Study On The Characteristics Of The Micro-pore Structure And The Comprehensive Reservoir Evaluation Method For The Low Permeability Carbonate Reservoir In One Typical Oil Field

The low permeability carbonate reservoir is one of the most important reservoirs type among the CNPC’s overseas oilfield. Due to the low permeability carbonate reservoirs’ complex pore structures, the characteristics of the low permeability carbonate reservoir vary a lot with the sandstone reservoirs. In this case, the evaluation research study for the low permeability carbonate reservoir is urgently needed. Combining with some experiments, such as constant pressure mercury, nuclear magnetic resonance (NMR) and physical simulation, the paper analyses the micro pore structure and the moveable fluid of the different low permeability carbonate reservoirs of A oil field. Then, the low permeability carbonate reservoirs’complex pore structures is thoroughly studied by the nuclear magnetic resonance and the whole core CT-scanning analysis technology. The main research results are summarized as follows:1.Throat distribution, pore-throat ratio are the main factors that control reservoirs properties. The low permeability carbonate reservoir’s throat radius is smaller than the sandstone and the pore path is larger than the sandstone, when the permeability is near. The pore path radius ’peak value vary little but the distribution range change obviously and The throat radius vary much as the carbonate’s permeability vary. The relationship between the average throat radius, the pore-throat ratio and the permeability are power function relationship.2.NMR testing result shows, for the low permeability carbonate reservoir, the T2 relaxation pectrum mostly have one peak and the peak value is larger than the sandstone. The moveable fluid become lager as the permeability increases, and their correlation gets better as the permeability increases. The heterogeneous medium degree is more apparently as the permeability decreases.3.Combining the full diameter core scanning technology with the NMR test, a new method of measuring the carbonate reservoir’s pore types is put forward. The T2cutoff time of the fracture type is between 10-1000ms, The T2 cutoff time of the corrosion hole type is between 1-1000ms,and the pore type is between-100ms.4.The experiments of starting pressure gradient testing result shows, the same permeability level, the starting pressure gradient decreases as the permeability increases. The starting pressure shows a good correlation with the permeability. It’s an important reservoirs evaluation index.5.Considering the water and the oil movable ability in the rock space, calculate the largest movable flow ability, and determine the difficulty of exploit in different reservoirs.6.Basing on the reservoirs characters of the low carbonate reservoirs in this paper, combining the traditional permeability-pore evaluation standard, the evaluating method for the low carbonate reservoir is established and has been taken on the low carbonate reservoirs of A oil field.