Petrophysical Properties Estimation of Euphrates Reservoir in Qayyarah Oil Field Using Core and Well Log Data

The Early Miocene Euphrates Formation is characterized by its oil importance in the Qayyarah oil field and its neighboring fields. This study relied on the core and log data analyses of two wells in the Qayyarah oil field. According to the cross-plot’s information, the Euphrates Formation is mainly composed of dolomite with varying proportions of limestone and shale. Various measurements to calculate the porosity, permeability, and water saturation on the core samples were made at different depths in the two studied wells Qy-54 and Qy-55. A relationship between water saturation and capillary pressure has been plotted for some core samples to predict sites of normal compaction in the formation. The line regression for this relationship was considered as a function of the ratio of large voids to the total volume of voids in the sample. The coefficient of determination parameter was used in estimating the amount of homogeneity in the sizes of the voids, as it was observed to increase significantly at the sites of shale. After dividing the formation into several zones, the well log data were analyzed to predict the locations of oil presence in both wells. The significance of the negative secondary porosity in detecting the hydrocarbon sites in the Euphrates Formation was deduced by its correspondence with the large increase in the true resistivity values in both wells. More than 90% of the formation parts represent reservoir rocks in both wells, but only about 75% of them are oil reservoirs in the well Qy-54 and nearly 50% of them are oil reservoirs in the well Qy-55.

Electrofacies as a Tool for the Prediction of True Resistivity Using Advanced Statistical Methods—Case Study

Statistical analysis methods have been widely used in all industries. In well logs analyses, they have been used from the very beginning to predict petrophysical parameters such as permeability and porosity or to generate synthetic curves such as density or sonic logs. Initially, logs were generated as simple functions of other measurements. Then, as a result of the popularisation of algorithms such as the k-nearest neighbours (k-NN) or artificial neural networks (ANN), logs were created based on other logs. In this study, various industry and general scientific programmes were used for statistical data analysis, treating the well logs data as individual data sets, obtaining very convergent results. The methods developed for processing well logs data, such as Multi-Resolution Graph-Based Clustering (MRGBC), as well as algorithms commonly used in statistical analysis such as Kohonen self-organising maps (SOM), k-NN, and ANN were applied. The use of the aforementioned statis-tical methods allows for the electrofacies determination and prediction of an Rt log based on the other recorded well logs. Correct determination of Rt in resistivity measurements made with the Dual Laterolog tool in the conditions of the Groningen effect is often problematic. The applied calculation methods allow for the correct estimation of Rt in the tested well.

The behaviour of six electrode arrays used in electrical resistivity imaging to detect underground cavities: a numerical study

The aim of this work is to evaluate the efficiency of six electrode arrays used in electrical resistivity imaging. Pole-Pole (PP), Pole-Dipole (PD), Wenner-Alpha (WA), Wenner-Schlumberger (WS), Dipole-Dipole (DD) and multiple Gradient (MG) electrode arrays have been selected to detect underground cavities at shallow depth. Numerical simulation has been made for three synthetic models that have been generated using Res2dmod program. Each model represents three cavities with 2m diameter, spaced 6m from each other and located at a depth of 1.5m from the surface of the ground: 1) air-filled cavity, 2) half-watered cavity and 3) full-watered cavity. The background resistivity of each model was chosen equal to 10, 50 and 250 Ωm respectively. The resistivity of the air and water were set at 106 Ωm and 1 Ωm respectively. The results show that the PD, MG, PP and WS arrays gave good resolutions and clear images, and are less contaminated by noise. The DD array is very sensitive to noise and for this reason, it gave less accurate results for the first and the second synthetic models. An exception is the third synthetic model, where a good resolution model was obtained. This means, that the DD is more efficient in mapping cavities when the background environment is moderately resistive. The shapes of resistive air-filled cavities were found more clearly than those of conductive watered cavities, for the latter, however, the true resistivity values were better estimated than for the air-filled cavities. From the results of the analysis of the inverted synthetic models, the PD, MG, PP and WS arrays show the best results among the other used electrical arrays.

A 3-D geoelectric model over mineralized zone of Ugonoba, Edo State, Nigeria

The occurrence of solid minerals in Ugonoba community was investigated using the 3D electrical resistivity method. Data was acquired using PASI 16GL Terrameter using the wenner electrode configuration with a view to delineating mineral deposits in the study area. During the reconnaissance survey, the outlook of some geological features in the form of outcrops on the surface formed part of the motivation for the geophysical survey within the Ugonoba area. Ten traverses of 200 m maximum spread and 10m electrode spacing with total depth of 40.07 m were obtained in the study area to form a square grid. The acquired data was first processed and inverted using RES2DINV software to generate ten 2-D model images and later collated into 3-D using the inversion code of RES3DINV software which automatically determines a horizontal 3D depth slice, cubes and block models of resistivity distribution. These models generated were interpreted and used to ascertain the true resistivity, lithologic formation, depth extent to any buried mineral and aggregate deposited in the study area. The extracted 3D model images revealed evidence of some geological materials/minerals in the study area which fall within the high resistivity range of 2500 Ωm to 14376 Ωm. It can therefore be inferred from the standard resistivity table that the lithology of study area is composed of non-metallic type of mineral resources which are: clayey sand, lateritic clayey sand, sandstone and limestone. The estimated quantity in metric ton for the dominant lithology (sandstone, granite and limestone) is ± 10% of 1,257,142.9 which can be commercially explored. Keywords: Wenner-wenner array, outcrop, minerals, RES3DINV, block models.

(Quasi-)Real-Time Inversion of Airborne Time-Domain Electromagnetic Data via Artificial Neural Network

The possibility to have results very quickly after, or even during, the collection of electromagnetic data would be important, not only for quality check purposes, but also for adjusting the location of the proposed flight lines during an airborne time-domain acquisition. This kind of readiness could have a large impact in terms of optimization of the Value of Information of the measurements to be acquired. In addition, the importance of having fast tools for retrieving resistivity models from airborne time-domain data is demonstrated by the fact that Conductivity-Depth Imaging methodologies are still the standard in mineral exploration. In fact, they are extremely computationally efficient, and, at the same time, they preserve a very high lateral resolution. For these reasons, they are often preferred to inversion strategies even if the latter approaches are generally more accurate in terms of proper reconstruction of the depth of the targets and of reliable retrieval of true resistivity values of the subsurface. In this research, we discuss a novel approach, based on neural network techniques, capable of retrieving resistivity models with a quality comparable with the inversion strategy, but in a fraction of the time. We demonstrate the advantages of the proposed novel approach on synthetic and field datasets.

Aquifer characterization using vertical electrical sounding in Auchi polytechnic, Auchi, Edo State, Nigeria

The Schlumberger array method was used to carry out a total of eight (8) Vertical Electrical Sounding (VES) with a spread of 350 m in the study area. The Pasi 16-GL Terrameter was used to acquire the data. The data obtained were analyzed with the Winresist 1.0 software to obtain the curves of best fit to the theoretical models. The modeling program converted the apparent resistivity into true resistivity values in 1-D model curves. Five (5) to seven (7) layers were delineated which correspond to the topsoil, sandy clay, clayey sand, sand, dry sandstone and saturated sandstone. The depth to aquifer ranges from 95.0 to 169.6 m with resistivity values ranging from 324.3 to 1524.7 Ωm. Keywords: Apparent resistivity, Aquifer, lithology and vertical electrical sounding.

Magnetic and Geo-electrical Geophysical Techniques for Subsurface Delineation and Groundwater Assessment in Ras Matarma, Sinai

Groundwater constitutes the main source of the freshwater in Ras-Matarma, Sinai, which necessitates optimized management of it. In this context, geophysical ground magnetic, Schlumberger resistivity inversion, remote sensing (RS), geographic information system (GIS), and pumping tests were conducted. The magnetic survey comprised 56 profiles, whereas, Schlumberger resistivity survey were 27 VES. GIS and RS were implemented for watershed analyses in the area. Interpretation of the magnetic data separated significantly the shallow and deep structures with depths ranged from 300 to 1400 m. Qualitative and quantitative modelling of the inverted resistivity data demarcated effectively the fresh aquifer with true resistivity and thickness ranged from 22 to 210 ohm.m and 2 to 80 m, respectively. GIS aggregated all the aforementioned results along with electric and hydraulic parameters of the fresh aquifer.

Application of Vertical Electrical Sounding for Study the Proposed dam site at Wadi Ma’doo, Shabwah Governorate, Yemen

Application of geophysical investigation has been carried out using Vertical Electrical Sounding (VES) at the proposed site in wadi Ma’doo, Shabwah Governorate, Yemen to determine the geophysical parameters that can be used to evaluate the subsurface geological layering characteristics of the selection proposed site for dam construction. The Schlumberger array was used for the data acquisition. One-dimensional numerical inversion of individual DC resistivity was used to enhance the processing of the results for better achievement of the aim of the study. Model obtained from the 2D inversion of each VES were used for construction of geoelectric section which exhibit the main geoelectric characteristics of the geological units present in the site. The interpretation of the field data was carried out using the IP12WIN software, which converts the apparent resistivity as a function of electrode spacing to the true resistivity as a function of depth in two dimensions. The interpretation results showed that the geoelectric section consists of three layers namely: boulders and gravels, sandy to pebbly and hard limestone. The layer resistivities and thicknesses range from 18.17 to 746.20 Ω.m/0.20 to 1.084 m, 53 to 60 Ω.m/ 0.20 to 3.059 m and 455 to 1890 Ω.m, respectively. The investigation revealed that the limestone rocks is suitable for shallow foundation for proposed dam engineering structures.

IDENTIFIKASI BIDANG GELINCIR PADA DAERAH RAWAN LONGSOR DESA SRIMARTANI, YOGYAKARTA

Landslides are one of the disasters that often occur in Srimartani Village, Piyungan District, Yogyakarta. The biggest cause of landslides is the steep slope and the existence of a sliding plane on the slope. This study aims to identify the sliding plane on the slopes in Srimartani Village. This research was conducted using geoelectric method Wenner configuration with a: 10 m and n: 6. The data acquisition was taken in 6 lines. Data processing was done using Res2Dinv software and the result is a 2D true resistivity cross section. The results of the interpretation of the six lines indicate the existence of a sliding plane which is characterized by low resistivity contrast at the bottom and higher resistivity near the surface. Low resistivity (10 Ωm) is identified as clay rock and high resistivity ( 10 Ωm) above is identified as surface soil.