Application of Iron-Hydroxide-Based Well Treatment Techniques at the Hungarian Oil Fields
Authors: Lakatos I. , Lakatos-Szabo J. , Kosztin B. , Palasthy Gy. , Kristof P. 
Published: December 2007

Abstract
Development of a new well treatment method was stimulated by recognizing that some inorganic compounds, particularly Fe(III) compounds, can be transformed into gel-like precipitate by in-situ hydrolysis which is then immobilized by in-situ flocculation or spontaneous aging. The blocking materials, have excellent stability under field conditions, but in case of technological failure the gel phase can easily be broken up into mobile sols. Further, the novel method is characterized by outstanding placement selectivity, self-controlling chemical mechanism and injectivity problems may not arise even in low permeable porous systems.
In frame of the field programme, extending over four years, 10 oil producing and 7 water injection well were treated. The well response were different: ration of the technical success was about 60 %, while 40 % of treatment was definitely profitable. In special reservoir blocks the injectors were simultaneously treated with the oil producing wells. The primary aim of this projects was to enhance the effect of profile correction around the producers and to improve the frontal displacement mechanism. The novel method proved to be compatible with the reservoir system and technical failure was not encountered during the past five years.
The positive results contributed significantly to a recent decision of the operator that, parallel with other profile correction and water-shut-off (e.g. polymer/silicate) techniques, application of the novel method will be extended to other reservoirs of the Algyö field, Hungary.

Introduction
The idea of water shut-off treatments raised already in 1922 when injection of silicate solutions into oil producing wells with the aim at gelation in-situ to form a blocking phase was patented. The barrier formation around the bore-holes was later developed exclusively on the basis of inorganic materials, but the different silicates were in the focus of grouting technologies used extensively in civil engineering. As far as the hydrocarbon industry is concerned, a real need to control flow profile came to light only in the middle of the sixties. Since that time a great variety of so-called polymer methods have been developed. Namely, application of inorganic compounds, if they were used at all, comprised mostly silicates neglecting other gel-forming substances. Therefore, the primary goal of this paper is to prove the feasibility, applicability and profitability of a novel well treatment method under field conditions which may represent an alternative solution, particularly in low permeable, tough reservoir systems where incompatibility problems may arise using the conventional techniques.

Principle of the Iron Hydroxide Based Method
In earlier papers1–4 it was mentioned several times that the reservoir engineering concept of profile correction, water shut-off, etc. is theoretically invariant to the factors whether the viscosity of fluids, pore structure or simultaneously both of them are modified in the target area. Surprisingly, however, the profile correction techniques based on application of inorganic compounds (except the silicates), particularly those which aimed at permeability lowering, were practically ignored until now. Therefore, the primary aim of the research project started some years ago was to evaluate the potential of such methods under laboratory and field conditions.