Abstract
Major oil producers in western Siberia widely use hydraulic fracturing to increase recovery from maturing reservoirs. Minimizing the quantity of produced water that typically accompanies increased hydrocarbon production is considered to be of the utmost importance. The traditional approach has been to limit well selection for fracturing treatments to candidates where stimulation can be efficiently performed without a subsequent increase of post-frac water cut. This significantly reduces the desired development of targeted fields.
In general, there are two main reasons for water production increase: (1) fracture propagation to water-saturated formations caused by the absence of reliable barriers and (2) phenomenon of water coning caused by pressure drawdown through a highly conductive fracture channel during the exploitation period. To mitigate the problem of post-stimulation water production increase, a relative permeability modifier (RPM) can be applied. The RPM itself is a polymer that can be pumped as a preflush to fracturing treatments or throughout the whole job. Under formation conditions, RPMs decrease the relative permeability of rock (reservoir) to water with almost no effect on the permeability of hydrocarbons. This is crucial to increase the oil-mobility ratio because it allows production of higher oil volumes without unacceptable quantities of associated water production.
Several fracturing job RPM treatments have been performed on different oilfields in western Siberia, and not all of them can be considered successful. Both satisfactory and unsatisfactory results were analyzed to classify the major groups of parameters that had the most impact on the final well performance. Based on this data, the candidate selection process for fracturing combined with RPM treatments for western Siberia oilfields should be improved to achieve more desirable treatment results. This paper contains guidelines to select the proper well for this type of treatment and, based on the case study, brings attention to different groups of parameters, related not only to formation properties but also to well preparation process and design criteria, that can significantly affect the final result.
