Research On Production Decline Theory And Model-building In High Water Cut Reservoirs

When the oil field goes into the high water cut stage, it becomes more and more difficult to control the oil output. At present, researching on discipline and characteristics of production decline, grasping operation rules of the high water cut reservoir accurately become the main issues. Through looking up plenty of document information, many problems of present production decline are studied in this paper. For tackling existing problems, analytical model, semi-analytical model and multi-factor descending model, which are applied to high water cut field, are established. On the basis of theoretical analysis and instance validation, it comes to the results as follows:Investigate theoretical principle of production decline regularities. It provides theoretical support for future production decline study. And it receives main factors by comparative analysis. Analytical model is established by improving relative permeability curve and integrating reservoir engineering approach and infiltration theory. And it calculates the effect of relative permeability curve, viscosity ratio of oil and water, oil recovery rate and fluid recovery rate on natural declining rate. Finally a series of figure plates are achieved.Propose a new water drive characteristic curve. And it will have great significance to research water-drive reservoir in the future. Applying above new water drive characteristic curve and fluid productivity index and oil productivity index, semi-analytical model is proposed. It analyzes the effect of relative permeability curve, viscosity ratio of oil and water, constant oil recovery rate of recoverable reserves and constant fluid recovery rate on natural declining rate. Calculation method of semi-analytical model and a series of figure plates of nature decline rate are given. It has very high applicability because of reservoir geological factors, fluid factors, develop factors.Establish numerical model of high water cut reservoir. Analyze the effect of water-cut stage, fluid production rate, relative permeability curve, viscosity ratio of oil and water, homogeneity degree, damage condition of well pattern, the type of well pattern and well spacing on natural declining rate. Carry out tentative designs and multi-factor sensitivity analysis for above factors. The simulation results during high water cut stage are in general agreement with corresponding analytical model and semi-analytical model. Establish multi-factor descending model of natural declining rate. The regularities between production decline rate and these factors are achieved, so it is easy to carry out qualitative and quantitative analysis to natural production rate of different reservoir. The results are in accordance with practical situation basically by example verification.This paper obtains production decline law theoretical basis, analytical model, semi-analytical model and multi-factor descending model adequate for actual production. It improves present declining regularity theories and research approaches. In a word, the research results are valuable for theoretical studies of production decline and actual production in high water cut reservoir.