Reservoir Characterization, Modelling and Lateral Predictions Using Multivariate Analysis: A Case Study of Hems Field, Bohai Bay, Liaohe Field, China

Qualitative and quantitative predictions of reservoir properties and geometries beyond well control are vital to understanding the intrinsic characteristics of subsurface formations. Using well log data, 3D Seismic data, Geostatistical simulations, reservoir characterization, modeling via multivariate analysis was carried out for and lateral predictions on data set obtained from Liaohe field, western sag, Bohai Bay, Northern China. This sag is an intra-cratonic basin of Archean to Recent age. Stratigraphic analysis, structural analysis, geomodel building and geostatistical methods were used. Well logs methods include conventional interpretation by picking sand units based on Self potential log (SP) and Resistivity logs (LLD) in addition to computation of volume of shale and other petrophysical properties. Unavailable logs like Density and Neutron were predicted from a cored well whilst missing logs sections were predicted using neural networks and fuzzy logic. Clustering technique was employed to predict facies (electrofacies) occurrences based on various log types. Sand tops earlier picked from well logs were laterally traced on seismic sections after well to seismic tie. Structural interpretation was done to map the architectural pattern of the rock units. The post-stack seismic inversion was done and calibrated with logs from 12 wells producing acoustic impedance and elastic impedance volumes. Multi-attribute analysis was used to predict rock properties like porosity from inversion results and vintage seismic data. Modeling of variogram and structural elements was done, after which suitable geostatistical simulation algorithms were used to populate cells and realize multiple equiprobable rock properties for the zone of interest after upscaling all needed rock properties into the earlier built non-partitioned simulation case. These were achieved using standard software such as Petrel®2008, CGGVeritas™ Hampson Russell suite (2008), Interactive Petrophysics v3.5, Kingdom Suite (SMT) 2008, GeoGraphix® 2008 and Surfer 9 (Golden Software). Results show that clustering models converged to 2 classes namely sand and shale. Sand and shale sequences are fairly mixed and vertically inconsistent as a result of rapid deposition amidst unconsolidation on the toe of the sag structure. Petrophysical values viz hydrocarbon saturation is above 70%, porosity between 0.1 and 0.4, permeability between 0.6 and 3.0mD and volume of shale between 0.3 and 0.8. Structurally, 35 major and minor faults were mapped with 15 used for modeling. Prevailing fault orientation is northeast/southwest, dipping south-easterly and trending northwest-southeast direction. Bedforms are complex with gradual lateral changes in lithofacies. Sharp boundaries in horizontal direction define different depositional facies with a flexible non-partitioned model adopted. The lithofacies model result showed continuous lithological units with inconsistencies of stratigraphic and structural truncations which were also replicated on the rock properties model with clear heterogeneity seen in the observed values. Horizon cubes produced in regions of interest defined relationships that are clearly correlative with rock properties than with seismic attributes/properties. Majority, some of the properties predicted from multiattribute analysis of seismic data calibrated with computed logs correlated well with the simulated rock property volumes. In conclusion, successful prediction has been done for rock properties at inter-well points and locations beyond well control. The heavy hydrocarbon in reservoir units of the field can be recovered by steam injection method (SAGD). The methodology and interpretation approach adopted in this work can be implemented initially with very few wells for multiattribute volume prediction, seismic inversion and on a larger scale with more wells for geostatistical simulations and modeling

Sequence stratigraphy study within a chronostratigraphic framework of ‘Ningning field’, Niger Delta

Sequence stratigraphy model developed for the Ningning field is based on the interpretation carried out on the different wells that penetrated the various subsurface lithologies. Basically three depositional sequences were delineated from the five wells studied. The Vail model used made out a third and forth order stratigraphic surfaces that all fall within the central swamp depobelt of the Basin. The five wells used show the presentation of the interpretation and the models. All the sequence tracts were appropriately represented starting from the Lowstand Transgressive and Highstand system tracts, except in well 005 where the Lowstand of the second sequence was missing. This is achieved by incorporating signature motifs from wireline logs coupled with biostratigraphy data and inferred paleobathymetry. This has revealed the field-wide reconstruction of a chronostratigraphically constrained biostratigraphy of subsurface lithological sequences with limited informatio

Seismic Stratigraphic Analysis Fordepositional Environment and Hydrocarbon Occurrence Appraisal using Attributes

Seismic stratigraphical interpretation of rock deposits has been done using migrated 3D seismic data in SEGY format. This has taken into consideration the analysis of both seismic sequences and seismic facies within the hydrocarbon reservoir of the Dongian oil block, North-east China. Methods adopted include that which identifies contacts of the upper and lower boundaries of the depositional sequences that were not absolutely correlatable. The style of the reflection patterns is discovered to be borne out of the very chaotic and dipping basement rocks. This is responsible for the arrangements of the overlying sequences which were continuous or truncated either on the basement or by the gently dipping listric fault amidst the middle portion of the sequences. In all two unconformities were observed. It was discovered that sequence 1 is the prolific reservoir and the overlying sequence 2 characterized by the sub-parallel to sigmoidal internal reflection pattern is a combination of reservoir and the seal that impedes hydrocarbon migration and makes the trapping system effectiv

RESERVOIR CHARACTERISATION AND STRUCTURAL INTERPRETATION FOR PROSPECT EVALUATION- A CASE STUDY

This paper presents a case study dealing with reservoir delineation and characterisation of the Basecopia field, part of Niger Delta Nigeria. The data set utilized for this work incorporate 3D seismic data, well log suites containing gamma rays, resistivity and porosity logs (neutron and density). These logs were utilized to focus petro-physical properties in three (3) wells. 780 inlines and 496 crosslines of seismic information covering an area of about 234 km2 were utilized. Faults were picked and correlated. Horizons of hydrocarbon bearing sands were picked in view of the re-suit from seismic- to-well tie. These were utilized to produce time and depth maps for a horizon keeping in mind the end goal to recognize the different basic highlights inside the field. Petro-physical aftereffects of the study demonstrate the dominating liquid found in the three wells is light oil at True Vertical Depth Sub Surface (TVDSS) of -7109 to -7333 ft. in Well A, -6916 to -7044 ft. in Well B and -7694 to -7858 ft. in Well C. Thereafter, seismic attributes such as the instantaneous frequency and the dominant frequency indicated the presence of channel filled sand containing hydrocarbon in regions around the wells. Hence, the wells can be said to be properly situated within the reservoir hydrocarbon bearing sand with spatial facies evenly distributed. The study however concluded that Well A bears a considerable amount of reserves of about 209.52Mbbl

2- D Electrical Imaging And Its Application In Groundwater Exploration In Part Of Kubanni River Basin-Zaria, Nigeria

A modern field system, Terrameter (Signal Averaging System) SAS 4000/1000, was used to accomplish the task of exploring groundwater in Kubanni River Basin. 23 image lines were measured at different strategic locations of the study area based on the fractured map of the area and previous information obtained from the area. Four straight line profiles with a spread of 200 m per section were traversed during the course of this survey with three of them generally trending along a North-South direction while the fourth, trends approximately along the East- West direction. The four profiles have a total coverage distance of about 4.2 km. The data used for this survey was acquired by measuring a series of constant traverse along the same line but with the electrode spacing being increased with each successive traverse. Since increasing separation leads to greater depth penetration, the measured apparent resistivities was used to construct a vertical contoured section displaying the variation of resistivity both laterally and vertically over the section. Interpretation of the data acquired using this equipment revealed the suitability of the Southern part of the study area for location of boreholes, as the resistivity values of rock obtained around this zone reflects aquiferous materials. More layers of rock units around Area BZ and Tudun Sarki were revealed than what was reported by previous workers. Also observed were slight variation in depth to bed rock around area BZ and the Nigerian College of Aviation Technology as compared with observations made by previous workers. However, the observation of the increasing undulating bedrock geometry with depth towards the southern part of the study area was consistent with that of the previous workers

Evaluation of Shale Effect on Saturation Exponent from Well Logs in an Offshore Field, Niger Delta.

Hydrocarbon recovery is subject to various elements set to validate not only the availability of the type of fluid present at the subsurface, but also how saturated is the host rock with the fluid. A study on saturation was carried out on the hydrocarbon locked in reservoirs of the N-1 and D-1 wells. The water saturations were determined using various saturation equations by various authors from literatures. This evaluation led to the determination of the permeability of the reservoirs through the Timur equation and the values were within the range 222.8mD-2518.5mD in well N-1 and 434.4mD-2534.3mD in well D-1. The 7 pay zones of both wells showed a high correlation based on the petrophysical parameters which could be the basis of a conclusion of lateral continuity across the reservoir although the formations interpreted are characterized by clay fingering. An analysis carried out for the determination of the permissible range of the saturation exponent ‘n’ used and assumed as 2 which agrees with that in the basic Archie equation, but for the BOD-1b zone of D-1 with both values 1 and 2 perfectly matching

Reservoir characterization and modeling of lateral heterogeneity using multivariate analysis

Reservoir characterization deals with the description of the reservoir in detail for rock and fluid properties within a zone of interest. The scope of this study is to model lateral continuity of lithofacies and characterize reservoir rock properties using geostatistical approach on multiple data sets obtained from a structural depression in the bight of Bohai basin, China. Analytical methods used include basic log analysis with normalization. Alternating deflections observed on spontaneous potential (SP) log and resistivity log served as the basis for delineating reservoir sand units and later tied to seismic data. Computation of variogram was done on the generated petrophysical logs prior to adopting suitable simulation algorithms for the data types. Sequential indicator simulation (SIS) was used for facies modeling while sequential gaussian simulation (SGS) was adopted for the continuous logs. The geomodel built with faults and stratigraphical attitude gave unique result for the depositional environment studied. Heterogeneity was observed within the zone both in the faulted and unfaulted area. Reservoir rock properties observed follows the interfingering pattern of rock units and is either truncated by structural discontinuities or naturally pinches out. Petrophysical property models successfully accounted for lithofacies distribution. Porosity volume computed against SP volume resulted in Net to gross volume while Impedance volume results gave credibility to the earlier defined locations of lithofacies (sand and shale) characterized by porosity and permeability. Use of multiple variables in modeling lithofacies and characterizing reservoir units for rock properties has been revisited with success using hydrocarbon exploration data. An integrated approach to subsurface lithological units and hydrocarbon potential assessment has been given priority using stochastic means of laterally populating rock column with properties. This method finds application in production assessment and predicting rock properties with scale disparity during hydrocarbon exploration

Applications of 3-D Structural Interpretation and Seismic Attribute Analysis to Hydrocarbon Prospecting Over X – Field, Niger-Delta

Complexly faulted subsurface configuration is capable of causing erroneous deductions in the absence of a well packaged interpretation approach and workflow for an oilfield exploration programme, thus a well prepared analysis saddled on the use and integration of sufficient data is indispensable to the unravelling of complex field subsurface structure as the search for oil and gas progresses into deeper waters. Suite of signatures from wireline logs and seismic volume was employed to gain more insight into the complexities of the hydrocarbon hosting units within and outside the vicinity of well control in the X-field Niger Delta. Horizons and fault interpretation were carried out to produce subsurface structure maps. Amplitudes of the horizons mapped were extracted and were used to study the distribution of the hydrocarbon sand. Three hydrocarbon bearing reservoirs were delineated within the study interval, namely: ROJ A, ROJ C and ROJ D. Well to seismic tie revealed that these reservoirs tied direct hydrocarbon indicators (bright spots) on the vertical sections. The structure maps produced revealed a series of NW-SE and E-W trending growth faults and fault echelons, most of which dip to the south. Fault assisted closures were revealed at the southern part of the field, which correspond to the crest of roll over structures and possibly served as the trapping mechanism for the reservoirs. The reflection amplitude of the studied horizons shows a fine network of anomalies that can be correlated to the prediction of the lateral distribution of the hydrocarbon sand. The conclusion of the study was that the western part of horizon ROJ A is a highly prospective area as bright spots were observed in the region. Also in the adjacent southern direction of this horizon, hydrocarbon accumulations have been confirmed from wells. These gas sands are possibly trapped in anticlinal closures located in the same area. On the other hand, the results from the study of horizon ROJ C suggest development opportunities in the southern area. High amplitude gas sands are seen to spread to the south and stratigraphy was assumed to play a major role in hydrocarbon migration. The study over horizon ROJ D reveal likely geologic features like regional sand pinch outs and channels in the southern part of the field. Spectral decomposition interpretation was suggested to be used further in improving the delineation of the thin reservoir sand bodies and for better outlining of their geometries but was not available on the workstation used The study has shown the feasibility of integrating structural interpretation and instantaneous amplitude in prospect identification and reservoir prediction

Groundwater Prospecting Using Electrical Resistivity Profiles Over Jubilee Homes Parkland, Southwest, Nigeria

Urbanization is speedily catching on erstwhile fallow hinterland area of southwest Nigeria. Due to the various production companies springing up in the location adjoining area are experiencing influx of citizenry and accommodation and sustenance become a predominant challenge. Portable water is critical to the survival of man, hence the reason for this study. Electrical resistivity survey were carried out at Jubilee Homes Parkland, to delineate subsurface layers and determine the ground water potential, so as to make adequate provision of portable water supply for the settlements springing up within this area. The electrical resistivity method adopted for this study employed the use of ABEM SAS 1000 terrameter which worked on 16 vertical electrical sounding (VES) points within the area. A maximum distance of 550m current electrode (AB) spread was adopted for this purpose. The result shows the presence of four geoelectric layers with the resistivity of the first layer ranging from 25.54Ωm-619.45Ωm and thickness of 0.14-9.21m representing topsoil. The second geoelectric layer has a resistivity ranging from 20.94Ωm-706.82Ωm and thickness of 2.58-35.36m representing laterite, while the third geoelectric layer has a resistivity ranging from 12.29Ωm-598.93Ωm and thickness 3.33-58.06m representing sandy clay. Finally, the fourth geoelectric layer has a resistivity ranging from 12.10Ωm-1980.52Ωm and thickness of 11.4-45m representing sand. It can be concluded that the fourth layer is most prolific and attractive to be explored for groundwater. This thereby affords residents and potential settlers in the area a considerable confidence level in accessing sufficient groundwater for their various uses. Furthermore, construction purposes ongoing in the location could make use of this evaluation to satisfy their need of locating water for their operation

The geochemistry and geotechnical (compaction) analysis of lateritic soils: A case study of Okpanam area.

The major elements of geochemistry and compaction characteristics of lateritic soils in Okpanam area, located in the Anambra Basin were investigated. This was with a view to determine the silica sesquioxide ratio and assess the suitability of the lateritic soils as a highway sub-base and sub-grade materials. Bulk samples of soil were collected from two separate horizons – A and B at depths of 1.38m and 3.39m in a burrow pit. The major elements geochemical analysis was carried out by means of Atomic Absorption Spectrometry (AAS). The geotechnical analysis – compaction, was executed by following the modified AASHTO test (T-180). The amount of total irons in terms of iron III oxide ranged from 6.07% - 7.22%. Silica – sesquioxide of iron and aluminium molar ratios were between 1.9 and 1.96. Compaction characteristics values for this area varied with sampling depth, with an average Optimum Moisture Content (OMC) range of 11.10% to 9.30% and an average Maximum Dry Density (MDD) range of 2.00g/cm3 to 2.06g/cm3. With these values, the soils can be compacted at specific optimum moisture contents in order to ensureclose packing of the soil particles under compaction energy, thus ensuring their subsequent use as sub-base and sub-grade highway construction materials