An integrated sedimentological and sequence stratigraphic analysis of the mixed carbonate and clastic Albian Mauddud Formation in the Bahrah and Sabiriyah fields provides an improved understanding of this important reservoir in north Kuwait. The reservoir comprises two broad stratigraphic units: the lower Mauddud represents the culmination of a long-term transgressive retreat of the underlying Burgan delta system, whereas the overlying upper Mauddud records a low-gradient carbonate shelf or ramp system. A highly layered reservoir architecture of carbonate and clastic facies suggests a combination of high-frequency relative sea level and/or climatic fluctuations. Sedimentological analysis and regional correlations reveal a complex mixed carbonate-clastic system in which there is a tripartite arrangement of proximal coarse grained deltaic, distal prodeltaic, and offshore to along-strike carbonate facies. These form correlatable reservoir units bound by flooding surfaces and/or significant influxes of clastic sediment. The distribution of clastic and carbonate facies produces a pronounced variation in reservoir properties, between the neighboring Bahrah and Sabiriyah fields of north Kuwait. Primary stratigraphic and depositional reservoir heterogeneities are controlled by carbonate facies transitions from poor quality, micritic lagoonal facies to high-quality, grain-rich shoals and localized, reworked rudistid build-ups. These carbonate facies are cyclically layered with deltaic sandstone and prodeltaic shales. In combination with secondary diagenetic (e.g., cementation and dissolution) and structural characteristics (e.g., faults and fractures), this facies variability exerts a control on reservoir quality and produces a complex mosaic of reservoir heterogeneity. Reservoir variability controls differences in production performance of the neighboring fields, and these have been accommodated by contrasting field development strategies.

The Mauddud Formation, a late Albian-aged carbonate oil reservoir, is one of the main oil producers in Kuwait, however, it exhibits unreliable oil production from the Bahrah Field. The Mauddud Formation in the Bahrah field is divided into two sub-structures by a series of E-W faults and shows a slight degradation in oil quality (∼5API) within the up-dip structure. Intersections of the E-W faults with NW-SE faults are associated with deep-seated seismic pipes, which culminate in pull-up features, creating the overlying sag-like features. Additionally, the Mauddud Formation shows evidence of baroque (saddle) dolomite in fracture cements and replacing clasts. The baroque dolomite have 3He/4He ratios ∼0.3 times higher than atmospheric values. Taken together, this seismic and petrographic evidence suggests that the Mauddud Formation experienced an ingress of radiogenic, crustal fluids, potentially sourced from the basement. Seismic pipes, therefore, are interpreted to be the product of the upward movement of hydrothermal fluids that breach seal rocks, causing oil to escape and subsequent calcite cementation. An integrated map of a basement magnetic anomaly and current exhalative features on the present-day surface shows evidence of a relationship with fault locations on the level of the Mauddud Formation that were rejuvenated and associated with the remigration of oil. This study provides an exceptional example of a seal breach in one of the world's most prolific hydrocarbon provinces. It also indicates the importance of a multidisciplinary, multi-scale approach extending from the basement to the surface in order to understand seal breach in carbonate petroleum systems. The overall data is used to assess the main factors that effected the integrity of the seal when this latter is breached by hydrothermal fluids.

The Khuff Formation was deposited in shallow marine to tidal flat environments during Late Permian, directly after the Hercynian Orogeny. The porosity can classified into two categories: 1) Primary intergranular macroporosity of peloidal/ oolitic grainstone. 2) Secondary solution-enlarged porosity and jacked-open stylolite. The primary fabrics are completely dolomitized and replaced by subsequent anhydrite that dramatically reduce depositional porosity. Furthermore, vug- and fracture filling cementation of anhydrite occludes secondary porosity and close remnant pore spaces. There is no evidence of oil bearing from core data and reservoir quality is essentially negligible. Different types of anhydrite can be distinguished under a petrographic microscope including fine-grain “chicken-wire”, porphyrotopic, acicular-felted, lath-shaped, bladed and blocky anhydrite. Petrographic analysis determine that the precipitation of anhydrite coeval early diagenetic conditions related to evaporative concentrated waters in arid-region (e.g. environment enclosed lagoon or supratidal domain). However, Anhydrite also occur as precipitates of hydrothermal fluids after burial, showing association of stylolitic surfaces and pyrite nodules. It expected that the burial diagenesis cause migration and re-precipitation of anhydrite solutions into adjacent and up-dip strata. Therefore, this study suggests that the Khuff Formation away from crest part of Burgan field, where less fluid-rock interactions, provides better potential of hydrocarbon entrapment. This study present an example of destructive impact of burial diagenesis on world-class hydrocarbon province.

AbstractThe petrophysical properties of reservoirs represent several factors such as reservoir quality and volume of oil saturation (PHI, PERM and SW). The relationship between these factors is complementary; migration and trapping of oil is critical to reservoir quality preservation and it is often compromised by closure of the structure, quality of the seal and tectonic activity. In Kuwait, the Mauddud Formation in Bahra Field (BAMA) does not show a sustainable oil production, unlike the Mauddud Formation in Sabriyah Field (SAMA), although both fields are neighboring and separated only by a saddle. Well data reveals a considerable reservoir complexity that distinguishes BAMA from SAMA, which cannot be easily ascribed to facies variability. Geological data (seismic, wireline logs, core and thin sections) indicates four main differences in BAMA compare to SAMA. First, general stratigraphic thinning of carbonate sequences due to its palaeo-proximal position that made it more susceptible to erosion and increased clastic supply and, secondly, a sandier seal rock. Thirdly, there is a degradation of reservoir quality where the average oil saturation and the porosity are 50% and 15% respectively, compared to 90% and 20% In SAMA. Finally, three fault orientations occur in BAMA including a distinct E-W trend, that does not observed in SAMA. Three main possible hypotheses postulated in this study are based on early results.Cementation by meteoric phreatic cements occluded the porosity in BAMA before the arrival of oil. The fresh water penetrations was facilitated by the sandier seal and proximal paleo- environment in BAMA.Onset and partial growth of the trapping structure in SAMA, allowed an earlier oil expulsion to become trapped, retaining secondary porosity, whilst oil bypassed BAMA traps due to later structural growth.The E-W faults in BAMA were responsible for oil migration vertically by breaching the seal rock. The leakage was followed by an influx burial fluids which re-activated cementation in BAMA that was arrested for a short period by the arrival of oil.

A quantitative model of the spatial distribution of reservoir properties is key to understanding reservoir heterogeneity. Special Core Analysis (SCAL) data is essential input for static and dynamic modeling of heterogenous reservoirs. To provide high-quality reliable data, the SCAL program should use the right samples from the core. Conventionally, integrated geological and petrophysical approaches are applied to select samples but they generally lack consistency and seldom incorporate upscaling options. This paper presents a novel methodology for core characterization and SCAL sample selection. SCAL data is used as input for spatial distribution of reservoir properties in a static reservoir model. The analysis is performed in siliciclastics and carbonate reservoirs from wells in the Bahrah Oil Field. An integrated X-ray, CT scanning, geological, and conventional core analysis approach is applied for understanding the reservoirs. We demonstrate the efficiency of dual-energy CT imaging in producing continuous whole core scans at 0.5 mm (500 micron) spacing and in deriving bulk density (BD) and effective atomic number (Zeff) logs along the core intervals. The high resolution 3D CT images improved the sedimentological descriptions of the core and the X-ray CT-derived numerical data (BD and Zeff) are used to derive porosity and mineralogy along the whole core sections. This information is then converted into lithology logs which predicted the cross-well correlation and enhanced the previously established correlation from conventional core descriptions. BD and Zeff cross plots suggested four lithotypes in the core intervals and the corresponding lithology log helped in deriving the percentage of each type: 1. Low BD (high pososity) carbonate formed around 20% of the whole cores. 2. High BD (low porosity) carbonate formed around 36% of the whole cores. 3. Low BD (high porosity) sandstone formed around 28% of the whole cores. 4. High BD (low porosity) sandstone formed around 16% of the whole cores. The data provided a unique capability for ensuring that the plugs adequately and correctly represented the lithotype variations along the core. The overall procedure helped minimize uncertainties in defining the rock types and effectively assign those rock types to the selected samples and core intervals.

PreviousNext No AccessSEG Technical Program Expanded Abstracts 2012Geophysical Approach to Naturally Fractured Reservoir Characterization and Its Applications, a case from Kuwait.Authors: Antonio PicoAnjaneyulu SingavarapuAbdul Aziz Ali SajerRosmari UstaSayed BehbehaniMefarreh Al-DkheelAntonio PicoKuwait Oil CompanySearch for more papers by this author, Anjaneyulu SingavarapuKuwait Oil CompanySearch for more papers by this author, Abdul Aziz Ali SajerKuwait Oil CompanySearch for more papers by this author, Rosmari UstaKuwait Oil CompanySearch for more papers by this author, Sayed BehbehaniKuwait Oil CompanySearch for more papers by this author, and Mefarreh Al-DkheelKuwait Oil CompanySearch for more papers by this authorhttps://doi.org/10.1190/segam2012-0670.1 SectionsSupplemental MaterialAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail Abstract Fractures play a major role in the production from low permeability carbonate reservoirs. In this paper, an integrated approach for fracture characterization using seismic attributes is attempted. In order to get better detection and interpretation of fractured zones, multi seismic attributes including volume curvature, coherency etc. were applied to reduce the uncertainties associated with the seismic data, and some geological constraints including faults-associated fracture zones etc. were used to interpret and identify the fracture features correctly. The Makhul Formation in Kuwait is a tight and low porosity fractured reservoir and is an important target for hydrocarbon exploration. From a preliminary 3D seismic attribute analysis of the area of interest, the attributes of curvature (positive and negative), semblance and ant tracking have been the most helpful tools in predicting where a high density of fractures might exist and their general orientation. Permalink: https://doi.org/10.1190/segam2012-0670.1FiguresReferencesRelatedDetailsCited By3D seismic discontinuity attributes analyses for low – permeability reservoir sand fractures characterisation: an onshore example from Niger delta, Nigeria19 January 2021 | NRIAG Journal of Astronomy and Geophysics, Vol. 10, No. 1 SEG Technical Program Expanded Abstracts 2012ISSN (print):1052-3812 ISSN (online):1949-4645Copyright: 2012 Pages: 4609 Publisher:Society of Exploration Geophysicists HistoryPublished: 25 Oct 2012 CITATION INFORMATION Antonio Pico, Anjaneyulu Singavarapu, Abdul Aziz Ali Sajer, Rosmari Usta, Sayed Behbehani, and Mefarreh Al-Dkheel, (2012), "Geophysical Approach to Naturally Fractured Reservoir Characterization and Its Applications, a case from Kuwait.," SEG Technical Program Expanded Abstracts : 1-5. https://doi.org/10.1190/segam2012-0670.1 Plain-Language Summary PDF DownloadLoading ...