Diagenesis processes impact on the carbonate Mishrif quality in Ratawi oilfield, southern Iraq
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ORIGINAL ARTICLE
Diagenesis processes impact on the carbonate Mishrif quality in Ratawi oilfield, southern Iraq Hussein A. Chafeet1 · Maysaa Kh. Raheem2 · Nawfal A. Dahham1 Received: 2 April 2020 / Accepted: 14 June 2020 © Springer Nature Switzerland AG 2020
Abstract This paper aims to identify the impact of the diagenesis processes on the carbonate reservoir’s characteristics (porosity and permeability) of the Mishrif Formation. A detailed investigation of available core samples and microscopic study of more than 200 thin sections of the core limestone samples were examined from two wells (Ratawi-2 and Ratawi-5) in Ratawi oilfield, which are located in the Basrah Governorate, southern Iraq which revealed that different diagenetic parameters influence the reservoir quality in Mishrif Formation. Diagenetic features and four identified diagenetic environments that have affected the carbonate rocks in the Ratawi oilfield were the meteoric vadose, meteoric phreatic, marine phreatic and mixing zone. Petrographic examinations revealed that diagenesis varies in intensity from microfacies to another, micritization, dissolution, cementation, compaction, neomorphism, dolomitization and authigenic minerals (pyrite) are the dominant diagenetic parameters which are identified in the current field of study. Among all the observed diagenetic features, dissolution and neomorphism (recrystallization) were formed as a result of subaerial exposure during the meteoric diagenesis and contribute to porosity enhancement and reservoir quality. The cementation (calcite and dolomite), compaction, dolomitization, and micritization have a negative impact on the reservoir behavior, through reducing porosity and permeability that led to reducing reservoir quality. Other processes such as authigenic minerals (pyrite) did not have strong effects on reservoir quality. Based on the genetic classification of porosity, most of the porosity within Mishrif Formation is a combination of depositional, diagenetic and fracturing. The diagenetic porosity is the far more dominant types of porosity such as vuggy, intraparticles, fractured and moldic, implying that carbonate Mishrif reservoir is the type of diagenetic reservoirs. Keywords Diagenetic processes · Reservoir quality · Carbonate Mishrif · Ratawi oilfield
Introduction Diagenetic processes typically reduce porosity, redistribute the pore space, and alter permeability and capillary characteristics. Therefore, an understanding of diagenetic processes and the patterns of their products is essential for carbonate reservoir description and reservoir model construction * Hussein A. Chafeet [email protected] Maysaa Kh. Raheem [email protected] Nawfal A. Dahham [email protected] 1
Department of Oil and Gas Engineering, College of Oil and Gas Engineering, Basrah University for Oil and Gas, Basrah, Iraq
Basrah Oil Company, Ministry of Oil, Basrah, Iraq
2
(Lucia 2007). To understand the impact of the diagenesis processes and depositional environment on the carbonate reservoir prop
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