Abstract:

Water-bearing oil reservoirs generally occur in medium-low porosity and low-ultra low permeability clastic rocks and have the prominent characteristics of strong heterogeneity. Microscopically, clastic rocks have dual-pore structures, i.e. artesian pore throat system with the occurrence of liquid hydrocarbons and stagnant pore throat system saturated with original formation water. The artesian pore throat system contains artesian water, while the stagnant pore throat system mainly contains fine pore water, micropore water, stagnant pore water and molecular bound water. Stagnant pore throat system, accounting for a large proportion of pore volumes, would not only constrain production of oil and water, but also lead to the oil saturation of most water-bearing reservoirs to be below 50%. The geological conditions of formation of water-bearing reservoirs are related mainly to the structure of clastic rocks, extremely low compositional maturity and the poroperm characteristics drastically become poor due to compaction in the Mesozoic rift basin groups in Erlian. In the present economic and technical conditions, water-bearing oil reservoirs are still on the margin of commercial recovery, thus dynamic identification and evaluation of water-bearing oil reservoirs should be performed as early as possible according to oil-bearing condition of cores, water dropping test of cores, mud logging, thin-section analysis, poroperm analysis, mercury injection test, NMR and reservoir testing, so as to avoid ineffective investment.

Key words: clastic rock, dual porosity, water-bearing oil reservoir, formation, evaluation