Characteristics and genesis of carbonate reservoirs in the Mishrif MB₂¹ member in the Missan oil fields, Iraq

The characteristics and genesis of carbonate reservoirs in the Mishrif MB₂¹ member in the Missan oil fields were studied based on core, well logging, seismic and production data. The reservoirs were mainly deposited in a carbonate open platform sedimentary environment, and developed several subfacies such as bioclastic shoals, bioherms and open subtidal deposits. Rudist grainstones, skeletal grainstones, skeletal peloidal grainstones and skeletal peloidal packstones were found. Primary intergranular pores, secondary dissolution pores, mouldic pores, micro-pores associated with matrix, a small quantity of micro-vuggy and micro-fractures provided space for hydrocarbon accumulation. Controlled by deposition and diagenesis, reservoir distribution was similar laterally, but varied obviously vertically and showed a strong heterogeneity, which restricted oil development.