Study On The Water Soluble Styrene Sulfonic Acid Sodium-acrylic Acid-acrylic Amide Copolymer Fluid-loss Agent By Microemulsion Polymerization

In the petroleum well drilling process, the control of drilling fluid's filter loss has the vital significance to protect the mud shale, wall as well as the production protection. The use of drilling fluid fluid-loss agent is the most effective method. Up to now although many kinds of drilling fluid fluid-loss agent can be selected to decrease the drilling fluid's filter loss, the performance is not ideal, especially in the process of deep well cementation with high temperature and high salt solution.This article attempts to use Span80 and Tween80 as the mixed surfactants, acrylic acid(AA), acrylic amide(AM) and styrene sulfonic acid sodium(SSS) as comonomers, cyclohexane as the oil phase, ammonium persulfate and sodium bisulfite as the redox initiator to synthesize water soluble copolymers of AM-AA-SSS as drilling fluids by inverse microemulsion polymerization. The paper has studied systematically the effects of redox initiator amount, polymerization temperature, Tween 80/Span 80 mass ratio, styrene sulfonic acid sodium(SSS) amount, etc on the intrinsic viscosity and monomer conversion, and has also evaluated these effects on the drilling fluid general performance . The structure and the thermo stability of the synthesized water soluble copolymer were characterized by infrared spectrum (FTIR) and the thermal analysis (TGA). SEM was used to analyze the filter cake mophologies of the polymer drilling fluids. We have obtained termerature-resistant and salt-resistant polymer drilling fluids with good overall performances. The main results are as follows:(1) To realize the objectives of a stable and rapid polymerization and copolymers with high molecular weight, the polymerization technique has been optimized and the optimal polymerization parameters are as follows: AA/AM mass ratio of 3:7; SSS amount of 15%;initiator amount of 1%; Tween 80/Span 80 mass ratio of 1:3; polymerization temperature of 60℃.(2) The synthesized AA/AM/SSS copolymers showed higher resistance to Ca2+ than to Na+, an indicative of good salt-resistance of the synthesized AA/AM/SSS copolymers.(3) The filter loss of the polymer drilling fluids decreases and the filter cake become compact and thin with increase of SSS amount in copolymer in a certain range. The optimal SSS amount used in copolymer is 15%.(4) The filter loss of the polymer drilling fluids increase slightly with increase of salt concentration and temperature, an indicative of good termerature-resistance and salt-resistance of the polymer drilling fluids.(5) FTIR spectra showed the characteristic absorption peaks related to amide group, sulfonic group and carboxyl group, an indicative of the structure of AA/AM/SSS copolymers.(6) The onset decomposition temperature of the copolymer increases from 215℃to 225℃and the residue also increases at 500℃with SSS amount in copolymer increasing from 10% to15%.