COMPARISON OF PLOT ANALYTICAL METHODS FOR DETERMINING EXCESSIVE WATER PRODUCTION MECHANISMS IN OIL WELLS

Abstract

Watering of production wells is an important factor leading to a decrease in production profitability and an increase in costs. There are several main mechanisms of excess water inflow. These are a leak in the production casing; a violation of contact between the production casing and the rock; a formation of a bottom water cone; a raising the WOC surface to the perforation interval; a breakthrough through a layer with high permeability. Mechanisms can complement each other, forming a complex integrated system. To identify them, there are three groups of diagnostic methods — geophysical research, hydrodynamic well testing and plot analytical studies. Each of these fundamentally different groups can be supplemented by field research. Specifically in this work, we considered the latter. The analysis is carried out using the example of wells in one of the deposits of an oil field of the Arkhangelsk region. In which the causes of unwanted water production have already been studied by other methods and can be considered known. The studied reservoir is massive, with carbonate hydrophobic rocks and the reserves of the entire field are predominantly concentrated in it (97 %); the oil field (in terms of reserves) is small. There are no injection wells, operation is carried out in a natural elastic water drive mode. In the article, in total, three plot analytical methods are analyzed, which are among the main ones and have different application algorithms. Both the physical principles of their application and their effectiveness in relation to specific oil field are considered. These are the methods of K. Chan; L.I. Merkulova and A.A. Ginzburg; R. Novotny. The first studies the dependence of the water-oil ratio and its derivative on time (WOR and WOR’(t)), is the most widely known and has a large number of modifications (however, here they are not considered in detail). The second is based on the study of the so-called «water-cut characteristics» (representing the dependence of the accumulated oil production vs accumulated liquid production during the water period of operation). It has more restrictions, but is also more comprehensive. The third is based on a comparison of the permeability properties of reservoirs that change during operation.