Consolidation of Silty Sands with an Epoxy Resin Overflush Process

Abstract

This epoxy resin system for consolidating loose sand around a wellbore can be used in the temperature range of 100 degrees to 220 degrees F and is effective on both clean sand and argillaceous sand. An added advantage of the process is that it results in very little loss of well productivity. productivity. Introduction A phase-separating epoxy resin process for consolidating sand in oil wells was developed in 1958, and since that time more than 1,000 wells have been treated. The consolidation is effected in a zone extending 2 to 3 ft radially around the borehole. The sequence of steps involves first flushing all crude oil and water from the zone to be consolidated, then filling the pore space with a dilute single-phase resin solution, and finally allowing this solution to remain stationary in the formation until polymerization of the resin is complete. During polymerization of the resin is complete. During the polymerization step, a relatively concentrated resin phase separates, preferentially wets the sand, collects in the pendular spaces, forms a strong bond with the sand grains and hardens. The result is the consolidation of a mass of sand or formation with relatively little loss of permeability, since most of the resin is at grain-to-grain contacts. This method of sand control has been successfully applied in many unconsolidated or friable sandstone formations. However, extensive laboratory and field tests show that this process does not effectively consolidate very fine-grained, silty, and argillaceous sands. Therefore a laboratory investigation was directed toward the basic cause or causes of this limitation. The results of the study show that adsorption of the amine curing agent or poor wetting of the clay minerals by the resin was not responsible for the low compressive strength, nor was the difficulty due to failure of the alcohol preflush to remove water from the clay. The presence of clay or fine particles greatly increases the fraction of total pore space present in tiny capillaries or pendular space. It was concluded that these pore spaces must be completely filled with resin before pore spaces must be completely filled with resin before a significant amount of resin can accumulate in the larger grain-to-grain weight-bearing contacts. Resin must be present in these contacts to produce consolidation. Actual measurements of the amount of resin required to fill this tiny capillary space and inspection of typical capillary pressure curves showed that two to three times as much resin (Fig. 1 and Table 2) would be required as can be supplied by the phase-separating resin technique. The new process (an overflush method) described here was developed to supply this increased resin requirement when needed, and yet make it possible to consolidate clean sand without excessive loss of permeability. Presented here is a study of the physical chemistry of the overflush system and the mechanism by which the process achieves consolidation in both clean and shaly sandstones. The chemistry of the various reactions is not considered here, as it is adequately covered in several textbooks. (A discussion of the more pertinent factors related to field applications of epoxy pertinent factors related to field applications of epoxy resins can be found in Ref. 6.) General Description of the New Process Preflush Preflush As with other epoxy sand consolidation systems, it is necessary first to remove formation fluids from the sand to be treated. P. 1103