- Home
- Conferences
- Conference Proceedings
- Conferences
PGCE 2011
- Conference date: 07 Mar 2011 - 08 Mar 2011
- Location: Kuala Lumpur, Malaysia
- Published: 03 July 2011
81 - 100 of 104 results
-
-
4D Effect from Saturation Variation Due to Fluid Movement Using 4D Seismic Acoustic Impedance Inversion Methods for Reservoir Monitoring
Authors Shuhadah Basaharudin, Nor Azhar Ibrahim and M. Firdaus A. HalimInversion method is the process of extracting the acoustic impedance (AI) profile for each seismic trace. The AI property is related to the layer properties of the reservoir-density and velocity. Meanwhile, velocity and density data can be obtained from well logs. Therefore the impedance inversion relates the seismic data with the well log data. The purpose of this study is to understand the changes in reservoir properties that could be predicted from the changes in P-impedance between the two surveys (base and monitor) and to obtain a time-lapse impedance model that can predict changes in fluid distribution that is due to production of hydrocarbons and also due to water injection (EOR) over the well X. All inversion algorithms suffer from non-uniqueness because there could be more than one possible geological model consistent with the seismic data. However, we can include the low frequency model (LFM) to constrain the final result and give a reliable and accurate inversion output. Low frequency information can be derived from well logs information or from the stacking velocities. The benefits of seismic inversion are numerous such as the broader bandwidth of the impedance data maximizes the vertical resolution and minimizes the tuning effects, interpreting volumes rather than surfaces is geologically more meaningful, removes the effects of the wavelet from the seismic bandwidth, reservoir properties are separated from the overburden, may provide quantitative predictions on the reservoir properties and possibility of extending the layer features beyond the seismic bandwidth.
-
-
-
Channel Thickness Estimation Using Spectral Decomposition
The Spectral Decomposition provides a new, non-traditional approach to seismic interpretation and attributes analysis. This technique is used for imaging and mapping temporal bed thickness, channel and geological features over 3D volumes where the samples are subdivided into different frequencies ie; 10 Hz, 15 Hz, 20 Hz, etc (Kishore, 2006) . Different materials in the rock strata resonate at different frequencies, and therefore can be distinguished from one another by their frequency response. The Spectral Decomposition techniques is widely used and successfully done for channel thickness estimation in a field scale (Partyka et al., 1999, Hall, 2004). However, channel thickness estimation in a regional scale has not been widely done. This study is the first attempt in applying this technique in the Malay Basin with regards to the I group channel. This study covers an area of 40,000 km2 located in the southern half of the Malay Basin. As a control parameter the top I and top J were interpreted and 20 proportional slices were defined by using stratal slicing technique. For each interval the RMS amplitude was carried out to produce a channel map. The spectral decomposition technique was performed to estimate the channel thickness. 20 Spectral decomposition volume attributes were generated at each interval to estimate the channel thickness for I010 to I140 channels. The frequency range from zero to Nyquist frequency (125 Hz) was generated. In addition the frequency slice animator was used to review the Frequency tuning map to determine the Optimum Frequency (Fo). Subsequently, average velocity was utilized to calculate the channel thickness. As the conclusion it can be deduced that the Spectral Decomposition technique worked well in the study area where the results were found to be quite matched with the channel thickness value stated in the well information. For that reason, this technique was confidently applied to some areas that do not have any well control in order to perform the channel thickness estimation.
-
-
-
The Onshore to Offshore Dent Group, Eastern Sabah from Sequence Stratigraphic Perspective: Implication to Petroleum Exploration
The prospective Sandakan sub-basin has been less explored even though some oil and gas discoveries has been made in addition to the numerous thermogenic gas show encountered in most of the exploration wells in the offshore Eastern Sabah. The gas and condensate was tested with flow rate as high as 15mmcfg and 500 bc/d in one of the wells, however the discovery of commercial size has yet to be made. The probable reason for this lack of success is insufficient seal integrity due to very high percentages of sand vs. shale. Field observation of the Dent Group outcropping in Dent Peninsula shows the occurrence of thick shale belonging to Sebahat Formation, the equivalent to the main reservoirs in the offshore. This formation together with younger Ganduman and Togopi Formations are collectively known as the Dent Group of Middle Mioecene to Pleistocene. The Group consists of post-rift sedimentary packages, overlying the older syn-rift Segama Group. It consists of fluviodeltaic to marine sediments, characterized by strong southeastward progradation into the offshore area. The onshore to the offshore correlation of the Dent Group is achieved through application of sequence stratigraphy. The group can be divided into 2 mega-sequences that consist of several higher
order composite sequences, namely Composite-Sequence 1 and 2. The older Composite-Sequence 1, consists of lithological units that has been described as Sebahat and Ganduman formations, while the younger, Composite-Sequence 2 consists of the Togopi Formation. The occurrences and distribution of the lithofacies of the Dent Group can be explained through subdivision of the sequence into composite systems tracts. The lowstand sequence set of Composite-Sequence 1 mostly sub-cropping in the offshore area, while the Sebahat Formation in the onshore represents the transgressive sequence set. The Ganduman Formation is interpreted as the highstand sequence set of the sequence. The transgressive Sebahat Formation offers a new look for its sealing capacity as well as reservoir potentials. The thick Sebahat shale outcropping on the Dent Peninsula is occurring in the offshore as well, and potentially sealing. On the offshore seismic sections, this shale is observed overlying the transgressive carbonate and thick lowstand sequence set of Composite-Sequence 1, which contain good reservoir facies. The facies of the lowstand sequence set is interpreted to consist of turbidites forming the fan-system and stacks of shoreface deposits forming the lowstand set of prograding wedges.
-
-
-
Estimating Poisson’s Ratio from Elastic Impedance: A Case Study for Hydrocarbon Plays in Malay Basin
Authors Ang Chin Tee and Shaidin ArshadIt is now common for a 3D datasets to be processed as partial offset volumes to exploit the AVO information in the data. The amplitudes of near-offset stack relate to changes in acoustic impedance (AI) and can be tied to well logs using synthetics. Unfortunately, there have been no simple equivalent processes for far-offset stacks. However, the symmetry can be recovered using the elastic impedance (EI). EI provides a consistent and absolute framework to calibrate and invert nonzero offset seismic data just as AI does for zero-offset data (Connolly, 1999). An EI log acts as a platform to calibrate the inverted data to any desired rock property (SI, σ, μ, λ etc) with which it correlates (Connolly, 2010). Many studies on EI have been done on Gulf of Mexico, and a strong correlation was found between EI at 30° and hydrocarbon pore volume. This relationship was then used to estimate the in-place volumes for the field from the inverted 30° seismic volume. EI is also widely used to discriminate lithology and to distinguish fizz water from commercial gas concentrations (Gonzalez, 2004). Estimating the Poisson’s ratio from seismic is also crucial. Theoretically, one can invert a 90° angle stack which has amplitude that is proportional to changes in Poisson’s ratio. However, this
approach is difficult due to the sensitivity to residual moveout and bandwidth variations. On the other hand (refer to the equation above), EI has values equal to AI at normal incidence. If K = 0.25, then EI is equal to (Vp/Vs)2 at 90° which is closely related to Poisson’s ratio. This allows the construction of high angle stack, and then being calibrated and inverted using the equivalent EI log. Since the absolute level of EI(90°) is depending on the value of K being used, one should study for the optimum angle of EI that correlates with Poisson’s ratio at well locations. In this paper, we will perform this study for hydrocarbon plays in Malay Basin and validate the result by estimating the correlation coefficient. With the known optimum angle, we can estimate Poisson’s ratio from
seismic with the information from EI.
-
-
-
Challenging Views towards Minimization of Multi-Component Data Complexities
Authors Amar Ghaziah, Riaz Alai and Hafizal M. ZahirThe acquisition of seismic multi-component data and the application of various multicomponent processing technologies have shown observable benefits in more accurate imaging of the earth’s subsurface. Although many successful and advanced technologies have been applied in the oil and gas industry with compressional waves alone, the help of shear waves in addition to existing methodologies has opened new opportunities to many oil and gas companies in finding new reserves. In addition to improved subsurface imaging using shear wave information, they are also inevitable in optimal characterization of reservoirs. Complexities in multi-component data occur when the wave front suddenly gets distorted due to sudden subsurface velocity changes. An increase of velocities corresponds to waves reaching subsurface salt bodies or hard volcanic rocks. On the other hand, lower velocities are directly related to waves passing through gas clouds, which is characteristic in Malay Basin environments. In this abstract, some challenging views will be discussed for waves passing through gas clouds and some examples will be shown on field data from the Malay Basin. The critical observations include lower amplitude reflections and minimal propagation of compressional waves, which create serious complexities and challenges in optimal illumination and imaging within these environments. In this abstract, we review existing efforts and important characteristics of compressional waves as well as shear waves related to data from the Malay Basin emphasizing the added value of shear wave energy towards enhanced understanding and characterization of oil and gas reservoirs.
-
-
-
A Shallow Water CSEM Case Study: Qualitative and Quantitative Analysis
Authors Mazlan Md Tahir, Azani Abd Manaf and Siti Hassulaini Abdul RahmanControlled Source ElectroMagnetic (CSEM) has been proven to be a valuable tool for remotely detecting and mapping offshore hydrocarbon reservoirs. The method, described by Eidesmo et al. (2002), measures the electrical properties of the subsurface where replacement of saline pore fluids by hydrocarbons influences the resistivity of reservoir rocks. A CSEM survey was conducted in shallow water area (~90 m depth) where is located at the depocenter of the late tertiary west Luconia delta (Rajang delta), west of the Central Luconia Province, Offshore Sarawak, Malaysia. Generally, geological setting of the area is a regressive, prograding deltaic sequence interrupted by regional transgressive events Earliest Pliocene, Late Early Pliocene and Early to Mid-Pleistocene (Robertson Research, 1989). The basin deepened to the northwestern part of the survey area, where thick marine sequences were deposited during Neogene to recent. Receivers were deployed in two 3D grids to allow for inline and wide azimuth data covering
two main prospects which are 12 km apart. In addition, a single receiver line was deployed almost perpendicular to these grids to cover an elongated target not covered by the grids. The first pass analysis of the resistivity distribution was obtained through a qualitative approach (attribute analysis). This approach is limited to denoting one area more resistive than another, excluding actual resistivity values and accurate depth investigation. In shallow water, the measured data is dominated by an electromagnetic (EM) signal that has propagated along the air/water interface, commonly known as the airwave effect. The airwave effect in the data was reduced by decomposing the EM field into down going and up going component and removing the latter (Amundsen et al., 2006). After the airwave removal, the attributes obtained anomalous features over the prospect area, however this analysis is inconclusive. A quantitative (inversion) approach was later adopted, which can both account for the airwave and assign resistivity values in depth where sensitivity is provided. Anisotropic 2.5D and 3D inversion was applied and supported that the anomalous features observed in the qualitative approach coincide with high resistivity within the seismic prospect outlines. Even though both inversion
schemes (2.5D and 3D) reconstructed the resistive features, it is important to recognize the limitation of 2D data. A 2.5D inversion relies on a 2D approximation of the subsurface, rendering geometry changes orthogonally to the towline unresolved. A grid survey resolves 3D effects and anisotropy by combining inline and azimuth data, i.e. data from receivers both on and off the source towline (Morten et al., 2009).
-
-
-
Methods in Estimating Visco-Elastic Properties for Gas Cloud Imaging : A Multicomponent Seismic and Rock Properties Analysis
Authors Ang Chin Tee and M. Hafizal Mad ZahirThe presence of gas cloud in the Malay Basin has always been a topic to be discussed when it comes to imaging the subsurface. Gas cloud has caused compression (P-waves) data acquired to suffer from poor data quality due to higher attenuation of P-waves, wavefront distortion which caused by low velocity distribution within the gas bodies and transmission losses. Converted shear wave (P-S waves) data from multicomponent acquisition allows images to be obtained that are unobstructed by the gas and/or fluids (Thomsen et. al 1997, Granli et. al 1999). In addition, rock properties can be uniquely determined from the compressional and shear data, allowing for improved reservoir characterization and lithologic prediction. This paper will discuss method for determining the optimal parameters of the velocity (V) and density (ρ) within the gas cloud for further input into P-S waves imaging.
-
-
-
Integrating Sedimentological Core Study and Seismic Attributes to Define Fluvial Channel Characteristics in the Malay Basin
The integration of sedimentological core study and seismic attributes to define the fluvial channel characteristics has been carried out within the 3D seismic megamerge, in the seismic Group I, Malay Basin. The main objective of the study is to characterise the geometries, heterogeneities, properties, and classification of fluvial channel reservoirs in Group I. The study were carried out by utilizing the available cored intervals, biofacies analysis, wireline logs, seismic, and well data. The method used in this study is based on the core review program by evaluating the core-based results and integrating with the RMS seismic attributes results. The core review program utilizes both previous investigations as well as conducting new study on the cored sections. The cored interval included cores taken from the I-25, I-50, I-68, I-80, I-85, I-90, I- 100, and I-110 reservoirs, which were discovered from year 1978 to 2002. The depositional environments of the cored intervals were then interpreted based on the core lithofacies associations
integrated with biofacies characters from palynological and foraminiferal analyses.From the results of the core study, only cores from 3 wells have been identified as potential fluvial channel sandbody. The identified potential fluvial channels core data were later validated and verified with the available seismic data. The study has established new insights with implications on the understanding of the paleogeography of the Malay Basin for the I group. Based on the core facies analysis there are five main sandstone lithofacies identified from the fluvial channel facies of I25, I80, and I100 in Group I, Malay Basin. These are trough cross-bedded sandstone, massive sandstone, cross laminated sandstone, parallel laminated sandstone, and ripple laminated sandstone lithofacies. The best reservoir characteristics for the fluvial channels are shown by trough cross-bedded sandstone lithofacies. The core based characterization and classification of Group I have identified three key wells from reservoir I25, reservoir I80, and reservoir I100 as potential fluvial channel sand bodies. Specifically, comparisons are made as to properly integrating the core-based and seismic-basedinformation from horizon strata slice of RMS amplitude maps. The integrated study approach concludes that only two cored wells have been interpreted to penetrate fluvial channel sand bodies while other cores from Group I which were thought to be fluvial in nature based on previous work or their log profiles however indicate that they were deposited in more marine environments. The integration of sedimentological core study and seismic attributes has defined the fluvial channel classification in the Group I in the Malay Basin, capable of improving reservoir understanding.
-
-
-
An Appraisal Well, from Geophysical Point of View: Do Not Simply Call it a Failure!
Authors Hijreen Ismail, Prama Arta and Bernato ViratnoThe field is located around 148 km from Bintulu, Offshore Sarawak. This field was discovered in March 2006 by Z-1 exploration well. The type of reservoir is a carbonate pinnacle. The recently drilled appraisal well X-ST1, has opened various perspectives. The production tests in the three different zones failed to prove the availability of a significant amount of hydrocarbon in the northern part of the field structure. However the successful VSP operation, manage to provide a new time depth relationship at the well location. The success also offered velocity control at the northern area and allowed reinterpretation works. The latest well correlation sets a new geological marker, whereby the Top of carbonate was found to be ~26 m shallower when compared to prognoses. Five horizons were reinterpreted. They are Top of carbonate and Top of zone 4, 5, 6, and 7. Using the new generated 3D velocity model, all the TWT maps were then converted to depth structure maps. When the generated depth structure map of Top of zone 6 was overlaid with gas water contact as found in Z-1 well, a saddle, which separates the southern pinnacle from the northern area carbonate platform in this zone, appeared to be suggested. Hence new resource assessment exercises had been conducted based on the new gross bulk volume (GBV). Consequently, it was gladly found out that there are 69% increase of volume in terms of calculated 2P GIIP. The drilled X-ST1 well also provided input on the quality of the carbonate in the northern area. The porosity bserved in this well is totally different from the Z-1 exploration well. In conclusion the X-ST1 appraisal well did provide noteworthy inputs to the understanding of the field structure and economic values to the company.
-
-
-
Fit for Purpose Seismic Reservoir Characterisation
Authors Troy Thompson, Matthew Lamont, Carlo Bevilacqua and Natasha HendrickQuantitative seismic interpretation utilises seismic amplitude behaviour in conjunction with well log data, petrophysics and rock physics to make quantitative predictions about lithology and fluid away from well locations. Seismic reservoir characterisation in general cannot follow a one-size-fitsall approach – it is critical to consider local geological insight. It is also essential to determine the appropriate quantitative interpretation (QI) workflow based on available seismic and well data, and the desired outcome. Together, this will ensure robust and reliable characterisation of the hydrocarbon reservoir is achieved.
-
-
-
Application of Seismic Attribute for Channel Imaging in the Malay Basin
A seismic attributes is any measure of seismic data that help us visually enhance or quantify features of interpretation interest (Chopra and Marfurt, 2007). Amplitude, Frequency and Phase represents different aspect of a seismic reflection that brings outs different aspects of geologic features.The purpose of this paper is to document the application of seismic attributes for channel imaging in the Malay basin at basin wide scale. Presently, channel characteristic in the I-Group has not been fully understood. Therefore, the utilization of mega merged data for this project is to help us better understand of channel morphology/characteristics in the Malay basin through the application of seismic attributes. The area coverage of this study is approximately 40,000km2 which includes the 3D mega merged volume in the southern half of the Malay basin and fifteen (15) individual 3D seismic volumes. Two (2) major horizons, I-TOP and J-TOP were interpreted for basin-wide interpretation of I-Group interval as shown in Figure 1. From this, twenty (20) strata/proportional slices were generated using stratal slicing techniques that were associated to I010 to I140 sands of the I-Group. Seismic attributes analysis on a small volume was carried out to identify the best attribute for channel imaging. The result shows that Root Mean Square (RMS) attributes reveals the anomalous amplitudes which represent channels outline (Figure 2) while frequency volume created from Spectral Decomposition has further enhanced the channel images (Figure 3). Future similar works could be expedited using this methodology and better define the channel outline.
-
-
-
Gravity and Magnetic Signatures, Derived Crustal Structre and Tectonics of Sirt Basin, Northern Central Part of Libya
Authors Ahmed. S. Saheel, Abdul Rahim Bin Samsudin and Umar Bin HamzahThe Sirt basin is located in the north central part of Libya within the bounder's 270N-330N and 160E-220E. This study involves analysis of gravity and magnetic data to delineate structures and faults and to locate any major structures. The produced Bouguer gravity map shows prominent NW-SE and N-NW trends. Isostatic residual map is characterized by a dominant NW– SE trend in the study area. This is clearly evident in the isostatic residual. The main trending anomalies are in the northern and southeastern parts of the study area with NW-SE orientation. A strong NW-SE trend is truncated by E-W trending in the southeastern and southwestern parts of the area. This is consistent with change of tectonic zones (Duronio and Colombi, 1983). The magnetic expression in the northern part of Ajdabiya trough is characterized by NW-SE trending structures which coincide with late Cretaceous structures of the Sirt basin, while the southern part is characterised by NE-SW trending features which coincide with a late Paleozoic trend (Goudarzi, 1970, 1980). The northern part of the Ajdabiya trough is separated from the southern part by a prominent NE-SW lineament that is expressed in both the gravity and magnetic data. It is interpreted as a basement fault, which separates a thicker southern crust from a thinner northern crust. The high gravity anomaly within the northern part of the Ajdabiya trough is interpreted as a result of mantle upwelling which caused thinning of the continental crust beneath the northern part of the Ajdabiya trough. The Total horizontal derivative results of Gravity and Magnetic data (Cordell, 1979) ,(Cordell and Grauch, 1985), 3D Euler Deconvolution of gravity and magnetic data magnetic anomalies produced features trending similar to the positions of tectonic and geological information from the Sirt basin. High gradient values delineate NNW-SSE to N-S and NW-SE trends which mark the faulted southwestern, southern, northern and central boundaries of the basin, respectively. New faults with orientations NNW-SSE trends along the southwestern flank of the Sirt basin and is truncated by E-W faults dividing it into segments. Strong N-S lineaments occur over the southern and central part of study area and are well indicated by the 3D Euler Deconvolution. From this study the 3D Euler Deconvolution provides very useful information of the rift structures. Predictive modelling (2-1/2D) of gravity profiles was carried out for northern and southern parts of Sirt basin. Two profiles were controlled by wells. The deepest part of the northern profile is in the Ajdabiya and Al Jahamah platform and approximately depth from 3-6km. The deepest part along the southern profile is approximately 4.88 km in the Zallah and Hameimat trough.
-
-
-
Seismic Imaging and Velocity Modelling Offshore Myanmar (Andaman Sea Basin).
More LessAll Geophysical Data Analysis/Processes are basically solving the inverse problem. One of the inversion methodologies is to derive Structure & Velocity via Seismic Imaging. The proper seismic imaging workflow is crucial in attenuating multiples and optimally images the seismic feature. This will further enhance the confidence level during interpretation and mapping and might all the way lead toward seeing flares. From pre-analysis/data preparation/data stabilization, analysis/data processing to deliverable of Pre-Stack Time Migrated Gathers require detail and precise technical analysis. The testing of 2D seismic line no. A, Offshore Myanmar, Andaman Sea Basin through PSTM has shown optimized subsurface imaging and better attenuation of multiples, which
can be seen in target zone from 3000ms to 4000ms TWT.
-
-
-
Source of Coal Bed Methane
Authors Swapan Kumar Bhattacharya and Saleem Qadir TunioCommercial viability of a coal bed methane project exclusively depends on the available source of methane. By default it is expected that the source of methane is bacterial / thermal actions on organic biomass during coalification process. Carbon isotope signatures and chemical composition of the produced gases are not always favourable supports to the coal origin of the available methane. Moreover, all the major successful coal bed methane projects are geographically located over one or the other petroliferous basins. Does it mean that the coal bed methane has some intricate source relation with occurrence of petroleum?
-
-
-
Post-Stack Cross Equalization for Time-Lapse Seismic
Authors Tan Chin Kiang, Wahyudin Suwarlan-PCSB, Kartina Ali and Fariz FahmiSuccessful 4D imaging requires high repeatability. Repeatability is a measure of similarity of two or more vintages of seismic data and is a function of acquisition geometry, ambient conditions and processing similarity. This paper illustrates a case study to cross equalize two 3D datasets acquired in 1995 (base) and 2006 (monitor) in a field with pressure maintenance support to analyze whether technology can be used for reservoir monitoring purposes. Prior to the cross equalization effort, the base and monitor surveys were processed together using a 4D co-processing workflow. Co-processing is done with careful choice of parameters to maximize repeatability and optimize production-related 4D responses. The cross-equalization process is done after co-processing to minimize any seismic differences unrelated to production (improving repeatability) and enhancing the interpretability of the real 4D signal. This is also the process that generates the final 4D volumes and 4D attributes for the interpretation analysis. The key steps in the cross equalization workflow include residual phase matching, static time shift, matching filter, amplitude normalization and time varying time shift. The accuracy of co-processing and consistent acquisition minimized the level of required cross qualization. Appropriate QC at each stage of cross equalization ensures that the desired 4D effect is preserved as the two datasets become increasingly comparable and look alike in the non-reservoir zones where ideally no change is expected. The final differences after cross equalization clearly shows high amplitude 4D anomalies around injector wells. The overall improvement of 4% repeatability was achieved through the cross equalization process. The 4D data successfully imaged both water and gas movement throughout the major reservoir and results are currently being used to update the geologic and reservoir simulation models as well as to support a drilling campaign.
-
-
-
Seismic Facies Characterization of the Central Northwest Sabah Basin
The presence of reservoirs especially at the outboard of NW Sabah Basin is one of the major issues for the explorationist. Some of the wells were drilled targeting turbidites were unfortunately not successful. A total 15 regional 2D seismic lines from different vintages have been chosen as key lines for seismic facies description and facies mapping in order to established regional correlation from inboard to outboard Sabah and identify new hydrocarbon play, leads & prospects. The study area is located at the centre of NW Sabah Basin, which covered from inboard to outboard area. Generally the basin is bounded to the west by the West Baram Line & to the east by the Balabac Strait Fault. The Sabah Basin is a structurally complex basin that was form on the southern
margin of a foreland basin that resulted from the collision between the NW Sabah Platform and western Sabah during the early Middle Miocene. Its complex syn-tectonic sedimentary history resulted in the recognition of major unconformity-bounded sedimentary packages Stages IVA to IVF (Mazlan Hj. Madon et al., 1999). There are 4 major seismic facies characters had been identified, which displayed strong amplitude with wormy reflector, weak amplitude with wormy reflector, strong amplitude with parallel
reflector and weak amplitude with parallel reflector. Turbidite environment can be interpreted by identifying wormy reflector which usually represents channelized activity and also deepwater evidence such as gull wing character. Parallel reflector represents more quite and calm environment. (Walker and James, 1992). Integration of seismic characters with sequence stratigraphy approach will facilitate to interpret DOE and to produce paleo-environment map (Emery and Myers, 1996). This paleo-environment map will contribute to the petroleum system analysis within the area especially in term of presence and reservoir distribution prediction. Ultimately, this map would be able to explain why certain well is successful or vice versa.
-
-
-
Geological Mapping Using Remote Sensing and Magnetic Data
In this project, Thematic Mapper (TM) and Digital Elevation Model (DEM) images, as well as magnetic data, were used to study the geological features of Kuh-e-Djahan Bin in Iran. Scanned geological map which was geometrically corrected was then used with TM and DEM images to extract geological information. Several analyses have been done to the images such as colour composite, principal component analysis, ratio and supervised classification. In order to evaluate the classification process, accuracy assessment was done to the classified images. The accuracy statistics was the measuring scale of the classification. In addition, contour and drainage patterns analyses were also done to extract elevation, flow direction and flow accumulation data to provide further information. Magnetic modelling with a small degree of unsuitability (misfit) between the model and the geological data was employed in order to compensate the subsurface interpretation. In a nutshell, these few named analyses were flawlessly facilitated in interpreting lithologic and structural geological features which was the interest of this study.
-
-
-
Seismic Attributes for Reservoir Property Prediction - A Review
Authors Muhammad Sajid and Zuhar Zahir Bin Tuan HarithSeismic attributes are extensively used in prediction of reservoir property, such as morphology Properties and petrophysical properties of the reservoir. There is no direct relation exist between most of the calculated attributes and the measured reservoir property but still we can use these seismic attributes by statistically correlating them with the measured reservoir property at the well location. In this paper we will review the correlation of some of the important properties of the reservoir with the seismic attributes and how these attribute should be used to predict the reservoir desired property of investigation. We will describe how to select the different attributes to produce a meta-attribute (hybrid attribute) and how to use THESE META-ATTRIBUTES to map the reservoir property. We will discuss how other branches of geophysics (AVO, Rock-Physics) help us in more reliable reservoir property prediction.
-
-
-
A Low Frequency Seismic Survey in an Exploration Environment
Spectraseis and PETRONAS acquired a low frequency (LF) passive seismic survey over a producing field and a series of leads and prospects in south-Asia. Efficient field operations and close coordination among all involved parties provided a good quality dataset with minimal environmental impact and HSE exposure in only 9 days of recording. Despite the presence of high levels of noise from exploitation activities and interference from a strong near surface effect, detailed analysis and careful processing returned results that are reliable and consistent. The LF results show a good correlation to well results, with both productive and dry areas correctly identified. The survey also extended over undrilled prospects. Good quality results over the known areas extends the usefulness of the survey, adding information to the body of geophysical and geological knowledge for ranking further exploration and appraisal prospects in the area.
-
-
-
3D Coil Shooting Survey on Tulip Field: Data Processing Overview – Planning, Challenges and Opportunities
The Tulip 3D survey is a single-vessel Coil Shooting project east of Kalimantan, offshore Indonesia. The coil geometry is very different to the conventional race-track towed streamer approach. Whilst it results in many acquisition and imaging benefits, the circular geometry introduces several differences, a number of new challenges and opportunities in data processing. A fit for purpose processing workflow was tailored to address the challenges, and at the same time taking advantage of the opportunities provided by the circular geometry. The Tulip survey area is geophysically very complex due to the presence of several unfavourable geological factors, especially in the near surface. In particular the rough sea bottom and very bright Bottom Simulating Reflectors (BSR) below the seabed generate several orders of multiples and degrade the subsurface illumination. The presence of free gas below the BSR causes a sudden frequency and amplitude decay of primary reflections. Complex subsurface geology further complicates the scenario. All these conditions when combined result in very strong and high orders of surface multiple reflections, diffracted multiples, absorption, scattering and poor transmission of seismic signal energy. The consequences of these complexities is overall poor seismic response, very low acoustic impedance contrast at the reservoir level and therefore extremely 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 for the appraisal campaign, eni successfully acquired a Coil shooting (French, Cole, 1984; Durrani et al, 1987) survey on the Tulip discovery. The acquired data was processed through to depth imaging utilizing multiazimuth tomography velocity model building. 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. Prior to the commencement of the acquisition, a subset volume of 3D synthetic data with coil geometry was generated to assess the application of 3D processing algorithms. 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 were 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.
The second aspect and very different to the conventional processing is related to the spatial sampling, with the Coil shooting geometry, the trace offset distances are not regularly spaced in the shot or midpoint domain. This result in the midpoint/offset clustering inside the circles and inducing some apparent geometrical or moveout distortion in the seismic reflections, which makes the application of conventional straight sail line based processing methods unsuitable. The third and perhaps the main
challenge related to the Tulip's geometry is the although very high, but irregular fold of coverage, resulting in amplitude footprints, which change position as a function of the incidence angle, and require proper treatment in order to avoid amplitude inconsistencies and migration artifacts. On the advantages and opportunities aspects, the circular geometry allows the full 3D processing algorithms to work at their best. The true-azimuth 3D demultiple tools work very well for the Tulip survey. The same conclusion is valid for velocity model building and migration algorithms due to the large azimuthal content. This paper will discuss some of the pre-emptive measures taken during the survey design stage prior to both acquisition and processing as well as the overview of the processing experience of the Tulip project and some relevant results.
-