Study of Petrophysical Properties of the Yamama Formation in Siba Oilfield

Evaluating a reservoir to looking for hydrocarbon bearing zones, by determining the petrophysical properties in two wells of the Yamama Formation in Siba field using Schlumberger Techlog software. Three porosity logs were used to identify lithology using MN and MID cross plots. Shale volume were calculated using gamma ray log in well Sb-6ST1 and corrected gamma ray in well Sb-5B. Sonic log was used to calculate porosity in bad hole intervals while from density log at in-gauge intervals. Moreover, water saturation was computed from the modified Simandoux equation and compared to the Archie equation. Finally, Permeability was estimated using a flow zone indicator. The results show that the Yamama Formation is found to be mainly limestone that confirmed by cuttings description and this lithology intermixed with some dolomite, in addition to gas and secondary porosity effects. Generally, the formation is considered clean due to the low shale volume in both wells with the elimination of the uranium effect in well Sb-5B. The calculated porosity was validated by core porosity in YC and YD units. Modified Simandoux gives a better estimation than the Archie equation since it takes into account the conductive of matrix in addition to the fluid conductivity. Five equations were obtained from porosity permeability relationship of core data based on five hydraulic flow units reorganized from the cross plot of reservoir quality index against normalized porosity index. The overall interpretation showed that YC and YD units are the best quality hydrocarbon units in the Yamama Formation, while YA came in the second importance and has properties better than YB. Moreover, YE and YFG are poor units due to high water saturation.

Utilization of Digital Mapping and Outcrop Model to Assess Reservoir Characterization and Quality Index: Study Case from Ngrayong Formation in the Randugunting Block, East Java

Digital mapping and digital outcrop modeling are the current state of the art in geology that incorporated traditional field geological mapping and digital technique. Integration of these two techniques produce a realistic earth model that could help to understand its petroleum prospectivity. Our study aims to provide a workflow and illustrate preliminary reservoir characterization as well as reservoir quality index assessment from mapping and digital outcrop model in the area with lack of subsurface dataset, such as limited well and seismic data distribution due to an early exploration stage. We utilized a mix siliciclastic-carbonate outcrop of Ngrayong formation in the Randugunting Block, East Java, collecting several measuring sections and followed by rock sampling per certain interval. Drone acquisition was implemented in the area of interest to generate high resolution 3D outcrop model. The measuring section later on tied with digital outcrop model, producing structural and stratigraphic model. In addition, subsurface reservoir parameters from well and seismic were integrated in order to add accuracy value to our model from surface perspective. Facies and properties model were populated and Reservoir Quality Index (RQI) was calculated to suggest any potential flow units. Our results show excellent alignment between structural, facies, properties model and reservoir quality index to illustrate characteristic of reservoir in the study area. Uncertainty comes from geostatistical approach, data acquisition quality, and theoritical assumption where multiple sensitivity analyses were conducted to optimize the model. Methodology presented in this study can help to assess the reservoir characterization and quality index in the early exploration stage. Thus, reservoir distribution, potential flow units and petroleum prospectivity will be mostly predictable. In addition, this study has successfully visualized and manifested preliminary 3D subsurface reservoir characterization in area with lack of subsurface dataset and reduced significant capital expenditure cost (CAPEX) for acquisition new data on early exploration phase.

Rock typing based on hydraulic and electric flow units for reservoir characterization of Nubia Sandstone, southwest Sinai, Egypt

The present work describes and evaluates the reservoir quality of the sandstone of the Nubia Formation at the Gebel Abu Hasswa outcrop in southwest Sinai, Egypt. Hydraulic flow unit (HFU) and electrical flow unit (EFU) concepts are implied to achieve this purpose. The Paleozoic section made up of four formations has been studied. The oldest is Araba Formation followed by Naqus formations (Nubia C and D) overlay by Abu Durba, Ahemir and Qiseib formations (Nubia B), where the Lower Cretaceous (Nubia A) is represented by the Malha Formation. The studied samples have been collected from Araba, Abu Durba, Ahemir and the Malha formations. The hydraulic flow unit (HFU) discrimination was carried out based on permeability and porosity relationship, whereas the electrical flow unit (EFU) differentiation was carried out based on the relationship between formation resistivity factor and porosity. Petrographic investigation of the studied thin sections illustrates that the studied samples are mainly quartz arenite. Important roles to enhance or reduce the pore size and/or pore throats controlling the reservoir petrophysical behavior are due to the diagenetic processes. The present study used the reservoir quality index (RQI) and Winland R35 as additional parameters applied to discriminate the HFUs. The study samples have five hydraulic flow units of different rock types, where the detected electrical flow units are only three. The differences between them are may be due to the cementation process with iron oxides that might act as pore filling, lining and pore bridging, sometimes bridges helping to decrease permeability without serious reduction in porosity. The reduction between the number of EFUs and HFUs comes from the effect of diagenesis processes which is responsible for a precipitation of different cement types such as different clay minerals and iron oxides.

Petrophysical characterization, microfacies analysis, and diagenetic attributes of the Lower Jurassic surface analog sequence in Gebel El-Maghara area, north Sinai, Egypt

This study concerns with the petrophysical characteristics of the Lower Jurassic surface analog in Gebel El-Maghara area (from base to top Mashaba, Rajabia, and Shusha formations), north Sinai, Egypt and implementation of the mineral components and diagenetic controls on reservoir characteristics. A full set of petrophysical measurements including porosity (∅He), permeability (k), grain and bulk densities (σg and σb, respectively), and true formation resistivity factor was applied. The Lower Jurassic sequence is subdivided into five hydraulic flow units (HFUs) that consist of three reservoir rock types (RRTs). These RRTs are composed of three microfacies association (MFAs). The RRT1 plug samples consist of the mostly clastic MFA1; they are porous, permeable, and have good reservoir quality that is using the flow zone indicator (FZI), and the reservoir quality index (RQI). The lowest reservoir quality is assigned to the RRT samples which are mostly composed tight carbonates. Based on the petrographical studies, SEM imaging, and the XRD analysis, dissolution and fracturing slightly enhanced the reservoir potentiality of the RRT1 samples, whereas physical compaction, tight cementation, and authigenic clay content (kaolinite, hematite, and goethite) are responsible for deterioration of the reservoir properties of RRT3 samples and reduction of the RRT2 samples.

Lithology estimation from a multicomponent 3D-4C OBC seismic survey over a clastic reservoir in the Arabian Gulf

ABSTRACT In 2002, Saudi Aramco conducted its first 3D, 4-component (4C) ocean-bottom cable (OBC) seismic survey in the Arabian Gulf. The main objective was to delineate the middle Cretaceous Upper Khafji Sand Stringers Reservoir overlying the massive Main Khafji Sand Reservoir in the Zuluf field. The Upper Khafji Sand Stringers Reservoir in the Wasia Formation is typically characterized by weak acoustic impedance contrasts. A pre-survey modeling study, based on the logs of compressional (P) and shear-wave (S) velocities (Vp and Vs), indicated that converted compressional-to-shear waves (P-S) could better-image the structure and stratigraphy of the target reservoir. Commensurate with the objectives of the experiment, a pilot 100-square-kilometer survey was acquired with an inline swath-shooting geometry that employed two seabed receiver cables, with a symmetric split-spread deployment of the 4-C sensors. The acquisition geometry consisted of six sail lines per swath with a single-boat, dual-source, flip-flop configuration. The data were processed through dual-sensor summation, horizontal-component rotation and P-P/P-S pre-stack time migration. Post-stack enhancement using non-stationary Gabor deconvolution proved beneficial in compensating for the missing high frequencies in the acquired converted-wave data. Well-to-seismic calibration for both P-P and P-S data at five wells aided in the interpretation of the data. Five horizons were interpreted and correlated between the P-P and P-S sections. The horizons were analyzed using both amplitude and interval times such that the lateral variations of the Vp/Vs ratio of the Upper Khafji Sand Stringers Reservoir could be mapped. A region of low Vp/Vs ratios in the northwest quadrant, obtained from the isochron interval-time analysis, was correlated with higher ‘net sand’ pay at a hidden well located in the middle of this region. These results were further corroborated by seismic facies analysis and provide a qualitative reservoir quality index in the Upper Khafji Sand Stringers Reservoir.