Characteristics of carbonate reservoirs in the Timan-Pechora Basin in Russia: The Trebs and Titov oil fields as examples

The Timan-Pechora Basin is a petroliferous basin in Russia. It is a composite basin of rift, passive margin, and foreland. From the Early Riphing to Early Carboniferous, a rift, passive margin, and shallow continental shelf developed in the basin. From the Late Carboniferous to Quaternary, the Ural orogeny and post-orogeny foreland developed. Three sets of carbonate reservoirs were formed in the basin, including the Lower Paleozoic, Lower-Upper Devonian (Frasnian-Famennian), and Carboniferous-Lower Permian. They were controlled by both sedimentary and diagenetic effects. Favorable sedimentary facies and unconformities controlled the distribution of effective reservoirs. Reservoir porosity includes primary pores and dissolution vugs formed by karst. Reservoir physical properties vary both horizontally and vertically. Generally, the formation 30-40 m below an unconformity is the most favorable reservoir position. The reservoirs have a strong heterogeneity, and are featured by low porosity and low permeability, which restricts hydrocarbon exploitation. Data from 12 carbonate reservoirs with a long development history in the study area were analyzed, confirming low recovery rates and low recovery levels.