Interwell dynamic connectivity is one of the important indicators for development evaluation of water flooding oilfields. It is widely used in identification of dominant channels, judgement of fracture sealing and evaluation of development effect. The traditional capacitance-resistance model (CRM) can not consider the change of start-up pressure gradient and liquid production index of heavy oil reservoir. For better quantifying the interwell connectivity of heavy oil reservoir, a new method is proposed using performance data and intelligence algorithm.
Experiments show that there is a starting pressure gradient in heavy oil flow. The pseudo-start pressure gradient model is used to characterize this phenomenon. On this basis, the fluid production model of heavy oil reservoir is deduced and established. The results show that the liquid yield index increases with the increase of water content, which is not a constant. And then, a time constant function is constructed to characterize the lag and attenuation of water flooding signals in formation propagation. By substituting the production model and the time constant function into the equation of material balance, a new model is established by difference method. The solution of the new model is transformed into an optimization problem by using the least squares principle. And the quantitative connectivity evaluation is obtained by using frog leaping algorithm.
The new model has been applied in many oilfields. Compared with the single-well dynamic analysis, the accuracy of the new model is very high, but the spent time is less than half of the single-well dynamic analysis. In addition, the paper presents a case study to compare findings from the results of the new model and the use of interwell tracer and interference well testing. The results obtained from this paper shows good agreement with the results obtained from interwell tracer or interference well testing. However, compared with the tracer test or interference well testing, the new method can save a lot of money. In summary, this paper is not only feasible, but also saves a lot of time and money.
The new method considers not only the starting pressure gradient of heavy oil, but also the change of liquid production index. It is an effective method for evaluating injection-production connectivity.
