Dolomitization and Hypogenic Dissolution of the Eocene Avanah Formation, Iraqi Kurdistan

This study constrains the mechanism of extensive dolomitization and its impact on reservoir quality of the shallowwater marine ramp carbonates of the Avanah Formation (Eocene), Iraqi Kurdistan. The presence of shoal deposits, which semiisolate a lagoon water body from the open marine, suggests that dolomitization was by seepage reflux of brines. Nevertheless, the absence of eogenetic gypsum/anhydrite in the dolostones succession indicates that the dolomitizing fluids were mesohaline/penesaline brines formed during cycles of relative sea level (RSL) fall. Dolomitization resulted in the formation of abundant intercrystalline and moldic/vuggy pores. Restriction of dolomitization and related reservoir quality improvement to the lower part of the formation is attributed to an overall 3rd order fall in the RSL. Conversely, the lack of dolomitization in the upper part of the formation is attributed to deposition during 3rd order marine transgression, which prevented severe restriction and evaporation of the inner ramp and, consequently, inhibited the development of dolomitizing brines. It is suggested that hypogenic dissolution (karstification) by upward flow of aggressive fluids along faults and fractures during the Zagros Orogeny caused dissolution and considerable porosity and permeability improvement of the dolostones. A greater extent of dolostones dissolution in the flanks, which was accompanied by calcite cementation, compared to the crest, reflects the role of oil emplacement in the retardation of diagenetic reactions

Fracture, VUG and Intercrystalline Porosity and Permeability Analysis from Well Logs of LIRTIM Oil Field, Iraq

Carbonate reservoir unarguably contributes over 50% of presently produced crude oil in the world today especially from the middle-eastern part of the world with appreciable amount of reserve estimate yet unexplored. Deposition, sedimentation, diagenesis and other geological features of carbonate rocks has been studied leading their classification into: mudstone, wackestone, packstone, grainstone, boundstone and crystalline carbonate rocks. These are all characterised by various features such as fractures and vugs which influences its petro-physical behaviour. The study of the main features of carbonate reservoir using Archie’s cementation exponent “m” is an acceptable method of verifying the geological features in the reservoir which actually contribute to rock fluid properties and other production attributes of the reservoir. This was verified for some reservoir using well log values for Lirtim oil field in Iraq. The dominating geological features of the field were verified from a graphical representation of the different data from field reservoir. The reservoirs used as case studies in the research were also classified into different carbonate rocks using a graphical plot of their permeability against porosity values. This result gives a clue of the textural and grain size characteristics as well as the effective pore sizes of the reservoir. This method of analysis makes it easier to evaluate the post diagenetic strength of the reservoir rocks and fluid hosting capability in view of recovering hydrocarbon in the are

Reservoir characteristics of the middle Eocene Avanah Formation in Erbil governorate, northern Iraq: integration of outcrop and subsurface data

The current work investigate the petrophysical characteristics of the Middle Eocene Avanah Formation in the Erbil Governorate using IP software to analyze the well data, integrated with the petrographic investigation of the formation in the nearest outcrop in the Gomaspan section.Well logging data revealed that the main lithology of the formation is limestone and dolostone while the lithology in the Gomaspan section is composed of limestone, dolomitic limestone, marly dolomitic limestone, and thin beds of shale. The lower dolomitic unit in the subsurface section of theformation is believed to be the most suitable reservoir unit due to good petrophysical characteristics including, low water saturation, high porous medium, and the presence of movable hydrocarbon. To measure porosities, a variety of well logging techniques were used in this study. The investigated formation was divided into Avanah dense (limestone unit) and Avanah porous (dolostone unit) based on their porous components. The petrographic study shows that most pore types of the formation are secondary and represented mainly by vuggy, moldic, intercrystalline, and fracture types. Most of the fractures in the upper limestone units are filled by calcite cement. The study claime

Depositional setting of the Jaddala Formation at Kirkuk and Bai Hassan Fields, Kirkuk Area

يمثل تكوين الجدالة في حقول كركوك وباي حسن ترسيب على مصطبة جيريه على شكل رف مفتوح. أظهر تحليل السحنات المجهرية أن الترسيب كان ضمن ثلاثة مناطق وهي: الرف العميق وأسفل المنحدر والحوض العميق. يتكون الجدالة من أربع دورات ترسيبيه ذات الرتبة الثالثة، وتمثل هذه الدورات تعاقب فترات لارتفاع مستوي سطح البحر وثباته.  يمكن الاستنتاج من طبيعة التماثل وسمك هذه الدورات بأن التأثير التكتوني هو العامل الرئيسي المسؤول عن تطور هذه الدورات في حوض ذو معدل تجلس عالThe Jaddala Formation in Bai Hassan and Kirkuk oil fields was deposited on a carbonate platform with an open shelf setting. Microfacies analysis revealed that deposition took place within three zones; they include the Toe of slope, Deep shelf, and Deep basin. The succession consists of four third order cycles representing successive intervals of relative sea level rises and stillstand. The nature of cycle symmetry and thicknesses suggest that the tectonic component is the main controlling factor on cycle development in highly subsiding basin

Sedimentology and reservoir characteristics of the oligocene-early miocene carbonates (Kirkuk group) of southern Kurdistan

Kirkuk Group Formations (in addition to Avanah and Jaddala Formations) of southern Kurdistan were studied in order to determine biostratigraphy, chronostratigraphy and sequence stratigraphic relationships, in addition to major sediment producing environments and type of platform configuration. As well as to determine the paragenetic sequences with special attention to micrite diagenesis and its effect on microporosity. Five biozones were identified in the study area in which two of them from Middle- Late Eocene: Alveolina biozone (AL) and Discocyclina biozone (DI) with three biozones from the Oligocene-Early Miocene of Kirkuk Group: Nummulites fichteli biozone (NF); Praerhapydionina delicata biozone (PD) and Austrotrillina howchini biozone (AH). Twenty two microfacies were identified and interpreted as having been deposited in a ramp setting based on lateral variations of the microfacies; gradual deepening with no evidence of slope break or effective barrier. A depositional model has been generated from the overall palaeoenvironmental interpretations of the microfacies in which the analysed microfacies indicates palaeoenvironments ranging from terrestrial to open marine settings; nine major depositional environmental zones have been identified and correlated with the standard Cenozoic ramp model of Buxton and Pedley (1989). These zones distributed across the ramp setting dipping southwest, in which zone 1 is terrestrial deposit; zone 2, 3, 4 and 5 are belonging to inner ramp; zone 6, 7 and 8 are belong to middle ramp and zone 9 is belong to outer ramp and basinal settings. A paragenetic sequence has been derived recording eleven diagenetic processes affecting the Kirkuk Group which are subdivided into an eogenetic, mesogenetic and telogenetic stages. Furthermore, micrite matrices were studied from both shallow and deeper marine settings using SEM, trace elements and carbon/oxygen isotopes; the result shows the different sources; inner-mid ramp muds have a hemi-pelagic source and could have been mostly sourced from high-Mg calcite benthic foraminifera and red algae, and possible partial aragonite dominating; in contrast, the outer ramp matrices, were sourced from plankton, are largely composed of low-Mg calcite, as they are mineralogically stable. Although the exact origin would be difficult to ascertain after diagenesis. From the above two different rock fabrics, two distinct pore systems were identified: (1) low microporosity inner-mid ramp microfacies, it was sourced from metastable precursors and were recrystallized and replaced under meteoric waters, undergoing loss of primary porosity; (2) higher microporosity outer ramp/basinal microfacies, composed of more stable low-Mg calcite that underwent less recrystallization and retained some primary porosity. The Kirkuk Group succession comprises of two shallowing upward 4th order cycle within one 3rd order cycle located between two unconformable surfaces at lower and upper boundaries which can be correlated to the global regression of sea level. The first 4th order cycle is located at Rupelian and composed of only the Sheikh Alas Formation and the second 4th order cycle is located at Chattian-Early Aquitanian and composed of the Bajawan, Anah, Azkand and Ibrahim Formations. Two different depositional sequences with different thicknesses were developed due to the synsedimentary Khanaqin Basement Fault which cross-cuts the study area and was activate during deposition

Integrated depositional model of the Carbonate Kirkuk Group of Southern Kurdistan-Iraq

The carbonate Kirkuk Group succession hosts major hydrocarbon reserves in the southern Kurdistan-Northen Iraq. This is why investigations into this succession started a long time ago, especially for oil exploration. In this research numerous microfacies were identified from the Kirkuk Group and interpreted as having been deposited in a ramp setting based on lateral variations of the microfacies; gradual deepening with no evidence of slope break or effective barriers. A depositional model has been generated from the overall palaeoenvironmental interpretations of the microfacies in which the analysed microfacies indicate palaeoenvironments ranging from terrestrial to open marine settings; nine major depositional environmental zones have been identified and correlated with the standard Cenozoic carbonate ramp model. These zones distributed across the ramp setting, dipping southwest, in which zone 1 is a terrestrial deposit; zone 2, 3, 4 and 5 belong to the inner ramp; zone 6, 7 and 8 belong to the middle ramp and zone 9 belong to the outer ramp and basinal settings. Key words: Kirkuk Group, microfacies, Oligocene, Carbonate, Kurdistan, Iraq

Crude oil and oil brine seeps: sources, detection and environmental effects in soil and water, Kirkuk NE Iraq

Natural hydrocarbons have extensively contaminated both the hydro-lithospheres, damaging the environment and the health of the people living in the Kirkuk region of North-East Iraq, which is an area with a world´s significant crude oil reserves as well as various hydrocarbon seeps and brines. The study area is located in the Zagros fold-thrust belt, within the Low Folded Zone in the northeast of the Mesopotamia basin. Complex fracture systems and faults frequently cut across the Eocene, and middle Oligocene limestone reservoirs and the evaporates Miocene cap rock. High-density maps of the detected faults and lineaments within Fatha Formation have interpreted as potential seepage locations, even for seeps that are not exposed on the surface. The present thesis aims to investigate hydrocarbon seeps, and oil brine seeps contamination impact on the surface, groundwater as well as the soil’s physical and chemical properties. Therefore, various methods were used starting by identifying the origin of the seeps as a base to assess the source and ending by estimating the contamination level of hydrocarbons and related brines in water and soil directly or remotely. The essential concept of the present thesis is based on the known hydrocarbon seepage sits – which were recorded for hundreds of meters on the surface – and the sub-surface properties of the stratigraphy and hydrogeology conditions. In addition to the several reports and studies, the primary data source was based on the wide variation of the collected samples, i.e., crude oil and brine water samples from the selected oil reservoir to define the reservoir characterization and migration level. Moreover, the reservoir oil types were used to compare them with surface crude oil seeps samples. The surface and groundwater from the selected location and different aquifers beside soil and rock samples explained the aquifer's recharge and led to the appropriate speculation of the hydrodynamic and hydrogeological conditions. The measurements included: a) oil density, organic and inorganic components and biomarkers for crude oil samples, and polycyclic aromatic hydrocarbon PAHs; b) hydrochemistry, stable isotopes; and c) the spectral reflectance behavior of crude oil and different contaminated soil samples, organic components (organic carbon (OC) and total petroleum hydrocarbons (TPHs)) and x-ray diffraction to explain the chemical composition of the soil samples. The multiple data were transformed into one database, and the results were used to complete the final hypotheses in a conceptual model, which explains the mixing mechanism of crude oil and brine seeps with the surrounding environment. The strontium isotopes (87Sr/86Sr) showed the mixing processes between shallow groundwater resources, uprising oil field brines and differentiates it from the dissolution of gypsum and halite from the Fatha Formation. The final discussion and conclusions connect all of the results and try to simulate the sub-surface hydraulic conductivity and highlight the contamination zones that were explained in the final comprehensive conceptual model, enriching our knowledge of the petroleum and the hydrogeology systems of the selected fields within the Zagros fold-thrust belt. The obtained results mainly highlight the reasons behind the environmental consequences that can be a threat to the human health. The conclusion of this study opens the door to compare the findings with other locations within the study region, which contains similar complex stratigraphy and structures

Petrophysical Investigation of the Khurmala Formation in Taq Taq Oil Field, Zagros Folded Belt

The Tertiary rocks of Khurmala Formation in the Taq Taq oil field have been studied using wireline log analysis, drilling cutting descriptions with integration of mud logging report, and test results for understanding reservoir potentiality and fluid distribution. The formation comprised dolostone and dolomitic limestone with an intercalation of clay layers between the recognized beds. The formation has variable thickness throughout the field, 99.8 m from the northeastern limb and 109 m in the southeastern plunge. The calculated shale volume in the studied interval shows a high rate of the clay contents which in some points the gamma ray has 100% of shale. The corrected log-derived bulk porosity subdivided the Khurmala Formation into 5 porosity units from the top to the bottom including (Kh-1, Kh-2, Kh-3, Kh-4, and Kh-5). The first (Kh-1), third (Kh-3), and fifth (Kh-5) porosity units have the average porosity ≥0.10 (10%) that can be considered as good reservoir unit in terms of porosity, whereas the shale contents reduced the reservoir quality of these units. However, well hydrocarbon entrapment through interconnected fractures and fault in the other Tertiary reservoir was recorded in Taq Taq field , but the weak connectivity of the pores in the Khurmala Formation caused this rock interval remains as water bearing zone

Maastrichtian - upper Eocene ostracoda of the subfamily Trachyleberidinae from Iraq, Jordan and Syria

Abstract available: p 16