The Effects of Barium Sulfate Saturation Ratio, Calcium, and Magnesium on the Inhibition Efficiency—Part I: Phosphonate Scale Inhibitors

Abstract

Conventional phosphonate-type scale inhibitors (SIs) are commonly applied for barite-scale prevention in oil fields. The barite forms when the injection water (IW), which is usually sulfate rich, is injected into a barium-containing formation water (FW). The inhibition efficiency (IE) of barite-scale inhibitors is affected by the barium sulfate saturation ratio (SR) of the brine mix and, additionally, by the presence of divalent cations Ca 2þ and Mg 2þ . What is less well known is that the precise balance between these factors (SR and Ca 2þ /Mg 2þ ratio) can vary significantly for different phosphonate species. This paper presents novel IE experimental results for phosphonate-scale inhibitors DETPMP and HMTPMP (penta-phosphonates), OMTHP (hexa-phosphonate), and HMDP (tetra-phosphonate). Minimum-inhibitor-concentration (MIC) levels for each SI are established by testing a wide range of brine IW/FW mixing ratios, which changes (i) barite SR and precipitated mass, (ii) molar ratio of Ca 2þ /Mg 2þ , and (iii) the ionic strength of the brine mix.The phosphonate SIs were categorized into two types on the basis of their MIC-vs.-percent-North Sea-seawater (NSSW) behavior. Type 1 (e.g. DETPMP and OMTHP) are affected principally by SR and are rather less sensitive to Ca 2þ /Mg 2þ ratio although they do show some sensitivity to the latter factor. Type 2 (e.g., HMTPMP and HMDP) are severely affected by brine Ca 2þ /Mg 2þ ratio as well as SR. To demonstrate these effects conclusively, a series of IE experiments is presented with varying [Ca 2þ ] and [Mg 2þ ] (which normally occurs in the field as the IW/FW ratio changes over time) and then similar experiments are repeated at a fixed Ca 2þ /Mg 2þ molar ratio. The MIC level measured for both types of phosphonate SI always correlates very well with the barite SR at fixed Ca 2þ / Mg 2þ molar ratio (fixed case). In addition, we find the MICs of both types of SI are much lower in the fixed-case experiments (higher Ca 2þ /Mg 2þ molar ratio), compared with the base case, because of the beneficial effect of higher [Ca 2þ ]. The effects observed are important for field application of phosphonate SIs because they show how the various species are sensitive to the changing scaling problems as the %NSSW increases, in terms of SR and Ca 2þ /Mg 2þ molar ratio. These results also give some important insights into the mechanism by which different phosphonates actually work in inhibiting barite scale.

Scale-Inhibitor Consumption in Long-Term Static Barium Sulfate Inhibition Efficiency Tests

“…This SI consumption pattern correlates very well with the DETPMP IE (Fig. 2) and the known effects of Ca 2þ /Mg 2þ on phosphonate SIs(Shaw et al 2012a) (i.e., Ca 2þ beneficial, Mg 2þ detrimental) because more active SI remains in solution when the Ca 2þ /Mg 2þ molar ratio is higher.SI Consumption Experiments TestingPhosphonates. The second experiment involved testing a range of five phosphonate SIs: OMTHP, DETPMP, HMTPMP, HMDP, and NTP in a 50:50 basecase brine mix.…”

“…Perhaps the higher [Ca 2þ ] in the Ca 2þ / Mg 2þ ¼ 1.64 case is enabling a larger percent of SI to be consumed into the forming scale. As already established by Shaw et al (2012a), phosphonate SIs perform better in high [Ca 2þ ] mixes. However, note that HMTPMP was tested at 6 ppm with Ca 2þ /Mg 2þ ¼ 1.64 and at 20 ppm with Ca 2þ /Mg 2þ ¼ 0.19 (i.e., HMTPMP was not tested at the same [SI] in both tests).…”

“…Differences in SI consumption will also have a direct effect upon its adsorption and retention characteristics; these properties are also very important with respect to oilfield applications and are also affected by pH, [Ca 2þ ], [Mg 2þ ], and other factors (Davis et al 2003;Sorbie et al 1993). The factor that led us to examine SI consumption was that the Type 1 species appear to show similar IE at 2 and 22 hours, whereas the IE of Type 2 species usually declines markedly over time (Shaw 2012;Shaw et al 2012aShaw et al , 2012b. Many SI consumption-type experiments have been performed (>100), and a pattern has emerged.…”

Creation and study of formulations as inhibitors of metal corrosion and scaling for stabilization water treatment in water utilization systems (a review)

“…EDTP, DTPP, TTHP have been studied as inhibitors of barium sulfate (barytes) sedimentation from brine in oil-field equipment. Barite is formed upon mixing injected water, which is usually rich in sulfates, into well water containing Ba(II) [20]. The minimum working concentration has been determined for each type of inhibitor depending on the ratio of injected water and water containing Ba(II), which results in a change BaSO 4 saturation coefficient and in precipitation, the Ca 2+ /Mg 2+ molar ratio, and brine ionic strength.…”

Influence of Terpolymer Based on Amide, Carboxylic, and Sulfonic Groups on the Barium Sulfate Inhibition

“…However, the maximum thermodynamic scaling tendency (SR), which is essentially the driving force to reach equilibrium precipitation, is at 60/40 SW/FW mix. Therefore, in order to inhibit the formation of barium sulfate, a lower concentration of scale inhibitor will be required for the 10/90 SW/FW mix, since this system has a lower scaling tendency; whereas a much higher quantity of SI would be required to inhibit the 60/40 SW/FW mix, since this case has the highest scaling tendency for this system. − …”