In order to investigate the controlling mechanism of temperature,fluid and other factors on water-rock interaction in the diagenetic process,we performed a series of simulated experiments on the interaction between two kinds of fluids with different salinity and a composite mineral system(simulated sandstone),which contains albite,K-feldspar and other minerals.The experimental results showed that acidity was the most important factor that affected the dissolution of minerals in the composite mineral system.The lower the pH value,the more easily the minerals dissolved.At the same pH value,the dissolution abilities of different acids for various mineral components were also different.Compared to hydrochloric acid(inorganic acid),oxalic acid(organic acid) was more able to dissolve aluminosilicate minerals.However,the dissolution ability of oxalic acid for carbonate minerals was lower than that of hydrochloric acid.In the process of fluid-rock interaction,dissolution of feldspar was relatively complicated.Increase of temperature would accelerate the dissolution of feldspar.Under acidic conditions,albite had a higher dissolution rate than K-feldspar.K-feldspar could dissolve and convert into montmorillonite and kaolinite,while albite could dissolve and convert into kaolinite both at 40°C and 80°C.Presence of organic acid,and decrease of pH value and water salinity were all favorable for the dissolution of feldspar,but weakened the ability to form clay minerals.
The concept and division method for petroleum accumulation system,based on layer structure,are presented according to characteristics of layer structure and reservoirs. The petroleum accumulation system of Jiyang depression can be divided into four levels,namely petroleum accumulation system combination,petroleum accumulation system,oil-gas reservoir combination and reservoir. The petro-leum accumulation system combination includes three types of genetic pattern: other-source bur-ied-ridge accumulation system combination in pre-Paleogene,medium-deep layer self-source accu-mulation system combination in Paleogene,and shallow layer other-source accumulation system combination in Neogene. This paper also describes the reservoir types and their distribution charac-teristics of different petroleum accumulation system combinations and their interior units.
XU HuaiMin1,XU ZhaoHui1,ZHANG ShanWen2,WANG ZhiGao2 & WANG YongShi2 1 Faculty of Resource and Information Technology,China University of Petroleum,Beijing 102249,China
Hydrocarbon resources in low-permeability sandstones are very abundant and are extensively distributed. Low-permeability reservoirs show several unique characteristics,including lack of a defi nite trap boundary or caprock,limited buoyancy effect,complex oil-gas-water distribution,without obvious oil-gas-water interfaces,and relatively low oil(gas) saturation. Based on the simulation experiments of oil accumulation in low-permeability sandstone(oil displacing water) ,we study the migration and accumulation characteristics of non-Darcy oil flow,and discuss the values and influencing factors of relative permeability which is a key parameter characterizing oil migration and accumulation in low-permeability sandstone. The results indicate that:1) Oil migration(oil displacing water) in lowpermeability sandstone shows non-Darcy percolation characteristics,and there is a threshold pressure gradient during oil migration and accumulation,which has a good negative correlation with permeability and apparent fluidity;2) With decrease of permeability and apparent fluidity and increase of fluid viscosity,the percolation curve is closer to the pressure gradient axis and the threshold pressure gradient increases. When the apparent fluidity is more than 1.0,the percolation curve shows modifi ed Darcy flow characteristics,while when the apparent fluidity is less than 1.0,the percolation curve is a "concaveup" non-Darcy percolation curve;3) Oil-water two-phase relative permeability is affected by core permeability,fluid viscosity,apparent fluidity,and injection drive force;4) The oil saturation of lowpermeability sandstone reservoirs is mostly within 35%-60%,and the oil saturation also has a good positive correlation with the permeability and apparent fluidity.
