic attributes and reservoir property characterization. Introduction The Tulip survey is located in the Bukat PSC block east of Kalimantan Island, offshore Indonesia. The field is located in a water depth of 350-1500m over the continental slope. The survey area is geophysically very complex due the presence of several unfavourable geological factors, especially in the near surface. Complex subsurface geology further complicates the scenario. All these conditions when combined, result in very strong and high orders of surface multiple reflections and diffracted multiples, absorption, scattering and poor transmission of seismic signal energy. Furthermore the reservoir has a very low acoustic impedance contrast. The consequences of these complexities is poor overall seismic response, very low amplitude or near invisible target reflections, very low signal-to-noise ratio (S/N), poor imaging and poor illumination of the reservoirs. In order to achieve a better imaging of the zone of interest and reservoir characterization for the reservoir appraisal campaign, eni successfully acquired a Coil shooting (French, Cole, 1984; Durrani et al, 1987) survey on the Tulip discovery in August-September 2008. The depth imaging of the survey was completed in January 2010. The circular geometry introduces several differences and new challenges in survey design, modeling, acquisition and processing workflow (Reilly, Hird, 1994; Reilly, 1995). For Tulip survey, a careful pre-survey modeling and processing simulation was critical to evaluate the feasibility of future post-acquisition processing of the survey, with respect to both the geophysical challenges and the geometry induced constraints and opportunities. When processing a Coil shooting survey, the first difference, compared to the conventional data, is the presence of the turn noise due to acquiring data while the vessel and cables are tracking continuously in circles. The level of noise is inversely proportional to the curvature radius of the circles being acquired and proportionally related to any apparent crossflow of currents. Another aspect which in certain conditions can become critical is the presence of statics related to the differences in water column velocity during the survey. A third very important feature and very different to the conventional processing is spatial sampling; with the Coil shooting geometry, the spatial samples are along a series of arcs instead of straight line and trace offset distances are not regularly spaced in the shot or midpoint domain.
- Asia > Indonesia > Northeast Kalimantan (0.42)
- Africa > Middle East > Egypt > Nile Delta (0.42)
- Asia > Indonesia > Northeast Kalimantan > Tarakan Basin > Tulip Field (0.99)
- Asia > Indonesia > Kalimantan > Tulip Field > Tulip Well (0.98)
Edge Preserving Vector Filter For Smoothing Reflector Dip And Azimuth
Wang, Wei (Institute of Wave and Information, Xi'an Jiaotong University) | Gao, Jinghuai (Institute of Wave and Information, Xi'an Jiaotong University) | Chen, Wenchao (Institute of Wave and Information, Xi'an Jiaotong University) | Zheng, Hui (Institute of Wave and Information, Xi'an Jiaotong University) | Zhang, Erhua (the Exploration and Development Research Institute of Daqing Oilfield Company Ltd)
Summary This paper proposes an edge preserving vector filter (EPVF) for smoothing seismic dip and azimuth computed by the finite-difference method. Our approach is composed of three steps: (1) set a reference direction, (2) invert opposite vectors to convert directions into orientations, and (3) smooth vectors with the EPVF. Inspired by Tomita’s multiwindow analysis technique, the EPVF divides the vicinity of every location in a 3D vector field into a number of subwindows as the analysis point moves throughout the volume. At an interior discontinuity location within any 3D orientation field, the EPVF utilizes the most centralized neighboring orientation instead of simply averaging across the edge. The proposed smoothing scheme preserves lateral and vertical geological boundaries in the resultant seismic dip and azimuth, which lead to increased resolution of wellestablished algorithms such as structurally oriented filtering, volumetric estimates of seismic reflector curvature and angular unconformities. Experimental results of a real seismic data example demonstrate the efficiency of our approach. Introduction Seismic reflector orientation (dip and azimuth) has broad applications, such as structure-oriented smoothing (Fehmers and Hocker, 2003; Lavialle et al., 2007), coherence and edge detection algorithms (Luo et al., 1996; Marfurt et al., 1998; Marfurt et al., 1999) and volumetric curvature attributes (al-Dossary and Marfurt, 2006). In addition, seismic reflector orientation itself provides stratigraphic and geographic information and is a valuable interpretation tool (Dalley, 2008). Several techniques have been proposed to compute the volumetric seismic reflector orientation (Marfurt, 2006). However, some of these techniques may suffer a loss of resolution and some bear high computational cost. The finite-difference method is an easy way to compute seismic dip and azimuth, which can be calculated directly from gradient vectors of stacked seismic data. However, it is a first-derivate operation and therefore tends to amplify highfrequency noise. A smoothing scheme is needed to suppress the noise and extract the large-scale features. Although calculating gradient vectors of the input data with finite-difference method is straightforward, smoothing this vector field is nontrivial. A wavefront has two opposite normal directions, and the orientation is one of them. For example, both 0° and 180° dips represent horizontal events, but their average ( 90° ) is vertical. Therefore, raw directions cannot be taken for a smoothing operation unless some maneuvers are used. One possible approach to overcome this difficulty is the gradient structure tensor (Randen et al., 2000; Fehmers and Hocker, 2003; Luo et al., 2006). The eigenvector corresponding to the largest eigenvalue will by definition best represent the variability of the seismic data and therefore will be aligned with the vector normal to the reflector events. But the gradient structure tensor approach may fail, when a dominant eigenvalue does not exist and the wrong eigenvector is selected to determine the reflector orientation (Wang et al., 2008a). Seismic Dip and Azimuth Smoothing with EPVF There are various vector filters designed for edge and detail preserving purposes, such as vector median filter, basic vector directional filter (Lukac et al., 2005).
- Asia > China > Heilongjiang > Songliao Basin > Daqing Field > Yian Formation (0.99)
- Asia > China > Heilongjiang > Songliao Basin > Daqing Field > Mingshui Formation (0.99)
Identifying Jurassic Tight Gas Sands In the East Texas Basin With 3D-3C Seismic Data
Valentin, Diego Alexander (Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin) | Tatham, Robert H. (Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin)
Introduction Summary The York sandstone member and other sandstone bodies within the Bossier Formation are characterized by having low porosity and permeabilities (6% and 0.2-0.001md respectively); they are Upper Jurassic in age in the East Texas basin and have been a target for dry gas since the late 90’s. Here we present the results of petrophysical analyses of five wells with dipole sonic logs, together with a detailed join interpretation of conventional PP and converted PS seismic data to infer the distribution of these Jurassic sand bodies. The objective is to guide new development wells in the Bossier Fm., at the East Texas Basin. The results of the petrophysical analysis suggests that despite of the low impedance contrast and some overlap of Vp/Vs values, this ratio could be used as a lithology indicator where low values of Vp/Vs ratio (1.55 or less) are expected for clean dry gas sandstones and values larger than 1.6 are related to silt and shale lithologies. From the join interpretation, the seismically extracted interval Vp/Vs ratio between the correlated Cotton Valley Limestone and Bonner member tops (an interval including the York sandstone), it can be concluded that there are zones where anomalously low Vp/Vs ratio (<1.6), may indicate catchment places associated to topographic lows where major sandstone bodies could have been deposited. Despite the fact that some of the most productive wells do not show anomalously low Vp/Vs values, the map does show pathways of relative low Vp/Vs ratios (<1.8), that can be associated with sandstones bodies encased in shale lithologies (>1.9). The Bossier Formation (Figure 1), part of the Cotton Valley Group (Upper Jurassic), has been of interest as a gas target since late 90’s, in the East Texas Basin. In particular, the upper part of this formation has productive gas sandstone units that have a SW-NE trend of gas fields located in Roberson, Freestone, Leon and Anderson counties, Texas. These fields have produced more than one TCF of dry gas to date. The study area is the Tennessee colony field located in the western portion of the Anderson County, Texas. Geologically the Tennessee Colony field is located in the oil and gas productive East Texas Basin (Figure 2). For this study we used dipole sonic logs and basic well logs from five wells, one multicomponent VSP covering the depths of interest, one time-migrated 3D seismic volume data of conventional PP data (72 miles2, Figure 3), and one time-migrated P-SV converted 3D volume (9 miles2, Figure 3). We performed a correlation process and followed the procedure to analyze multicomponent data described by Tatham (1985), and Tatham and McCormack (1991). The main objective was to test the capabilities of deriving interval Vp/Vs ratio as a lithology discriminator; this took into account that attribute extractions from the conventional PP 3D seismic volumes have not been effective indicators of the distribution of the sandstones bodies, possibly due to problems of vertical resolution at the level of the Bossier Formation.
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.58)
- North America > United States > Texas > East Texas Salt Basin > Tennessee Colony Field (0.99)
- North America > United States > Louisiana > East Texas Salt Basin (0.99)
- North America > United States > Gulf of Mexico > Gulf Coast Basin (0.99)
- (2 more...)
Integrated Interpretation Techniques For Detection of Fracture Corridors - An Essential Play Element of Hydrocarbon Potential For a Tight Carbonate Reservoir In Southeast Kuwait
Arasu, Raju T. (Kuwait Oil Company) | Al-Ajmi, Mohammad T. (Kuwait Oil Company) | Singh, Sunil K. (Kuwait Oil Company) | Dey, Arun K. (Kuwait Oil Company) | Al-Adwani, Talal F. (Kuwait Oil Company) | Devlikanov, Kasym (Schlumberger)
Introduction Summary Fractures in carbonate rocks play important role in producing commercial quantity of hydrocarbon. The fracture potential of a deeper carbonate reservoir in Burgan-Arifjan area located in southeast Kuwait is evaluated by an integrated approach. Based on structural seismic attributes, geomechanical model and core data minor fault/fracture trends having different azimuth orientations are mapped with high resolution in 3D seismic using advanced techniques. The resulted fault cubes are interpreted to identify possible fracture pods and corridors where the reservoir is likely to have improved bulk porosity. Greater Burgan structural complex consists of Magwa structure in the north, Burgan in the south, Ahmadi in the east and Arifjan structure in the southeast (Figure 1). Commercial presence of hydrocarbons is yet to be proven in the deeper section below the established reservoirs of Cretaceous age in Burgan-Arifjan area. Out of six deep wells drilled in early 80?s on Burgan structure, two wells produced oil on initial testing from a carbonate layer of pre- Cretaceous age which is the focus of the study. Analysis of core and reservoir engineering data elsewhere in Kuwait suggests that fractures in this reservoir contribute to porosity and permeability and thereby, productivity (Singh et al., 2009). No fracture data such as image logs is recorded in the wells in the study area but for the one drilled on Arifjan structure. The latter has struck oil in another pre-Cretaceous reservoir deeper by about 1200ft. Seismic Input Brief Geology The carbonate reservoir rock discussed in this paper occurs at a depth below 10,000ft (3000m) in the study area. It has a thickness of 140 to 180 ft and is deposited in ramp setting in shallow to deeper marine conditions. It is generally argillaceous, almost with no primary porosity. Structure maps at deeper levels prepared from 2D seismic depict Burgan as a simple anticline. Based on this model pre-Cretaceous exploration have been carried out on this structure so far. Greater Burgan area, excluding Arifjan in the southeast, is covered by 1350 km2 of 3D seismic data. The PSTM processed volume has a bin size of 25x25m. Arifjan area is covered by 300 km2 of Q–Land data, acquired and PSTM processed in 2007–09 with bin size 12.5x12.5m. Sample interval is 4ms for both. S/n ratio is fair to good with minimum multiple interference in the target interval of 1400–2400ms TWT. Structure and Tectonics 3D based attribute maps show the complexity of the structuring at greater depth in the area. The structures have apparently evolved by manifestation of multiple episodes of tectonics (Figures 2 & 3). A pair of high trends separated by a graben are oriented in north–south direction. Magwa and Burgan structures are bounded on the west by longitudinal reverse faults formed under compressional regime. Prominent northwest–southeast structural alignment is also seen. In the east, northward trending Ahmadi–Arifjan ridge is formed in association with thrust. East–west cross trends associated with strike-slip movement are superposed over the existing structures.
- Geology > Structural Geology > Tectonics (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology > Fault > Dip-Slip Fault > Normal Fault (0.35)
- Asia > Middle East > Kuwait > Ahmadi Governorate > Arabian Basin > Widyan Basin > Greater Burgan Field > Wara Formation (0.97)
- Asia > Middle East > Kuwait > Ahmadi Governorate > Arabian Basin > Widyan Basin > Greater Burgan Field > Ratawi Formation (0.97)
- Asia > Middle East > Kuwait > Ahmadi Governorate > Arabian Basin > Widyan Basin > Greater Burgan Field > Mauddud Formation (0.97)
- (13 more...)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Carbonate reservoirs (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Faults and fracture characterization (1.00)
Summary From the sixties of last century, a series of geophysical surveys had been launched in northeastern continental margin of the South China Sea (SCS) and a lot of study of geological structure features about Mesozoic in this zone had been carried out. Many researchers have presented the view of existance of Mesozoic, and made certain the reflection beneath the one of Cenozoic in the seismic sections to be Mesozoic, which was thought as the product of early rift. In the early acquisition of seismic data, most of the settings of acquisition time and parameters were aimed at Cenozoic. Great limitation exists in such sections to reveal the Mesozoic strata, and just in some sections Mesozoic can be identified. This situation makes it very difficult to depict the feature of Mesozoic completely through seismic data. Chen Bing (2004) calculated the thickness of Mesozoic in Chaoshan Depression through the inversion of gravity data in the restrain of seismic data, which promoted the study of Mesozoic in this area. But the cognition of Mesozoic in northeastern continental margin of SCS should be known from a larger scope. In recent years, geophysical data (gravity, magnetic and seismic) have been newly acquired in northeastern of SCS. The quality of seismic sections has gained great improvement, with the enhancement of the technique of gathering and processing. Studies also reveals that ( Liu Zhaoshu et al., 2002 ), in Pearl River Mouth Basin, magnetic basement is basically consistent with the basement of basin, except some shallow interference of magnetic body. Thus, we can calculate the distribution of thickness of Mesozoic in this key zone through joint inversion of gravity and magnetic data, in the restrain of Mesozoic bottom revealed from those seismic sections with high quality. Method Our goal is to calculate the thickness distribution of Mesozoic, through the fully use of gravity and magnetic data and meanwhile in the restrain of seismic data. A complete flow which would be well fit to this zone have been studied to achieve it. Besides the normal process, two key contents are included: three process to potential field data and joint inversion of gravity and magnetic data in a two-interface model. 1. Three process to potential field data (1) Reduction-to-the-pole (RTP) of Magnetic Anomalies at Low Latitude Study area locates in the low latitudes, and the magnetic anomalies observed here are more complicated than the ones in high latitudes, for more random noise are involved in the field data. Serious distortion will occur in the result if simple process of RTP is taken. In order to resolve this problem, Wu et al. (1992) introduced the method of filtering, high resistance filter is used in the high frequency and anti-Hanning window filter is used in the low frequency. This process raises the S/N ratio and considers the effect of bias of magnetic inclination. Yao et al. (2003) proposed a new suppression filter, which is designed to suppress specific frequencies to solve the problem.
- Geophysics > Seismic Surveying (1.00)
- Geophysics > Magnetic Surveying (1.00)
- Geophysics > Gravity Surveying > Gravity Modeling > Gravity Inversion (0.67)
Application of P-wave Azimuthal Anisotropy For Fracture Detection In a Volcanic Reservoir
Zhan, Yijie (LandOcean Energy Services Co., Ltd) | Chen, Shumin (Exploration and Development Research Institute, Daqing Oilfield Co. Ltd) | Jiang, Chuanjin (Exploration and Development Research Institute, Daqing Oilfield Co. Ltd) | Zhang, Erhua (Exploration and Development Research Institute, Daqing Oilfield Co. Ltd) | Ju, Linbo (Exploration and Development Research Institute, Daqing Oilfield Co. Ltd) | Li, Mei (Institute of Sedimentary Geology, Chengdu University of Technology)
Summary: We present a case study of fracture detection using a 3-D P-wave seismic dataset from the Xujiaweizi (XJWZ) fault depression in the northern Songliao Basin in China. With the discovery of more volcanic gas-bearing reservoirs in XJWZ fault depression, we have realized that the most critical uncertainty in optimizing reservoir production is the location and characterization of the natural fracture system. Traditionally, fracture information comes from well data, in particular, image log (FMI) and core. This paper describes how p-wave azimuthal anisotropy can extend the characterization of fractures in volcanic (and other) rocks to regions between the wells. A major aspect of this study is to compare and contrast on a common dataset the effectiveness of different seismic azimuthal attributes in characterizing fractures and quantify those differences. Results indicate this is an effective approach for fracture detection and characterization in volcanic rocks. The final fracture orientation and density maps calculated from the p-wave azimuthal anisotropy are consistent with FMI interpretation and coring data from drilled wells. Introduction: It is universally acknowledged that sub-vertical natural fractures can dramatically increase the permeability and (to a lesser extent) the porosity of reservoirs. In many cases fractures result in preferred directions of flow and are required for commercial gas or oil production. Because of increasing awareness of their importance, many methods have been used for fracture detection, such as tectonic stress analysis, shear-wave splitting, coherency, structural curvature, etc. This paper describes how to best use azimuthal anisotropy in 3-D P-wave data to map the distribution of naturally fractures in a volcanic reservoir in the XJWZ depression of the Songliao Basin. Not surprisingly, we have noted a close relationship between the fractures and tectonic movements. Forward Modeling Aligned fractures in a reservoir, cause anisotropy in seismic attributes such as frequency, amplitude and impedance (see, for example, Al-Hawas et al.,2003). So, if we assume a single set of aligned vertical fractures in a deep volcanic reservoir is aligned and consists of one major orientation, the azimuthal differences of P-wave seismic attributes, such as velocity, frequency and amplitude, can be described as an ellipse (Li et al., 2003). Depending on the attribute being considered in this simple 2-D model, either the long axis or short axis of the ellipse indicates the fracture orientation. The relative ratio of the long to the short axes of this ellipse can be considered an indicator of fracture density, which represents the number of fractures that intersect a scan line of a given length. Since the seismic trace consists of changes in impedance contrast rather than velocity or density individually, we have to establish the link between the orientation of fractures and seismic impedance. We present two cases that are directly associated with the seismic. However, if p-wave propagation is perpendicular to the fracture, impedance A will remain unchanged but B will be significantly lower than 14,000. Then we can use the ratio of the ellipse axes to indicate the differences of impedance between different azimuths.
- Asia > Middle East > Saudi Arabia > Riyadh Province > Wudayhi Field (0.99)
- Asia > Middle East > Saudi Arabia > Eastern Province > Wudayhi Field (0.99)
- Asia > China > Heilongjiang > Songliao Basin > Daqing Field > Yian Formation (0.99)
- Asia > China > Heilongjiang > Songliao Basin > Daqing Field > Mingshui Formation (0.99)
Summary Airborne magnetic, magnetic gradient and radiometric surveys were carried out for the Ministry of Mines, Mali, covering most of the known Birimien outcrop, for a total coverage of 186 168 line km. Selected areas were followed up with airborne time domain EM surveying, for a total of 26 042 line km. The surveys were carried out between December 2001 and May 2004. The work was followed up with comprehensive re-mapping of the entire surveyed area. Enormously enhanced understanding of the Malian Birrimian was achieved, including the generation of many mineral exploration targets for follow-up, and the delineation of a major dyke suite, previously unsuspected. The work was funded under the EU SYSMIN scheme. The data are available from the Ministry of Mines for commercial use for a nominal licensing fee. In consequence, there has been a dramatic increase in the level of mineral exploration activity in theMalian Birimien. Introduction The Ministry of Mines, Govt. of Mali commissioned a series of airborne geophysical surveys covering most of the known Birimien outcrop, using EU SYSMIN funding. Survey design and description Much of the known geology had N-S strike, but the magnetic equator passes through the area, giving rise to low-inclination geometrical anisotropy, and giving reason to fly closer to N-S. The primary magnetic/radiometric flight direction was therefore chosen to be SE/NW (135°/315°) at 400 m line spacing, with ties flown NE/SW at 3 km spacing. A flying height of 80 m ensured good radiometric count rates and resolution. The survey as conducted with two virtually identical systems, using Aerocommander aircraft. The magnetic survey used three magnetometers aboard each aircraft, on a tail stinger and both wingtips, to measure all horizontal gradients. The radiometric system was calibrated for elemental abundances. The EM surveys used the same line directions but otherwise followed standard GEOTEMTM specifications, and used line/tie spacings of 400m/4km. Coverage, QC, processing, results (magnetic and radiometric) Three separate areas were surveyed with the magnetic/radiometric systems (Bougouni, Kayes, Douentza). In addition, previous non-exclusive coverage of the Kenieba area (flown at 200 m/ 3 km line/tie spacing) was purchased outright and a sparse pattern flown over the area to permit back-calibration of the radiometric data to elemental abundance (Figure 1). The survey contract included very prescriptive start-up certification and fully specified QC requirements covering flying accuracy, height keeping, manoeuvre noise, magnetometer noise, magnetic diurnal/storm variation, and radiometric calibration and repeatability. In addition to a standard processing sequence, the radiometric data were subjected to NASVD processing and were reduced to elemental abundances and radiometric dose rate. The magnetic data processing was standard, except that gradient-enhanced gridding techniques were applied to the new magnetic data to reduced cross-line aliasing. We saw significant improvement in the data quality, despite the fact that the wing-tip magnetometers showed significantly more manoeuvre noise than the tail sensor. The improvement is demonstrated in Figures 2a and 2b. By way of illustration, figure 3 shows Magnetic anomaly and radiometric ternary images from the Kayes area.
- Materials > Metals & Mining (0.72)
- Energy > Oil & Gas > Upstream (0.51)