A Novel Well Treatment Method Based on In-Situ Hydrolysis and Flocculation of Inorganic Compounds
Authors: Lakatos I. , Lakatos-Szabo J. , Kristof M. , Kosztin B. 
Published: December 2007

Application of conventional profile correction techniques is often limited by incompatibility of chemicals with low permeable porous media, non-selective placement of treating fluids and poor thermal stability of blocking phases. Theoretically, these problems might be cured mostly using low molecular weight inorganic compounds and low viscosity particulate solutions. Development of a new well treatment method was stimulated by recognizing that some inorganic compounds of transition metals can be transformed directly or indirectly into gel-like precipitate by in-situ hydrolysis which is then immobilized by in-situ flocculation or spontaneous ageing. The laboratory studies were extended to Fe(III), Al(III) and Cr(III) compounds, while alkaline materials and low molecular weight polyacrylamides were used as hydrolyzing agents and flocculants, respectively. It was definitely proved that the novel technique is an effective method for permanent permeability reduction even in porous systems having high permeability &gt;5 m2) and the spontaneous ageing (aggregation) of gel particles leads to first immobilization of the injected fluids. The blocking materials, particularly Fe(III) hydroxide and oxy-hydroxide gels, have excellent thermal stability &gt;150 C), but in case of technological failure the gel phase can easily be broken up into mobile Graham's sols. Further, the method is characterized by outstanding placement selectivity, self-controlling (spontaneous) chemical mechanism and injectivity problems may not arise even in low permeable (&lt;0.05 m2) porous systems. At the present time the method is positively tested at the largest Hungarian oil field.

Introduction

Converging field experiences unequivocally prove that profile correction in layered or highly heterogeneous systems with limited cross-flow influences significantly the displacement mechanism and results in a substantial surplus oil production. During the past decades the well stimulations of that type has shown outstanding records in practice and that fact accelerated not only the R&D activity but also the field pilots and routine applications. A great variety of chemicals and diverse chemical principles were used and elaborated to develop appropriate procedures and accordingly, numerous new terms became regular in production engineering. Although the names like "blocking", "sealing", "profile correction", "water shut-off" plastically characterises the final goals, non of them covers the complex chemical and reservoir engineering mechanism which finally leads to enhanced oil production. Therefore, it seems difficult to classify the different methods meanwhile it is necessary to make some grouping. Principle of grouping might be the chemical reaction mechanism, the chemicals applied or the blocking (flow, rheological) mechanism forming the basis of the reservoir engineering concept.

The idea of water shut-off treatments raised as early as the middle of the sixties. Since that time a great variety of so-called polymer methods have been developed forming three main groups: injection of polymer solution, in-situ cross-linking of chain like polymers and in-situ polymerization of monomers. Their general feature is that they are based on application of macromolecular materials. Such a common denominator can not be found as far the blocking mechanism is concerned. Since the philosophy of profile correction methods is that a deliberate formation damage or a drastic mobility reducing effect must be developed in a right reservoir space the techniques, in a wider sense, can be classified as follows:

Mobility control by modification of rheological properties–Injection of polymer solutions–In-situ cross-linking of linear polymer–In-situ polymerization of monomers–Combined, multifunctional method–Precipitation of gel-like inorganic compounds–Precipitation of crystalline inorganic compounds

Mobility control by modification of pore structure

P. 337