Mechanistic Understanding of Rock/Phosphonate Interactions and the Effect of Metal Ions on Inhibitor Retention

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper discusses the effects of Ca 2+ , Mg 2+ , and Fe 2+ on inhibitor retention and release. Better understanding of phosphonate reactions during inhibitor squeeze treatments has direct implication on how to design and improve scale inhibitor squeeze treatments for optimum scale control. Putting various amounts of metal ions in the inhibitor pill adds another degree of freedom in squeeze design, especially in controlling return concentrations and squeeze life.Phosphonate reactions during squeeze treatments involve a series of self-regulating reactions with calcite and other minerals. However, excess calcite does not improve the retention of phosphonate due to the surface poisoning effect of Ca 2+ . The squeeze can be designed so that maximum squeeze life is achieved by forming a low solubility phase in the formation. Addition of Ca 2+ , Mg 2+ , and Fe 2+ in the pill solution at 0.1 to 1 molar ratios significantly improves the retention of phosphonate. Alternatively, these metal ions can be dissolved from the formation while an acidic inhibitor pill is in contact with the formation minerals. Both BHPMP and DTPMP returns were significantly extended by the addition of metal ions, e.g. Ca 2+ and Fe 2+ . The addition of Mg 2+ may increase the long-term return concentration, which is important for some wells where a higher inhibitor return concentration is needed.The laboratory squeeze simulations were compared to two field return data obtained from squeeze treatments performed on two wells located in a sandstone reservoir in Saudi Arabia. The sandstone formation contains significant amounts of ironbearing minerals.

Synthesis and laboratory testing of a novel calcium-phosphonate reverse micelle nanofluid for oilfield mineral scale control

“…Calcite was chosen as the representative formation medium material in that calcite is the most active ingredient among various types of formation minerals to react with phosphonate inhibitors. 36,37 Similar to our previous studies, the transport of RM nanomaterials can be delineated by advection and diffusion mechanism as well as particle ltration and attachment mechanism. 15,17 Of particular interest in this study is the impact of preush uid on RM nanomaterial transport.…”

Transport and return of an oilfield scale inhibitor reverse micelle nanofluid: impact of preflush and overflush

“…Similar to the eld squeeze job, squeeze simulation test comprises of consecutive steps of preush, inhibitor injection, overush, shut-in and inhibitor return. 7,9 Typically, oileld squeeze treatment employs an aqueous inhibitor solution as the pill solution. In the past few years, the idea of utilizing inhibitor-containing nanomaterial uid (nanouid) as an inhibitor delivery vehicle has been reported and tested via a number of laboratory column transport and squeeze simulation tests.…”

Enhanced transport of novel crystalline calcium-phosphonate scale inhibitor nanomaterials and their long term flow back performance in laboratory squeeze simulation tests

“…During production following the squeeze treatment, the injected inhibitors will be gradually desorbed into the formation brine and ow back at certain concentrations. In many laboratory investigations and eld observations, 3,[7][8][9][10] the inhibitor ow back concentration quickly reaches a peak value and declines to a low plateau level for a period of time. An adsorption squeeze is oen carried out by injecting a neutralized pill into formation.…”

“…The principle scale deposition mechanisms in offshore productions include: (1) the change in pressure and temperature; (2) the mixing of incompatible uids and (3) the increase of salt concentration. [1][2][3][4] Phosphonates are widely used scale inhibitors in the oileld to prevent scale formation. Conventionally, phosphonate inhibitors are applied in production wells via a squeeze treatment.…”

“…However, it is observed that 7 the acidic pills are mostly precipitated near the wellbore, leading to a limited protection area; the neutralized pills are able to migrate deeper into the formation, but only a small portion of the inhibitors can be retained by the formation medium, a large fraction of the inhibitors being eluted out of the reservoir during the initial return. 3,4 Some recent advances in oileld scale control technologies include the utilization of viscosied uids and non-aqueous inhibitor solutions. 11 Vis-cosied uids were investigated to place scale inhibitors into formation via bullheaded application.…”