Factors Influencing the Deterioration of s Plastic Sand Consolidation Treatments

Abstract

Plastics, such as epoxy, that have good wetting and adhesive properties, Plastics, such as epoxy, that have good wetting and adhesive properties, that produce no reaction by-products, and that undergo minimal shrinkage during cure, appear to be the best suited for use in sand consolidation. Introduction Sand production from poorly consolidated reservoirs has long presented a very troublesome and costly problem to the oil industry. Many millions of dollars problem to the oil industry. Many millions of dollars are spent each year to control or dispose of produced sand. Furthermore, the problem is more acute now than it has been at any time in the past because increased production rates have led to increased stresses on the formation. This not only increases the likelihood of sand production, but at the same time it makes sand more difficult to control. Unfortunately, this trend is likely to continue as production rates are increased even further to meet the continuing rise in the demand for energy. One extensively used method of controlling sand production consists of strengthening, or consolidatng, production consists of strengthening, or consolidatng, the near-wellbore region with plastics. This is accomplished by injecting liquid chemicals into the formation immediately surrounding the perforated interval. These chemicals then harden to form a plastic that coats the individual sand grains of the invaded region, bonds them together at their points of contact, but leaves the pore spaces open and interconnected to retain permeability. This technique has proved quite effective and has been found to offer several advantages over other sand mitigation methods. As a result, a number of consolidation systems (almost all employing thermosetting plastics from the phenolic, furan, or epoxy families) have been developed and thousands of consolidation treatments have been carried out since the first job was performed more than 25 years ago. In spite of this success, none of the currently available sand consolidation systems provides a completely permanent solution to the sand problem; many of the originally successful jobs eventually fail before the reservoir is depleted. This is costly, not only in terms of workover expense, but also in terms of interim production losses. As a result, there is considerable incentive to develop consolidation techniques that are more permanent. The purpose of this study was to determine why initially successful treatments fail, in the hope that this information would provide direction for the development of more durable techniques. The study revealed that failure is due both to incomplete coating of some sand grains and to subsequent deterioration of the plastic with coated grains that in time causes the consolidated region to lose strength. Further, it was determined that this deterioration was due predominantly to cohesive failure of the plastic, predominantly to cohesive failure of the plastic, followed by adhesive failure at the plastic/sand interface. Cohesive failure was observed to be accelerated by physical and chemical properties common to some thermosetting plastics. At first these studies were concentrated on a consolidation process that employs a phenolic plastic. Many of the conclusions of this work were derived from studies of that system. JPT P. 157