Pore Structure of Low Permeability Sand Rock and Fluid Flowing Characteristics
|Course||Mineral prospecting and exploration|
|Keywords||Low permeability reservoir Pore structure Wettability Oil and water flowing mechanism Oil and water relative permeability|
It is very significant to research the pore structure and fluid flowing in low permeability porous media because the flowing in low permeability reservoirs is different from high-middle permeability reservoirs. The pore structures of ten oil and gas rock layers in different oil fields have been studied completely. This paper has also researched the surface characteristics of low permeability rock, the reason of oil-wet property in low permeability rocks, the oil and water flowing in weak oil-wet low permeability porous media and the factors affecting on oil and water flowing by use of sand micro-models and core experiments. The results are as follows:1. The degree of diagenesis, the composition packed in pore, the contact association between particles and pore type are the important factors affecting on the pore structure of low permeability rocks, and the permeability of low permeability rocks has the relation to the porosity positively.2. Mercury capillary cures have complicated shapes. Thus the pore distribution is commonly double or multi-peaks distribution. The pore structure parameters are some related to rock permeability and porosity, and some parameters have connection with one another. The structure flowing coefficient is brought forward for expressing affecting ability of pore structure on fluid flowing. Based on the structure flowing coefficient, low permeability rocks are divided into four kinds, that is, Ⅰ type of pore structure rocks, its permeability is more than 1.6×10-3μm2, is general low permeability reservoir;Ⅱ type of pore structure rocks, its permeability is 1.6-0.8×10-3μm2, is lower permeability reservoir;Ⅲ type of pore structure rocks, its permeability is 0.8-0.3×10-3μm2, is super-low permeability reservoirs;Ⅳ type of pore structure rocks, its permeability is less than 0.3 ×10-3μm2, is dense low permeability reservoirs.3. The rock of low permeability reservoirs has rough and complicated surfaces, and its surface area is larger and more electric, and of hydrophilic property. The weak water-wet minerals and the polar substances absorbed on rock surface will make the surface of low permeability rock oil wet.4. The oil and water distribution and flowing in weak oil-wet low permeability rock are different water-wet rock, and oil phase can flow on rock surface spontaneously. It is not the main factor affecting on displacing oil efficiency, and the pore structure is the main factor of influence on displacing oil efficiency.5. There is the important influence of wettability on oil and water relative permeability curve of low permeability cores, and it is very different from high-middle permeability cores. The permeability and micro-fracture are the primary factors affecting on the curve shape of the relative permeability of low permeability cores, and their influence is very various because of the different wettbility.These results are very important to valuate low permeability reservoirs and realize the oil and water flowing mechanism through low permeability pore media on theory.