Influence of sedimentary facies on reservoir quality and distribution of diagenetic features in the Funing Formation,Wanglongzhuang Oilfield,Subei Basin,Eastern China

The Paleogene clastic sediments of the Funing Formation, which is characterized by slump-fan, delta-front, and beach-bar deposits, are important targets for oil and gas exploration in the Wanglongzhuang Oilfield, Subei Basin, eastern China. Three categories of reservoir quality are distinguished on the basis of petrographic and petrophysical experiments such as nuclear magnetic resonance (NMR) and mercury injection (MI). A paragenetic sequence for diagenetic evolution of each sedimentary facies has been reconstructed to determine the mechanisms for the variations in reservoir quality of the formation and the influence of the sedimentary facies on the distribution of diagenetic features in each of its members. The maturity of the organic material, textural relationships, and the distribution pattern of diagenetic minerals suggest that the study area underwent mainly mesodiagenesis. The mesodiagenesis A and mesodiagenesis B stages induced different diagenetic features in the target reservoir; the beach-bar sand of the E₁f₂ unit and the delta-front sand of the E₁f₄ unit underwent mostly only cementation; the delta-front deposits of the E₁f₃ unit, however, suffered more from mechanical and chemical compaction than from cementation. The loss of porosity in the fluxoturbidites of E₁f₄ due to compaction was just as large as the loss by cementation. The gravity-flow channel, sand-bar, and distributary-channel deposits have a higher porosity and permeability than the sand-beach and estuarine-bar deposits.