Research On Comprehensive Evaluation Method For Low Permeability Reservoir

The exploitation of low permeability reservoirs in Daqing and Changqing tells that there is a great disparity in exploitation difficulty and effect, although the lateral permeability is similar. The active reservoir classification and standard system focus on the key factors of permeability, which adds uncertainty to the developing policy and construction programming. So, it is necessary to do more research on how to classify the reservoirs.Firstly, the paper demonstrates the necessity of the low permeability reservoirs' analysis factors that include main throat radius, movable fluid saturation, and starting pressure gradient, then the contents and types of clay and the viscosity of underground crude oil added in. All above build up the system of low permeability reservoirs' analysis factors.Following the single kind of factor range, the analysis for certain factor gotten from low permeability reservoirs in Daqing and Changqing shows that the factor is unsteady. In this condition, fuzzy mathematical comprehensive evaluation on low permeability reservoirs, which is based on fuzzy mathematics, is in use. First of all, with the comparison between advantages and disadvantages of both membership function and conventional method of deciding weight, the analysis hierarchy process(AHP) calculates various percentages of five factors, then the variable weight theory solves the lack of sector analysis factors. According to the integrative analysis value, the low permeability reservoirs are separated into four kinds: the first and the second can be effectively developed under the actual technology; the third is the reservoir that scientists do research on; the forth is undiscovered.With fuzzy integrative analysis system mentioned above, all analysis and comparison results gotten from low permeability reservoirs in Daqing and Changqing show that the permeability of low permeability reservoir in Daqing is much higher than the ones in Changqing, when the reservoirs are of the same kind. The analysis and actual developing results of single well and the whole section in Changqing prove that the high integrative analysis value means high single well production. The same method works in the super-low permeability reservoir in Changqing. The reservoirs with 0.3md in Changqing is the floor level of the second kind mentioned above or the third ones whose integrative value is lower than 0.6. It is significant for making clear the target reservoir in Changqing oil field.The intellective analysis system for low permeability reservoir, which is based on nerve cell network, has been made into software. The software takes the 7 sections in Changqing as examples for intellective training, and establishes the relationship between analysis factor and single production index. The production prediction under the nerve cell network is almost equal to the oil extraction strength of a single well. The prediction of single production ability for the 9 sections in Changqing offers valuable references for the future development and investment.