Field Evaluation of Iron Hydroxide Gel Treatments

Abstract

A novel gel treatment technique based on transformation of water soluble Fe(III) compounds into gel-like precipitate by in-situ hydrolysis and flocculation was developed for water shut-off in mature oil fields. The new blocking material has excellent stability under field conditions, and yet simple remediation is possible in case of placement failures. Further, the novel method is characterized by self-controlling chemical mechanism and using this technique injectivity problems didn't arise even in low-permeability and tough formations. The extensive field program was supported with special software determining the penetration distance from the wellbore. Based on log data, the pay zone was subdivided into a maximum of four layers assuming that crossflow among zones was negligible. Total volume of the treating fluids was obtained by asserting two limiting rules: the treating fluid must reach a minimum penetration depth (>15 m) in the layer having the highest permeability, but the max. penetration depth should not exceed 2 m in the layer having lowest permeability. The test program comprised treatment of ten oil producing wells and seven water injectors. The well responses varied between wide limits: technical success was achieved in about 60 % of the wells, and the treatment was economically beneficial in about 40 % of the cases. In special reservoir blocks the injector wells were simultaneously treated with the oil wells. The primary goal of this project was to enhance the effect of flow profile correction around the producers and to improve the frontal displacement mechanism. The new method was compatible with the dirty sandstone reservoir systems, and there were no technical failures. The positive results contributed significantly to the operator's decision to extend use of the new method to other reservoirs. 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. As far as the hydrocarbon industry is concerned, however, a real need to control flow profile around wells came to light only in the middle of the sixties. Since that time a great variety of polymer methodsusing polymer solutions, rigid and weak gels as diverting/blocking agents and disproportional permeability modifiers 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 and some earlier papers dealing with application of silicates1–4 and metal hydroxides5–9 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 polymer-based techniques.