Electroless Nickel Sand Consolidation: Laboratory Studies of Cementation and Calculated Effect on Well Productivity
Authors: Torrest R.S. 
Published: December 2007

Abstract
The electroless consolidation of formation sand with the catalytic plating of nickel from aqueous solution provides a flexible alternative to "plastic" or resin sand consolidation in certain cases. A shut-in period (required for resin curing) is not needed, stronger bonding is achieved, and the consolidation is suitable for exposure to temperatures far beyond the range of plastic sand consolidations. The character of laboratory-consolidated cores is described, with emphasis on the permeability, porosity, and compressive strength attained. A model of the influence of nickel sand consolidations on well productivity is presented to show that very little productivity is presented to show that very little impairment is to be expected.

Introduction
Electroless nickel plating for sand consolidation was perfected in the latter half of the 1960's. A general description of the plating process and deposit properties is available in Ref. 1. Design procedures properties is available in Ref. 1. Design procedures for consolidation, along with a description of system chemistry, is provided in Ref. 2, a companion to this paper. The process involves injecting a catalyst that paper. The process involves injecting a catalyst that activates the sand and then injecting various aqueous solutions of nickel salts containing a chemical reducing agent. The metal layer deposits spontaneously on the sand grains, binding them into a consolidated mass. Although originally developed for higher-temperature applications up to about 550 degrees, far beyond the useful range of plastic sand-consolidation treatments, electroless nickel sand consolidations are available for the full range of reservoir temperatures. Nickel-consolidated sands exhibit compressive strengths much higher than organic cementing materials, with the strength highest near the wellbore, and require no curing time. Furthermore, since consolidation permeabilities depend strongly on nickel content, the placement tends to be self-regulating. Zones of initially higher permeability tend to be brought to the same level as permeability tend to be brought to the same level as the bulk of the formation to be treated; consequently, placement becomes more uniform. placement becomes more uniform.Electroless nickel plating has successfully consolidated a wide variety of materials, ranging from 700-micron ground walnut shells, to glass beads of all sizes, through fine, high-clay-content sands, as well as the typical Gulf Coast formation sands. Job design primarily depends on the specific surface area of the material to be plated and on the plating temperature. A variety of chemical systems plating temperature. A variety of chemical systems are available, depending on the application in question. Yet, even with significant uncertainty in the design parameters, successful consolidations can be expected. parameters, successful consolidations can be expected.Presented here are the results of core flow consolidations illustrating how the nickel content, porosity, permeability, and compressive strength is porosity, permeability, and compressive strength is likely to vary according to plating conditions. A model of the plating process that assumes uniform coatings around the sand grains leads to a simple permeability-porosity relationship that is in good permeability-porosity relationship that is in good agreement with experimental measurements, at least for porosity reductions of less than 50 percent. The influence of the consolidation on well productivity is examined, assuming a linear porosity profile, to show only minor "impairment."

EXPERIMENTAL PROCEDURES AND RESULTS
The standard test material was Clemtex No. 5 sand, a clean, rounded, 80-120 mesh sand often used in formation simulation. Although results presented here are only for this material, other materials already cited exhibit the same general behavior. Design conditions were chosen to achieve 100-cc consolidations. The design specification involves choosing flow rate and solution composition for a given sand specific surface area and plating temperature. Design details are available in Ref 2. The sand was packed into steel pipe sections, with appropriate packed into steel pipe sections, with appropriate retaining screens, flow distributors and compression springs at each end. The packed pipe sections were then connected to the flow system, preceded by a constant-rate Whitey pump and followed by a backpressure regulator and gas-liquid separator. The pipe section was set into a constant temperature bath, and injected solutions were heated to the desired bath temperature before reaching the sand. The volume of plating solution was about 75 PV.
SPEJ
P. 203