A Study on Micro-pore Structure and Infiltrating Mechanism of Chang-8 Reservoir in Qingyang Area Xifeng Oilfield
|Course||Oil and Gas Field Exploration and Development|
|Keywords||Xifeng Oilfield pore structure High pressure Hg injection rate-controlled Hg penetration diagenesis fluid mechanism micro-displacement experiment NMR|
With the employment of the techniques like cast thin slice, high pressure mercury intrusion, constant speed mercury intrusion, nuclear magnetic resonance, X-CT imaging technique, water/oil displacement experiment, mutual permeability and rock and mineral analysis, the thesis makes a thorough research into microscopic pore structure, filtration mechanism and influential factors of low permeability reservoir systematically and stresses on the study of the pore types, pore textures, the pore throat ratios, the removable fluid, the removable fluid saturation, the reservoir microscopes, the dynamic filtration characteristics, the water/oil displacement efficiency and the impact of sediment and diagenesis on these characteristics. The conclusions run as follows;The effective throat radius sizes of the low permeability reservoir get bigger with the width of the flow channels; the throat numbers increase with the numbers of flow channels. When the pore throats are fine, the individual pore is dominated by many big throats. Accordingly, the reservoir enjoys high permeability and the oil (gas) in the pores is easily recovered when flowing through the throats. When the pore throats are big, the individual pore is dominated by a few fine throats. Accordingly, the porosity communication is poor and some pores even become inactive pores or blind pores. The oil (gas) in the pores is hard to flow through the fine throats. As a result, the reservoir witnesses low recovery ratio.The results of oil/water displacement experiments and core CT scanning experiments demonstrate that oil/water displacement modes of the model mainly include the uniform patterns and the nonuniform patterns. The nonuniform patterns include finger-like displacement patterns and net-like displacement patterns. The uniform oil/water displacement enjoys high displacement efficiency. The low finger-like oil/water displacement efficiency is mainly caused by the inhomogeneity of the reservoir pore textures. The irreducible oil of the model mainly includes the oil film and the bypassing irreducible oil.The nuclear magnetic resonance (NMR) experiments demonstrate that the movable fluid saturation is low which is mainly caused by the fine throat radius.The Chang-8 low permeability reservoir in Qingyang area in Xifeng Oilfield witnesses low compositional maturity and texture maturity, high content of cement and fine grain grade, which are the main causes of the low porosity and the low permeability of the reservoir.With the increase of relative content of chlorite and the film thickness of chlorite that is attached on the pore walls, the permeability and the porosity decrease. Moreover, the values of permeability vary greatly, which shows that when chlorite cement blocks throats, the impact on the reservoir throats is larger than that on pores.Carbonate cement is a main contributor of the formation of the low permeability reservoir. Denudation that occurs among feldspar, debris and carbonate cement exerts positive impact on the improvement of reservoir physical property.