No abstract

The Upper Triassic Baluti Formation has been identified and mapped based on its log response in selected wells from the Zagros foldbelt in the Kurdistan Region of northern Iraq. A preliminary evaluation of the formation's source rock potential was made by Rock‐Eval screening analysis in four wells along a NW‐SE profile (Atrush‐1, Shaikan‐5B, Taq Taq‐22 and Miran‐2) with maturity determined from reflectance measurements in samples from well Taq Taq‐22. The Baluti Formation consists of thinly interbedded shales, carbonates and anhydrite ranging in thickness from 48 m in well Atrush‐1 to 118 m in well Miran‐2. The Rock‐Eval screening was conducted primarily on bulk cuttings samples plus selected picked cuttings. The TOC content is low to moderate (0.23 to 1.14 wt%). However, the shale content in many of the analysed bulk samples was relatively low, making assessment of the source potential problematic. The highest TOCs are recorded from the thickest analysed sections from wells Miran‐2 and Taq Taq‐22, where high‐gamma bituminous shales are present. Rock‐Eval Tmax values ranging from 295 to 438°C are not consistent with estimates of pre‐Zagros burial to depths of between 4600 m (Atrush‐1) and 6900 m (Miran‐2). The relatively low Tmax values suggest that the S2 response does not reflect kerogen pyrolysis in these samples and may be due to the presence of solid bitumen, which is observed in the Baluti Formation in at least three of the study wells (Taq Taq‐22, Miran‐2 and Shaikan‐5B). Little pyrolysable organic matter remains in the formation due to the interpreted deep pre‐Zagros burial and the consequent high maturity in Taq Taq‐22 (VR = 1.51%Ro) and Miran‐2 (estimated VR >2%Ro), and the poor source character in Atrush‐1 and Shaikan‐5B. Organic petrography suggests the presence of vestiges of Types I and II kerogen in Taq Taq‐22, with bitumen observed as stains in the matrix of the shales and also in the pores and fractures of interbedded dolostones. However, bitumen reflectance determinations for Taq Taq‐22 indicate an equivalent vitrinite reflectance maturity of no more than 0.93%Ro, which is significantly less than that of the indigenous vitrinite, implying the solid bitumen in this well is derived primarily from migrated hydrocarbons. Further detailed analysis is required, but the results suggest that the Baluti Formation may have sourced hydrocarbons in its depocentre which is identified in this study as covering a NW‐SE trending area between Bekhme and Sangaw.

The Early Cretaceous Sarmord Formation of northern Iraq has been studied from two subsurface sections, Kirkuk Oil Field (well K-229) and Khabbaz Oil Field (well KH-14), through petrographic, palynolofacies and organic geochemical analyses. The study reveals presence of two groups of microfacies settings. The first is the inner ramp, and the second represents the middle to outer ramp setting. The palynofacies study indicates that the amorphous organic matter is the predominant components (87-96%), followed by phytoclasts (3-11%) and palynomorphs (0-3 %). One main palynofacies type has been identified, which includes three secondary palynofacies types (PF1 A, PF1B, and PF1C) and refers to suboxic to anoxic basin condition. Thermal alteration index measured for the KH-14 well, indicated an immature to mature (TAI= 2, +2, 3) level, while, for the K-229 well mostly immature (TAI= -2, 2). The Rock-Eval analysis indicates that the TOC wt.% content of the samples range between 0.11% and 0.82% (average 0.29%) and 0.17% and 0.56% (average 0.35%) for K-229 well and KH-14 well, respectively. The Tmax values show that the most of analyzed samples of the both sections located in the immature zone, while the few samples from K-229 refer to mature zone. Another immature stage evidence is the shape of pyrograms with minor S1 and the large S2 peak, Tmax value less than 435°C, and PI around 1.0; all these criteria support the immature stage for these rock samples.

Sargelu Formation (Middle Jurassic) is well known to be one of the most important and wide distributed source rocks in the Middle East. In this study, nineteen cuttings samples from Sargelu Formation were studied from one subsurface section within Miran West Field (well MW-2) in Zagros Folded Belt, Kurdistan region of Iraq. The Formation was penetrated from the interval 2375m to 2475m, which is mainly composed of argillaceous limestone and shale. The Total Organic Carbon (TOC wt %) for all samples were calculated from the sonic and resistivity logs using Passey et al., method for TOC estimation from wireline logs. The range of TOC percentage in the selected interval is between 0.654 and 6.53%. In addition, all samples have been analyzed by Gas Chromatography/ Mass Spectrometry (GC/MS) in order to identify and study the biomarkers distribution in the selected rocks. The short chain n-alkanes between C15-C18, with isoprenoids pristane (Pr) and phytane (Ph) are dominants in the Sargelu formation. The average of Pr/Ph ratio in the samples was 0.95. Furthermore, most of the studied samples show unimodal envelope chromatograms, maximum peak carbon n-C15- n-C20, and low CPI values (0.89-1.17). The calculated odd over even predominance (OEP) for the studied samples show near value 1.0 (av. 0.94). The TOC values reflecting well preservation and high productivity of organic matter in reducing/anoxic depositional environment. Moreover, ratios of Pr/Ph indicating to anoxic and commonly marine carbonate environments; and also unimodal envelope of n-C15- n-C20 shows a predominance of marine input, and the organisms derived from phytoplankton, zooplankton and benthic bacteria with minor photosynthetic and terrestrial plants. The studied samples have C29 20S/(20S+20R) and ββ/ (ββ+αα) isomerization values ranging from 0.39 - 0.58 and 0.48 - 0.65 respectively, indicating high mature source rocks of Sargelu Formation in this well. In most studied samples, the C27 and C29 steranes predominate over the C28 steranes, reflecting a high contribution of aquatic planktonic-bacterial organic matter with a minor terrigenous organic matter input.

The Lower Cretaceous Sarmord Formation (Hauterivian–Barremian) has been investigated in this study. The selected M-2 Well is one of the wells belonging to Miran block, Sulaimani Governorate, Kurdistan Region of Iraq. The area of interest is situated in the High Folded Zone, Western Zagros Fold-Thrust Belt, being approximately 30 km far from Sulaimani City towards the northwest direction. The selected samples were analyzed by Rock-Eval pyrolysis, infrared spectroscopy, and also studied microscopically to determine the quality and quantity of organic matter, the level of thermal maturity, as well as the hydrocarbon generation potentiality. Rock-Eval pyrolysis data show that the total organic carbon for Sarmord Formation is between 0.83 wt.% to 1.55 wt.%, with an average value of 1.27 wt.%. The average and range of S1, S2, and genetic potential (S1+S2) are: 0.76 (0.55–1.09) mg HC/g rock, 0.82 (0.65 – 1.28) mg HC/g rock, and 1.58 (1.21 -2.37) mg HC/g rock, respectively. The average value of pyrolysable carbon (PC) and residual carbon (RC) are of 0.23 wt.% and 1.04 wt.%, respectively. The hydrogen index (HI) is between 47 and 98, with an average value of 66. The obtained data indicate that the Sarmord Formation has a satisfiable range of total organic carbon content, but the organic matter by itself has poor potential to generate hydrocarbons because of low amount of S2, HI, and PC. The Rock-Eval maturity parameters (Tmax and PI ) are undependable in this study. Because they are out of the acceptable range. The cutting samples in this well have been contaminated by solid drilling additives, which were identified during the petrographiocal study by their structure and low reflectance values. The double peaks of S2, solid drilling additives, are affected of disturbing maturity parameters of Rock-Eval data. The petrographic study proved that the samples mostly contain bituminite, which is disseminated predominantly within the clayey particles, with minor amounts of alginite. Additionally, weathered and degraded humic particles are interpreted as content of drilling mud. The kerogen types are mostly of Type II kerogen, because the vitrinite macerals are absent and we have an indication of alginite; which is one of precursos of formation of bituminite. This result is controversial with the graphical presentation of kerogen type by Rock-Eval and infrared microscopy, as they are interpreted as Type III gas-prone kerogen. The equivalent vitrinite reflectance for the studied section ranges between 0.73-0.81%, with the values close to 0.80% being more accurate as were measured in homogenous solid bitumens. The obtained values indicate maturation within the oil window. While based on infra red spectroscopy, maturation is between 0.80 to 1.10, suggesting to higher maturation level compared to vitrinite reflectance values.