Seismic Attributes Analysis as a Precursor for Hydrocarbon Indication: A Case Study of Onshore Fuba field, Niger Delta, Nigeria (original) (raw)
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2019
This research work is aimed at using acoustic impedance as means of predicting lithology and hydrocarbon away from well control of “Ovi” Field hence providing a detailed evaluation of the hydrocarbon potential of the area. The methodology used involves identification of hydrocarbon bearing reservoirs from well logs using Gamma ray and resistivity logs, wells correlation, petrophysical analysis, well to seismic tie, horizon and fault mapping, generation of structural maps, acoustic impedance crossplot analysis and seismic inversion using model based approach. Three reservoir sand were mapped within the Agbada Formation. From the crossplot of acoustic impedance against gamma ray, porosity and water saturation, the acoustic impedance ranges from 24500-27500 (ft/s)*(g/cc) for shale and 17500-24500 (ft/s)*(g/cc) for sand based on the saturating fluids, the results also shows that acoustic impedance have a linear relationship with water saturation, while porosity have an inverse relations...
2021
Seismic data volume was employed to gain more insights into the complexities of the hydrocarbon hosting units within and outside the vicinity of well control in the OK-field Niger Delta to overcome wrong deductions from complexly faulted subsurface configuration for the oilfield exploration programme. The methodology involved integration of well log with seismic data, seismic structural analysis and seismic attributes analysis. Horizons and fault interpretations were carried out to produce subsurface attribute maps. Lithologic panels derived from well log data showed that the study area is characterized by sand-shale interbedding. Two hydrocarbon bearing reservoirs were delineated within the study interval, namely: R1 and R2. Well to seismic tie revealed that these horizons tied direct hydrocarbon indicators (bright spots) on the vertical sections. Structural interpretation revealed that “OK” field is characterized by a rollover anticline, with a closed trapping mechanism for the D ...
Journal of Petroleum Exploration and Production Technology, 2019
Structural interpretation and inversion analysis were used to characterize hard-to-image reservoirs, to predict subsurface interwell reservoir properties for optimum reservoir heterogeneity description, and to fine-tune drilling locations in 'DJ' Field, Niger Delta. Post-stacked 3D seismic data, composite well logs, and velocity checkshot data were used for the reservoir analysis. The study entailed mapping of structural framework, horizon picking, wavelet extraction, log editing and correlation, building of low-frequency model, acoustic impedance inversion and crossplot analysis of reservoir properties. Four major antithetic, three regional, and five minor faults were identified. The inversion results revealed an acoustic impedance range of 9700-25,000 ft/s g/cc and porosity range of 25-45% within the hydrocarbon-bearing sands. Crossplot analysis of Poisson and Vp/Vs ratio against acoustic impedance revealed Poisson ratio range of 0.30-0.45 and V p /V s ratio range of 1.3-2.50 within the delineated hydrocarbon-bearing sandstone interval. The overall correlation coefficient between the inverted and actual impedance was about 98% across the eight wells. Acoustic impedance slice at 2300 ms revealed low acoustic impedance sand within the range of 13,000-24,000 ft/s g/cc at the western and central part of the field. Comparing the acoustic impedance slice and seismic attribute maps at the target reservoir zones revealed high reflection amplitudes (bright Spots), indicative of hydrocarbon accumulation. The study predicts new and reliable drillable locations, by lithologic/fluid discrimination in the analysis of delineated reservoirs in the study area.
Asian Journal of Basic Science & Resea, 2023
Application of 3-D seismic attributes analysis for hydrocarbon prospectivity in the onshore Fuba Field, Niger Delta, Nigeria using Well-logs and 3D Seismic data are here presented. Well-to-seismic ties, faults and horizon mapping, time-surface generation, depth conversion and seismic attributes generation were carried out using Petrel software. The structural interpretation of seismic data reveal highly synthetic and antithetic faults which are in line with faults trends identified in the Niger Delta. Of the 36 interpreted faults, only synthetic and antithetic faults are regional, running from the top to bottom across the field. These faults play significant roles in trap formation at the upper, middle and lower sections of the field. Three distinct horizons were mapped. Reservoir M is found at a shallower depth from 10937 to 10997 ft, reservoir N is found at a depth ranging from 11213 to 11241 ft while reservoir O is found at a deeper depth ranging from 11681 to 11871 ft respectively. Analysis of the relevant seismic attributes such as variance edge, root mean square, maximum amplitude, average magnitude and maximum magnitude were applied to the seismic data. The variance values ranges from 0.0 to 1.0. The Variance edge analysis was used to delineate the prominent and subtle faults in the area. The RMS amplitude values ranges from 9,000 to 13,000 in the reservoirs. The root mean square amplitude, maximum amplitude, average magnitude and maximum magnitude analysis reveal bright spot anomaly. These amplitude anomalies served as direct hydrocarbon indicators (DHIs), unravelling the presence and possible hydrocarbon prospective zones. Results from this study have shown that away from the currently producing zone of the field, additional leads and prospects exist, which could be further evaluated for hydrocarbon production.
Authorea (Authorea), 2023
Seismic stratigraphic and structural interpretation is often hampered by seismic resolution and, sometimes, human's inability to identify a subtle feature on the seismic. These factors have frequently led to the poor seismic interpretation of geologic features. Thus, an integral approach to studying the structural patterns and hydrocarbon bearing zones using seismic attributes were carried out on the Tomboy field using 3D seismic data covering approximately 56 km 2 of the western belt of the Niger Delta. The seismic volume underwent post-stack processing, which enhanced seismic discontinuities. A deep steering volume was first created, and several dip filters were applied to enhance faults in the study area. After that, curvature and similarity attributes were calculated on the dip-steered and fault-enhanced volume. These calculations show detailed geometry of the faults and zones of subtle lineaments. Six faults (F1, F2, F3, F4, F5, and F6) were identified and mapped. These faults range from antithetic to crestal growth faults. Two major growth faults (F5 and F6) were revealed to dip in the NE-SW directions. A near-extensive crestal fault (F4) appeared beneath the major faults. Although several minor fractures were displayed in the southern and central portion of the seismic data, the SW dipping crestal fault (F4) and growth fault F6 are responsible for holding the hydrocarbon found within the identified closures. Using attributes on the seismic data increased confidence in the mapping and interpreting structural features. Furthermore, Energy attributes were used as Direct Hydrocarbon Indicator (DHI) to visualize viable areas within the study and permits a more robust interpretation. Time slices were taken at regions of flat and bright spots. Spectral decomposition attribute was run on these slices to display areas of high amplitude reflection typical of hydrocarbon-bearing regions, which are trapped mainly by regional to sub-regional growth faults. The surface attribute calculated on the generated surface shows that the field is dominantly controlled by faults serving as traps for hydrocarbon.
Journal of Environment and Earth Science, 2019
Seismic facies analysis is a key component of Seismic interpretation workflow, as much information on depositional process, environment, reservoir architecture and potential can be determined from the seismic data. This enhances the seismic visibility of subtle stratigraphic features, and prediction of new prospects for drilling due to lateral continuity of sand bodies (the hydrocarbon reservoir) deposited within the sedimentary column. This study presents the results of the application of seismic amplitude inversion and spectral decomposition to differentiate lithofacies within a thin-sand reservoir and show their lateral and vertical continuity using amplitudederived attributes (rock properties) in the interpretation of 3D seismic and well log data from "TOMBOY" field Niger Delta. A thin-sand reservoir was delineated from lithologic log signatures within the interval 11,135.61-11,210.35ft which corresponds to the time window 2.752-2.768secs on the seismic data along an arbitrary line drawn to connect the six wells (01-06) in the field. Crossplot of acoustic impedance against density across the reservoir bed showed three compartments interpreted as gas filled sand, oil filled sand and shale. The interpretation was enhanced via spectral analysis by computing frequency maps of acoustic impedance, density and velocity using discrete Fourier transform (DFT) technique at top (2.752sec) of the reservoir in terms of magnitude, phase and frequency. Phase response for the three attributes (acoustic impedance, density and velocity) showed lateral continuity and discontinuity of sand lithofacies at the various well locations which were not evident on their original amplitude time slice, while frequency response showed bed thickness, with low frequency indicating presence of hydrocarbon or sand rich beddings, while high frequency indicates thin shale beddings. It was observed that the top (2.752sec) of the reservoir for wells 02, 05, 01 and 04 showed low frequency values for the three attributes (acoustic impedance, density and velocity) which indicates potential zones for hydrocarbon production and development in the field, while wells 03 and 06 within the same time slice (2.752sec) showed a higher value in acoustic impedance frequency, density frequency and velocity frequency and suggests the presence of thin shale facies at the top (2.752sec) of the thin-sand reservoir. By defining the lateral and vertical continuity of sand facies within the reservoir bed, hydrocarbon fairways were better defined and knowledge of this can be incorporated into drilling decisions for field development. The results gave enhanced structural disposition of the reservoir bed and more insights into the variation of sand lithofacies with depth.
Identification of seismic attributes for hydrocarbon prospecting of Akos field, Niger Delta, Nigeria
SN Applied Sciences, 2020
In this study, we have extracted and analyzed four seismic attributes of Akos oil field to obtain more information about the structures, stratigraphy and hydrocarbon potential of the Akos field from available seismic and a suite of well logs data. Two lithology and reservoirs were delineated from the well logs. Two horizons and growth faults were identified in the seismic sections. For a comprehensive analysis of the structural and stratigraphic understanding of the reservoirs, four seismic attributes variance edge, sweetness, root mean square and relative acoustic impedance were applied to the seismic data. The Variance edge analysis was used to delineate the prominent and subtle faults in the area. The high sweetness regions in the seismic data indicate high amplitude which indicates the presence of hydrocarbon-bearing sand units. The root mean square amplitude analysis also indicates the presence of hydrocarbon in seismic data. The relative acoustic impedance analysis was used for delineating lithology variation in the seismic sections. The result of the seismic attribute analysis has shown that the Akos field has good hydrocarbon prospects.
SN Applied Sciences, 2020
The task of minimizing pitfall in quantitative reservoir assessment and evaluation is an integral aspect of any promising petroleum exploration and evaluation project. The Niger Delta oil province in Nigeria is chiefly composed of several pay zones with many stratigraphic intervals of sand and shale formations in varying proportion. Whereas conventional seismic interpretation technique poses certain degree of uncertainty in reservoir characterization, seismic inversion constraint by log data brings significant improvement in interpretation that reduces uncertainty in the delineation of reservoir characteristics, volume and distribution. In this present study, post-stack seismic inversion and seismic attributes analysis were used to evaluate the potentials and prospects of mapped reservoirs in a field, offshore depobelt, Niger Delta. The implementation of the tasks consists of mapping of structural framework, horizon picking, log editing and correlation, wavelet extraction, building of low-frequency model, acoustic impedance inversion and crossplot analysis of reservoir properties and attributes. A hybrid approach (formulated using Greenberg-Castagna equation) specific for the Niger Delta depobelts was used to estimate and generate shear wave velocity for the wells. Results obtained from inversion depict an acoustic impedance values in the range 150-280 ft/s g/cc and V P ∕V S of 1.25-2.50 at a depth range of 9250-9280 ft within the hydrocarbon-bearing sands in the two wells. Region of low acoustic impedance (representing high reservoir porosity) coupled with a corresponding low V P ∕V S ratio (indicating hydrocarbon accumulation) is presumed to have high prospects for exploration and well development. Altogether the degree of correlation between the inverted and actual impedance was found to be about 90% across the wells. It is evident that the acoustic impedance slice at 3000 ms depicts low acoustic impedance sand within 18,500-20,000 ft/s g/cc at the northeastern and southeastern regions of the field. High reflection amplitudes (bright spots) signifying hydrocarbon accumulation are also revealed on seismic attribute maps with surrounding shale diaper as the source rock. This study has revealed the prospect (i.e., existence of active petroleum system of probable economic value) of the delineated field in the Niger Delta depobelt.
Journal of Applied Sciences and Environmental Management, 2019
This study presents the result of a Model-based seismic inversion technique which was used to invert an acoustic impedance structure within a reservoir interval by intergrating well logs and 3D post stack seismic data obtained from XY field offshore Niger Delta. The purpose was to delineate lateral and vertical alternations in subsurface rock properties which is caused by difference in lithofacies within the reservoir interval. This would help to define hydrocarbon fairways better and constrain the range of hydrocarbon zones for field development. The inversion workflow used in this study includes forward modelling of reflection coefficients from a low frequency impedance model driven from well logs and convolution of the reflection coeffiecients with a source wavelet derived from the seismic data. Acoustic impedance cross section obtained from the inversioin algorithim showed impedance values increasing from 4112 to 7539 (m/sec*g/cm 3) from top to bottom of the reservoir with gas filled sand facies observed at the top of the reservoir within time window 1900-2100msec. Below time window 2100msec, there is variation in impedance values observed within the anticlinal structures seen at this interval which suggests porous sand facies containing little shale intercalations. This is characteristic of sandstone reservoirs within the Agbada formation in the Niger Delta. These sands were most likely deposited through distributaries channel deposits, distributaries mouth bars, barrier bars, alluvial fans and crevasse which characterize the reservoir rocks (sandstones) in the Niger Delta. At time window 2100-2200msec, anticlinal structures containing porous sand facies with little shale intercalations was observed again. At time window 2200msec, water bearing sand facies (clean sandstone) was observed and at the bottom of the reservoir within time window 2300-2500msec, the impedance was dominantly high which suggests the presence of shale facies at the bottom of the reservoir. Gas-oil contact (GOC) was observed between time window 2100-2200msec of the acoustic impedance section. These variations in acoustic impedance amplitude is due to lateral changes in lithofacies within the reservoir. The results obtained gave enhanced structural disposition of the reservoir and are important for accurate stratigraphic imaging interpretation to lower the risk in drilling of exploratory and development wells.
Seismic Attribute Analysis for Prospect Delineation in ‘TMB’ Field, Niger Delta Basin, Nigeria
Journal of Applied Sciences and Environmental Management
The ‘TMB’ Field was evaluated to detect hydrocarbon prospects for the purpose of increasing production volume using seismic attribute analyses. A total of eight sand tops were correlated across the Wells and faults orientation with significant displacement were picked across the field. Three horizons (Res. E, Res. H and Res. J) were used to generate the time maps which were converted to depths by a polynomial function from Time-Depth relationship. Two of the faults are major syn-tectonic growth faults that divides the field into three Fault Blocks (FB1, FB2 and FB3). Seismic attributes (Average Energy, Root Mean Square (RMS), Sweetness and Relative Acoustic Impedance (RAI)) amplitudes were examined to identify hydrocarbon prospect in the reservoirs. An area of interest (prospect) in one of the Fault Blocks (FB3) revealed attribute amplitude responses that suggest the presence of hydrocarbon was identified. The extracted attribute from Average energy, RMS and Sweetness attributes sho...