Effect of carboxylic group on the compatibility with retarder and the retarding side effect of the fluid loss control additive used in oil well cement

Effect of a 2-Acrylamido-2-methylpropanesulfonic Acid-Based Fluid Loss Additive on the Hydration of Oil Well Cement

The fluid loss additive is to prevent the cement slurry from filtrating water to the formation under pressure. 2-Acrylamido-2-methylpropanesulfonic acid (AMPS)-based fluid loss additive mainly works by adsorbing on the surface of cement particles. The adsorption affects cement hydration. In this paper, the effect of one kind of AMPS-based fluid loss additive (A-FLA) on the hydration of oil well cement was studied. The water loss, setting time, thickening time, and compressive strength of cement slurry with various amounts of FLA were measured. In addition, the hydration heat of the cement slurry, FLA adsorption isotherm on cement particles, and hydration minerals were studied. The results showed that A-FLA had a good water loss control ability. The water loss of the cement slurry decreased slowly with the increase of A-FLA dosage when the adsorption capacity exceeded 4.47 mg/g. The low adsorption capacity of A-FLA (less than 4.47 mg/g) had a significant impact on the thickening time. With an adsorption capacity greater than 4.47 mg/g, the thickening time varied minimally. A-FLA mainly delayed the hydration of C3S at 1 day and reduced the production amorphous phase.

Synthesis and Evaluation of Highly Inhibitory Oil Well Cement Retarders with Branched-Chain Structures

Cementing at medium temperature and high temperature (90-150 °C) is facing challenges on account of the properties of the retarders. Except for the thermal stability, abnormal gelation, such as "bulging" and "stepping", often takes place and results in safety problems. In this article, the synthesis of a new retarder DRH-150 was introduced. First, a main chain with thermal-resistant groups, 2-acrylamido-2-methylpropanesulfonic acid-acrylic acid (AMPS-IA-AA) was prepared by free radical polymerization. Second, the retarder with a branched structure was synthesized by the grafting reaction. Evaluation of the construction performance showed that, within the temperature range from 90 to 150 °C, the initial viscosity of the cement slurry with DRH-150 was less than 15 Bc, exhibiting an adjustable thickening time and a dosage sensitivity of less than 20%. Meanwhile, no abnormal gelation phenomenon was observed. Referring to the static gelation, both the transition time and the starting strength time (1 MPa) were short. The overall results proved that the retarder DRH-150 might ensure the safety of well cementing and improve the wellbore sealing effect in deep wells, ultradeep wells, and complex wells.

Function Synergy of Cross-Linked Cationic PVA Polymer to AMPS-Type Fluid Loss Additive Used for Cement-Based Material

In this research, a kind of 2-acrylamido-2-methylpropanesulfonic acid sodium salt- (AMPS-Na-) type copolymer additive, the fluid loss additive (FLA), named as FLA A additive, was used for research. The performance of FLA A was tested and found to fail in the effective control of free water and to hinder the hydration process for delaying the breaking of the early hydration shell. The reason for it was the absorbed behavior and chelating effect of the AMPS-Na unit to Ca2+ hydrating cement particles. Thus, a cationic polyvinyl alcohol (PVA) polymer, modified by glyoxal and boric acid, was discovered due to its excellence in associating with the FLA A additive for controlling the free cement-based material water amount and preventing the chelating effect of FLA A chains on the surface of the cement-based material. Glyoxal/boric acid-modified polyvinyl alcohol, abbreviated as PVAGB or PVA-G-B, was with special molecular properties, i.e., positive ZETA (ζ) potential characteristics and cross-linked molecular structure. Due to competitive absorbed behavior of glyoxal-modified hydroxyl groups and free Ca2+ released by the hydration product, the chelating effect of AMPS-Na units to Ca2+ was weakened and the possibility of FLA A chains being absorbed to the surface of the cement-based material was decreased. Then, the formation of a complete fluid loss system was obtained; i.e., the fluid loss volume decreased to less than 50 mL at 30°C and 108 mL at 80°C with 0.2 percentage by weight of cement (%BWOC) of PVAGB and 0.50%BWOC (percentage by weight of cement) of FLA A. Besides, the hydration process of cement-based material was accelerated due to formation of more C-S-H gels in the early hydration period. As a result, the cement-based material not only showed no worse compressive-strength retrogression but also showed a stable 28-day compressive strength of 28 MPa.