In this study collected samples of Chia Gara Formation in Atrush, Shaikhan and Sarsang oilfields are used to geochemical characteristics of organic matter in this formation. This determination was based on Rock-Eval pyrolysis and Biomarker analyses. The Chia Gara Formation can be considered as good to excellent source rock; it’s TOC content ranges from 1.14-8.5wt% with an average of 1.85%, 3.91%, and 6.94% in Atush-1, Mangesh-1 and Shaikhan-8 wells respectively. The samples of Chia Gara Formation contain kerogen type II. These properties are considered optimal for oil generation. The low oxygen index (OI) and pristane/phytane (Pr/Ph) ratios (Average 20.73, 0.61 respectively) and high hydrogen index (HI) (average 637.6) indicate that the formation was deposited under anoxic condition. According to regular sterane (C27%, C28%, C29%) and terpanes ratios (C29/C30, C31/C30 hopane), the formation was deposited in marine environment. The average value of the Carbon Preference Index (CPI) is one with Tmax values of more than 430 ºC; these indicate peak oil window for the selected samples. Overall, the 20S/(20S+20R), ββ/(ββ+αα)C29 steranes and 22R/(22R+22S)C32homohopane, with Ts/ (Ts+Tm), and moretane/ hopane ratios point to a mature organic matter and to the ability of the formation to generate oil.

The current study represents an evaluation of the petrophysical properties in the well Shaikhan-8 for the Garagu, Sarmord and Qamchuqa formations in Shaikhan oilfield, Duhok basin, northern Iraq. The petrophysical evaluation is based on well logs data to delineate the reservoir characteristics. The environmental corrections and petrophysical parameters such as porosity, water saturation, and hydrocarbon saturation are computed and interpreted using Interactive Petrophysics (IP) program. Neutron-density crossplot is used to identify lithological properties. The Qamchuqa Formation in the Shaikhan oilfield consists mainly of dolomite with dolomitic limestone, and the average clay volume is about 13%; while Sarmord Formation composed of limestone and dolomitic limestone, the average clay volume in this formation is about 19%; also the Garagu Formation consists mainly of limestone and dolomitic limestone in addition to sandstone and claystone, the volume of clay in the Garagu Formation is about 20%. Pickett plot method is used to calculate formation water resistivity (Rw), saturation exponent (n) and cementation exponent (m) the values are 0.065ohm, 2, and 2.06 respectively. The porosity ratio (Ø) of the Qamchuqa Formation ranges between 7-15%; this indicates that the lower part of the formation has a poor-fair porosity (7%), while the upper part of the formation has a good porosity (15%). The porosity value decrease toward Sarmord Formation especially in the lower part of the formation, it has a poor porosity (5%), whereas this value reaches to 13% in the upper part of the formation, indicates for fair porosity. Garagu Formation has good porosity, reaches 20% in the lower part, but in the upper part of the formation, this value decreases to 3%. Water saturation (Sw) value which is calculated by Archie equation ranges between 14-33%, while saturation in the flushed zone (Sxo) ranges between 52-73%, these indicate for good movable hydrocarbons are present in the studied interval (840-1320m), and from the total 480m the Early Cretaceous formations in well Shaikhan-8 have 178m pay.ABSTRACT

This study was covered palynofacies and paleodepositional environment of the Chai Gara, Garagu, Sarmord and Qamchuqa formations along Atrush, Shaikhan and Sarsang oilfields in Duhok Region northern Iraq. Six main types of palynofacies were recognized within the studied formations. The palynofacies one (PF.1) and two (PF.2) are appeared in Chia Gara Formation, these two types of palynofacies are characterized by dominant amorphous organic matters (AOM), especially in PF.2 which reaches to 90%, moderate palynomorphs content ranges between 5 – 59%, whereas the phytoclasts are relatively low percentages (1 – 5%). The identified palynofacies indicate that the paleodepositional environment of the Chia Gara Formation is distal suboxic-anoxic basin (IX) to dysoxic-anoxic shelf (VII). Garagu Formation is represented by palynofacies three (PF.3) and palynofacies four (PF.4), the former one is characterized by the abundant of palynomorph, ranges between 41 – 85% (comprised mainly of pollen, spores, foraminifera test lining and few dinoflagellates), while the latter one is rich by amorphous organic matter which is between 55 – 63%, in both palynofacies the percentage of phytoclast is low to moderate ranges change from 7 – 19, and 3-35% respectively. Paleodepotional environment of the Garagu Formation is oxic shelf (V, VIII). The Sarmord Formation is represented by palynofacies five (PF.5), this palynofacies is characterized by high percentage of phytoclasts which reaches to 74%, with moderate palynomorphs and amorphous organic matter ranges between 11 – 31%, 12 – 38% respectively. Shelf to basin transition (IV) is the claimed environment for the Sarmord Formation. Qamchuqa Formation is represented by palynofacies six (PF.6), this facies is also high percentage of phytoclasts content but more than PF.5, which the range is 48 – 85% with a moderate percentage of palynomorphs (12 – 43%) and a low percentage of amorphous organic matter (3 – 15%). The Qamchuqa Formation was deposited under proximal oxic shelf (III) condition.

Petrophysical properties of the Early Cretaceous Sarmord and Garagu formations from the Atrush and Sarsang Blocks in the Kurdistan Region are studied. These formations are generally composed of limestones and dolomitic limestones interbedded with thin to medium layers of yellowish-gray marl (calcareous mudstone). The current study shows that the average shale volume in the Sarmord and Garage formations is between 16% and 20%. In Atrush-1 Well, the average porosity ratio of the Sarmord and Garagu formations is fair to good (15% and 11%, respectively). However, in Mangesh-1 Well, the porosity value is poor; it is around 4% on average. Generally, most of the hydrocarbons that have been observed within the pore spaces are residual oil type in Atrush-1 Well and movable hydrocarbon type in Mangesh-1 Well. In Atrush-1 Well, out of 362 m thickness of both formations, only 180 m is considered to be a pay zone; whereas, the pay zone is just around 8.0 m thick out of 347 m of the total thickness. According to the calculated porosity values, the Garagu and Sarmord formations are not considered as good reservoirs in the studied wells, with the exception of Atrush-1 Well where the Sarmord Formation has fair potential reservoir characteristics.