Lewis R. Norman

Effects of Oxygen on Fracturing Fluids

The stability of polysaccharide gels at high temperature is limited by such factors as pH, mechanical degradation, and oxidants. Oxygen is unavoidably placed in fracturing fluids through dissolution of air. To prevent premature degradation of the fracturing fluid by this oxidant, oxygen scavengers are commonly used. In this paper, the effects of oxygen and various oxygen scavengers on gel stability will be presented. Mechanical removal of oxygen resulted in surprisingly stable fracturing gels at 275 F. However, chemical removal of oxygen gave mixed results. Test data from sodium thiosulfate, sodium sulfite, and sodium erythorbate used as oxygen scavengers/gel stabilizers showed that the efficiency of oxygen removal from gels did not directly coincide with the viscosity retention of the gel, and large excesses of additives were necessary to provide optimum gel stabilization. The inability of some oxygen scavengers to stabilize the gel was the result of products created from the interaction of oxygen with the oxygen scavenger, which in turn, produced species that degraded the gel. The ideal oxygen scavenger should provide superior gel stabilization without creating detrimental side reaction products. Of the materials tested, sodium thiosulfate appeared to be the most beneficial.

Application of curable resin-coated proppants

Laboratory investigation of the interactions between fracturing fluids and resin-coated proppants (RCPs) revealed (among other conclusions) that RCPs are incompatible with oxidizing breakers. Areas covered included RCP effect on fluid rheology, fluid relationship to RCP strength, theoretical study of required RCP strengths to prevent flowback, and experimental measurement to establish minimum strength

Temperature-stable acid-gelling polymers: laboratory evaluation and field results

A systematic evaluation of the hydrolytic stability of various types of polymers was made and rheology data were obtained for various types of polymers to evaluate their temperature thinning properties. The ability of several systems to produce viscosity (as a function of molecular weight), was studied and finally, a polymer gelling agent was selected which is useful for oil well acidizing operations up to 400/degree/F. 12 refs.

Research in particle coating and agglomeration at West Virginia University

Abstract Over the last three years, work in the Particle Coating Laboratory at West Virginia University has focused on three main areas. The first area concerns the reversible agglomeration of cement to produce a granular product (2–10 mm) that can be transported easily and can be broken down and hydrated to form a cement slurry with properties identical to virgin cement. This agglomeration process uses a binding agent consisting of calcium chloride (CC) and tartaric acid (TA) dissolved in methanol that can be considered an inert solvent. By adjusting the proportions of the cement set accelerating agent (CC) and the retarding agent (TA) a granular cement product can be formed that gives a cement slurry with essentially the same characteristics as that obtained from virgin cement. The resulting concrete also has the same compressive strength, obtained in a standard 3-day test, as virgin cement. The second research area concerns the formation of encapsulated brittle particles of ammonium persulfate (AP) that are used as viscosity breaking agents for fracturing fluids. In order to obtain a coat that under goes brittle fracture when subjected to a compressive load, a coating of a cross-linked acrylate polymer containing up to 80 wt.% of fine ( The third project consists of the video imaging of particle movement in a semicircular fluidized bed typically used in coating operations. The particles of interest are 8-mm-diameter tablets. The technique used to capture particle velocity data utilizes two CCD cameras that are synchronized to capture images that are between 1 and 5 ms apart. The mapping of particle velocity within the spray region in the draft tube insert under a variety of conditions is currently underway. Preliminary data is presented and discussed.

Study of Continuously Mixed Crosslinked Fracturing Fluids With a Recirculating Flow-Loop Viscometer

Continuously mixed gel fracturing fluids were successfully prepared with polymer slurries of guar, derivatized guar, and derivatized cellulose. The authors describe the rheological behavior of the continuously mixed fluids measured on a recirculating flow-loop viscometer over a temperature range of 80 to 300{sup 0}F (27 to 149{sup 0}C). Rapid and complete base-gel hydration required proper pH control and high mixing energy. Oil-based polymer slurries allowed rapid hydration rates sufficient to achieve performance from a crosslinked fluid prepared during a completely continuous operation. Water-based polymer slurries required a short holding period for complete hydration. Delayed-crosslink-gel viscosity was influenced by shear rate and the degree of base-gel hydration. Chemical factors influencing viscosity development included base-gel concentration, crosslinking-agent concentration, fluid pH, and ionic strength. Hydration time and pH requirements may differ for specific polymer/crosslinker pairs.

New Breaker Technology for Fracturing High-Permeability Formations

Regained permeability studies with HEC polymer in high-permeability cores revealed that persulfate-type oxidizing breaker and enzyme breaker do not adequately degrade the polymer. Use of high concentrations of acid or peroxide breakers did show improved breaking, but additional work is needed to apply high concentrations of these breakers properly. Sodium persulfate breaker was found to be thermally decomposed, and its decomposition was accelerated by formation minerals. Enzyme breaker adsorbed onto the formation, but still partly functioned as a breaker. Dynamic fluid-loss tests with reduced-pH, borate-crosslinked gels suggest that accelerated leakoff away from the wellbore could be obtained through the use of a delayed-release acid. Rheological measurements confirmed that a soluble delayed-release acid could be used to convert a borate-crosslinked fluid into a linear gel. This conversion was visually confirmed by /tests involving a delayed-release acid and a borate-crosslinked fluid in a single-pass flow loop apparatus. Higher concentrations of breaker were placed in a borate-crosslinked fluid by encapsulating the breaker, and controlled viscosity reduction was obtained. A simulation using a 3D commercial simulator showed improved cumulative oil production when increased fluid loss from a soluble delayed-release acid was applied.

Using the hollow-core test to determine acid reaction rates

Effects of chemical additives on acid reaction rates may be determined by observation of acid reaction in hollow limestone cores. Reactivities of acids containing (1) surfactant gelling agents, (2) polymeric gelling agents, (3) crosslinked polymeric gelling agents, and (4) fluid loss additives were measured. Effects of chemical and filter cake retardation were assessed, and experiments were conducted with and without fluid leakoff at temperatures of 150 to 300/sup 0/F (65 to 150/sup 0/).