Abstract. The prediction of permeability in tight carbonate reservoirs presents ever more of 8 a challenge in the hydrocarbon industry today. It is the aim of this paper to ascertain which 9 models have the capacity to predict permeability reliably in tight carbonates, and to develop a 10 new one, if required. This paper presents (i) the results of laboratory Klinkenberg-corrected 11 pulse decay measurements of carbonates with permeabilities in the range 65 nD to 0.7 mD, 12(ii) use of the data to assess the performance of 16 permeability prediction models, (iii) the 13 development of an improved prediction model for tight carbonate rocks, and (iv) its 14 validation using an independent data set. Initial measurements including porosity, of the models were developed especially for tight gas sands, while many were not. Critically, 21 none were developed for tight gas carbonates. Predictably then, the best prediction was carbonates, will lead to gross errors and that the development of new methods that are 33 specific to tight carbonates is unavoidable.

10In carbonate reservoir rocks the complex interaction between the petrophysical 11 properties corresponds to the various depositional microstructures which are modified 12 by various diagenetic processes that ultimately define the reservoir quality, and pose permeability. Consequently, mineralogy is not a useful controlling factor for permeability. 3Diagenetic processes have altered the depositional texture significantly, resulting in 4 changes to the pore size and pore-throat size distribution and affecting the permeability. 5In addition the matrix permeability is sensitive to stress, with permeability decreases 6 between -410 -4 mD/psi and -410 -5 mD/psi in the effective stress range from 0 psi to 7 4000 psi. It has been found that of the three microstructure pore types the nano-8 intercrystalline pore system is more sensitive to increasing effective stress compared to

The Lower Miocene Euphrates and Jeribe formations are considered as the main targets of the Tertiary petroleum system in the western part of the Zagros Basin. The formations consist of carbonates with some evaporate intercalations of the Dhiban Formation. This study utilized data from a field investigation including newly described outcrop sections, newly discovered productive oil fields within the Kirkuk embayment zone of the Zagros Fold and Thrust belt such as Sarqala and Kurdamir wells. This work is the first to show a stratigraphic correlation and palaeoenvironmental interpretation by investigating both well data and new outcrop data. Three depositional environments were identified, an: 1. Inner and outer ramp belts environment; 2. shoal environment; and 3. restricted lagoon environment.Within these three environments twelve microfacies were identified, based on the distribution of fauna mainly benthonic foraminifera, rock textures and sedimentary structures. The inferred shallow water depths and variable salinities in both the Euphrates Formation and Jeribe formation carbonates are consistent with deposition on the inner ramp (restricted lagoon and shoal) environments. Those found in the Euphrates Formation constrained the depositional environment to the restricted lagoon and shoal environment, whilst the microfacies in the Jeribe Formation provided evidence for an inner ramp and middle to outer ramp belt environments. This study represents the first detailed research that focuses on the stratigraphic correlation and changes in carbonate facies with the main aim to provide a wider understanding of stratigraphy of these carbonate reservoirs throughout the northern part of Iraq.

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This is a repository copy of Developing pore size distribution models in heterogeneous carbonates using especially nuclear magnetic resonance.