水産養殖研究開発ジャーナル

概要

Porosity and Permeability Analysis from Well Logs and Core in Fracture, Vugy and Intercrystalline Carbonate Reservoirs

Qays Mohammed Sadeq *,Wan Ismail Bin Wan Yusoff

The 60% of the world's oil and 40% of the world's gas reserves occurs in carbonate reservoirs. Around 70% of oil and 90% of gas reserves held within the carbonate reservoirs in the Middle East for example. Carbonates can exhibit highly varying properties (e.g., porosity, permeability, flow mechanisms) within small sections of the reservoir, making them difficult to characterize. A focused approach is needed to better understand the heterogeneous nature of the rock containing the fluids and the flow properties within the porous and often fractured formations. This involves detailed understanding of the fluids saturation, pore-size distribution, permeability, rock texture, reservoir rock type, and natural fracture systems at different scales. Deposition, sedimentation, diagenesis and other geological features of carbonate rocks has been studied leading their classification into: mudstone, wackestone, packstone, grainstone, boundstone and crystalline carbonate rocks. Various features such as fractures and vugs, which influence its petrophysical behavior, characterize all these. The study of the main features of carbonate reservoir using Archie’s cementation exponent “m” is an acceptable method of verifying the geological features in the reservoir, which actually contribute to rock fluid properties and other production attributes of the reservoir. This proved for some reservoir using well log values for KF2 oil field in Iraq. The dominating geological features of the field confirmed from a graphical representation of the different data from field reservoir. The reservoirs used as case studies in the research classified into different carbonate rocks using a graphical plot of their permeability against porosity values. This result gives an evidence of the textural and grain size characteristics as well as the effective pore sizes of the reservoir. This method of analysis makes it easier to evaluate the post diagenetic strength of the reservoir rocks and fluid hosting capability in assessment of recovering.