Permeability Study And Application In A Certain Oilfield In Bohai

Since there were some problems when using the permeability formula at OIP stage in a certain oilfield in Bohai, the permeability of this oilfield in Dongying Formation had been restudied, combined with its production performance data. Two new methods to calculate the permeability had been presented in this paper, which had been applied and testified in this oilfield, and achieved excellent results.OIP permeability data were got according to the relativity between porosity with permeability, between GR with core grains. Using core lab data, physical properties were calculated by multi-mineral model. This way was examined strictly and calibrated with core lab data in OIP stage. It is fit to evaluation of reserves of a new oilfield.On oilfield development stage, horizontal and vertical anisotropy became obvious with increasing of the well number and oilfield's area. Consistence between OIP permeability with dynamic data isn't enough good. There are mainly three reasons.Firstly, Porosity and permeability regression is so simple that the result data has no good accuracy. Although pore structure determines permeability in oil layers, porosity isn't equal to permeability. There is intrinsic defect in this way. It doesn't have excellent representation.Secondly, OIP multi-mineral model isn't fit for oil base wells. There are obvious differences between oil-base wells with water-base wells. Rxo measured is high abnormally in oil-base well. If this Rxo is used to calculate porosity and shale volume in OIP multi-mineral model, shale volume will be higher and porosity will be lower than they should be. At last, lower porosity causes lower permeability. Thirdly, Relativity between oil saturation with permeability doesn't be considered. By capillary pressure curves, oil saturation can be got indirectly from the consistence among fluid characters and oil column height and capillary pressure, after the conversion of Hg-Air wetting phase and reservoir-lab parameters such as pressure. So we can cognize that oil saturation can identify permeability in certain oil layer in the same oilfield. This rule almost exists in all of the oil layers after a number of wells'analyses. On OIP stage, resistivity isn't considered, but high oil-saturation wells always have better production, which causes lower permeability than they should be.Formation physical properties'calculation in oil base wells. If current oil base well were water base, there is a Rxo curve which can be input OIP multi-mineral model to get proper results. So, we can rebuild one Rxo curve by the Rxo curves of the water base wells surrounding the current oil base well. Then we can get what we want by the rebuilt Rxo and other curves. After finishing this step, I have set up two new ways to calculate permeability. One method is named as CM classification. It's based on the facies study and CM grain size analysis, which had been used to class the reservoir formation as A and B. A corresponds to under-water distributary channel and mouth bar microfacies, mainly with coarse, medium and fine sand. B corresponds to interdistributary channel area microfacies, mainly with very find and silt sand. According to A and B classifications, permeability formulas had been regressed respectively. The other is multiple regression including resistivity, porosity and shale content. Since there is relationship between permeability, capillary pressure, pore structure and oil saturation, for oil pay zone, its resistivity had been considered as an important unit to regress the permeability formula. Similarly, we got permeability formulas for wet zones by intervals.Recalculated permeability has better accuracy and consistence with dynamic data macroscopically. Recalculated permeability has been used in geological model building, reservoir fine description and oil field adjustment for about one year, and has satisfying effect. Considering the theory, operation, and practice in current oilfield, both of the two ways can be spread out.