Interlayer Development Characteristics and Water Flooding Strategy Optimization in Porous Carbonate Reservoirs: A Case Study from the MC1-1 Sub-member in B Oilfield, Iraq

Carbonate reservoirs play an important role in global oil and gas industry, especially in the Middle East. As one of the main oil-bearing formations in B oilfield, sub-member MC1-1 is a relatively thin porous carbonate reservoir with strong heterogeneity, which reflects on the alternative appearance of interlayers and reservoirs vertically. As water flooding has been implemented in the oilfield, it is necessary to conduct in-depth study on the development characteristics of the interlayer and its influence on water flooding. In this study, the physical and distribution characteristics of the interlayers are investigated. Based on the well-logging results, statistical analysis is conducted on the frequence, thickness and physical properties of the interlayers drilled by the vertical wells. The results show that the interlayers are more developed in the northwest of the oilfield compared with the southeastern area on the plane, the average porosity of the interlayers is about 4.9%, and the average permeability of the interlayers is about 1.0mD. According to the test results of pressure measurement while drilling (PWD), the two sets of continuously developed interlayers are proven to have certain vertical seepage ability. Mechanism model is subsequently applied to match the vertical distribution of the formation pressure in each layer to divide the interlayers into three representative categories including strong-sealing, weak-sealing and non-sealing based on their vertical connectivity. Then water flooding strategies are optimized through integrated analysis depending on the reservoir and interlayer characteristics. The optimization suggestions put forward in this paper have been directly applied to the actual water flooding work in B oilfield, which has strong guiding significance for the oilfield development.