The Research Of Identification Method Of High Capacity Channel In Water Flooding Oilfield During The Later Period

Injection water for developing the reservoir is the widest application of development manner and secondary production method at present. a long and high speed water injection makes the pore structure of reservoir change greatly; the effect of injecting water on reservoir pores and cements and the change on pressure and temperature in oil reservoirs cause the permeability of reservoir increase and the radius of pore throat also increase, thus forming the high and extra-high permeability zone, which is high capacity channel, the existence of high capacity channel not only intensifies the interlayer conflicts,makes the inefficient circulation of injection water, but also makes the implement of stimulation more difficult. The performance characteristics of poor efficiency and inefficient circulation of water flooding in oil field: low water injection pressure, low starting pressure of reservoir, high water injectivity index, faster water drive rate of oil reservoir, low water storage rate; much different water injection profile, the ratio of the thickness of strong water absorption layer and the total thickness of reservoir is far less than the ratio of the corresponding water absorption rate, low Injection pressure index and so on; so, the research of identification method of high capacity channel can be helpful to improve the effect of water flooding, enhance oil recovery and have a important practical guiding significance to the water shut-off and profile control.In this paper, we have mainly introduced four identification methods of high capacity channel:fuzzy recognition system, well test interpretation model, streamline model identification method and multiple linear regression method to predict inter-well connectivity.For fuzzy recognition method, first of all, calculating quantitatively the factor indices of affecting high capacity channel using membership function, and then researching and determining the change ranges of various factors, for normalizing evaluation indices and weight values, finally, possessing comprehensively all kinds of static and dynamic factor indices making use of the theory of fuzzy and establishing qualitatively the identification expert system model of high capacity channel.Identifying1whether the existence of the high capacity channel by well test interpretation model, we mainly calculate the pressure difference△p and its derivative d△p/df·t based on the measured pressure drop data disposal, and then taking the logarithm△p,d△p/df·t and t respectively, to map into a combined chart of double logarithmic differential pressure and its derivative according to the same size as the chart, then moving the measured curve on the chart, finally, identifying the existence of the high capacity channel based on if it can fit the double logarithmic curve of measured pressure drop with typical curve.For streamline method, we do research into the fluid flow field and the oil-water distribution through the establishment of flow field distribution of visualization in three-dimensional, and then revealing the existence and distribution of preferential channel and visually describing the flow direction and region of the subsurface fluid.For multiple linear regression, chapter five discusses briefly the unbalanced multiple linear regression, balanced multiple linear regression and ridge regression, the method mainly predict the inter-well connectivity by calculating the inter-well connectivity coefficient, its main advantages:production and injection rate is the most abundant and accessible data in any water flooding, we can easily obtain some valuable and useful information about the inter-well connectivity by the data analysis using a simple model, but the limitations of the method are:The MLR model is based on a strict assumption that all producer bottom hole pressures are constant during the assessment interval. For this method, if there is extended or frequent shut-in oil field, it still assumes all of the wells have been being in operation, it is difficult to obtain a constant bottom hole production pressure in a real reservoir, it is a real solution to the limitations by the combination of bottom hole pressure in the process of inference. At the same time, we have simply introduced the capacitance model; this method can be applied to the oil field with frequent and long time shut-in. considering the part natural production of oil field and also can identify the inter-well connectivity using the change of bottom hole pressure. But it still remains to do a further and deep research.