Oilfield Scale Inhibitors Research Articles

Synthesis and Characterization of Modified Aliphatic Polycarbonates as Environmentally Friendly Oilfield Scale Inhibitors

Oilfield scale inhibitors have been used for many decades, mostly to fight carbonate and sulfate scaling. Many inhibitors are known, but only a few show good biodegradation to make them environmentally acceptable in areas with strict regulations, such as offshore Norway. Often high biodegradation is at the expense of other useful properties, such as thermal stability for high-temperature squeeze applications. We have now synthesized and investigated a new class of polycarbonate polymers with pendant anionic functional groups (carboxylate and phosphonate) as potential oilfield scale inhibitors. These polymers have a carbonate group in the backbone. Polymers with carboxylate and phosphonate side groups were prepared. We report here the scale inhibition performance of these polymers at 100 °C against both calcite and barite scaling at typical North Sea conditions in dynamic tube-blocking equipment, both before and after aging at 130 °C. The phosphonated copolymer gave very good performance against calcite sc...

Synthesis and Evaluation of New Bisphosphonates as Inhibitors for Oilfield Carbonate and Sulfate Scale Control

Most non-polymeric oilfield scale inhibitors contain aminomethylenephosphonate groups. They generally have poor biodegradability, limiting their use in regions with strict environmental regions, such as offshore Norway. From mono- and bisnitrile starting materials, we have synthesized and investigated compounds with one or two aminobisphosphonate groups, −C(NH2)(PO3H2)2, for seawater biodegradability, their calcium carbonate and barium sulfate scale inhibition, and compatibility with Ca2+ ions. The distance between these groups was shown to affect biodegradability, with aminobisphosphonate derived from adiponitrile, (1,6-diaminohexane-1,1,6,6-tetrayl)tetraphosphonic acid (BP-7), giving the highest biodegradation of 25% in 28 days by the OECD 306 seawater test. All of the synthesized inhibitors exhibited both carbonate and sulfate scale inhibition properties. In comparison to known commercial scale inhibitors, the scale inhibition performance was relatively poor for sulfate scale and moderate for carbonate...

Automatic optimization of oilfield scale inhibitor squeeze treatment designs

Squeeze treatments are one of the most common methods to prevent oilfield scale deposition, which in turn is one of the most significant flow assurance challenges in the oil industry. Squeeze treatments consist of the batch injection of a chemical scale inhibitor (SI), which above a certain concentration, commonly known as MIC (Minimum Inhibitor Concentration), prevents scale deposition. The most important factor in a squeeze treatment design is the squeeze lifetime, which is determined by the volume of water or days of production where the chemical return concentration is above MIC, which commonly is between 1 and 20ppm. Typically, squeeze treatment designs include the following four stages: a preflush, acting as a buffer; the main slug, where the main chemical slug is injected; the overflush, which will displaced the chemical pill deeper into the formation and finally, a shut-in stage, which allows the chemical to be further retained in the formation.The main purpose of this paper is to describe the automatic optimization of squeeze treatment designs using an optimization algorithm, in particular, using particle swarm optimization (PSO). The algorithm provides the optimum design for a given set of criteria that are used in a purpose built reactive transport model of the near-wellbore area. Every squeeze design is fully determined by a number of parameters; namely, injected inhibitor concentration, main slug volume, overflush volume and shut-in time. The parameter space is bound to certain limits, which will be determined by the maximum injected concentration, main slug and overflush volumes. The maximum injected concentration might be determined by, amongst other issues, logistics, economics and/or compatibility with other chemicals. The main slug and overflush maximum volumes may be identified by the well engineer based on concerns of water formation damage, hydrate formation and/or gas lifting limitations, which might be lower for high value wells. This approach still requires engineering input and review, but speeds up the process of finding an optimum design, and reduces risk of non-optimal squeeze treatments being performed.

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

Systematic evaluation of the transport and return behavior of a Ca–DTPMP reverse micelle nanomaterial and nanofluid for oilfield mineral scale control.

Automatic Isotherm Derivation From Field Data for Oilfield Scale-Inhibitor Squeeze Treatments

SummaryOilfield scale formation represents a significant flow-assurance challenge to the oil and gas industry, because of increasing water production worldwide and higher oil prices. Scale-inhibitor (SI) squeeze treatment is the most widespread method to combat downhole scaling. To predict SI squeeze treatments accurately for further optimization, it is necessary to simulate the SI retention in the formation, which may be described by a pseudoadsorption isotherm. Although these are often derived from coreflood experiments, sometimes they are not appropriate for modeling well treatments because the core tests on which they are based cannot fully represent field-scale processes. In practice, the parameters of an analytic form of the isotherm equation are modified by trial and error by an experienced practitioner until a match is obtained between the prediction and the return profile of the first treatment in the field.The main purpose of this paper is to present a stochastic hill-climbing algorithm for automatic isotherm derivation. The performance of the algorithm was evaluated by use of data from three field cases. Two success criteria were defined: the ability to match a single historical treatment and the ability to predict subsequent successive treatments. To test for the second criterion, a candidate isotherm was derived from the first treatment in a well that was treated with the same chemical package on consecutive occasions, and then the predictions by use of the suggested solution were compared with the observed SI concentration-return profiles from the subsequent treatments. In all the calculations, the performances of both the isotherms suggested by the hill-climbing algorithm and the isotherms derived by trial and error were compared. The results demonstrate that the hill-climbing algorithm is an effective technique for deriving an isotherm for a single treatment, although predictions for successive treatments worsened slightly with each treatment.

Effect of Various Cations on the Formation of Calcium Carbonate and Barium Sulfate Scale with and without Scale Inhibitors

High pressure dynamic tube blocking tests have been conducted to determine the effect of iron (divalent and trivalent), calcium, magnesium, and sodium ions on the formation of calcium carbonate and barium sulfate scale with and without added scale inhibitors. Scale inhibitors were chosen to represent the three main functional groups used in commercial oilfield scale inhibitors: the phosphonate group (found in sodium diethylenetriaminepentaphosphonate), the carboxylate group (in sodium polyaspartate), and the sulfonate group (in sodium polyvinysulfonate). A fourth proprietary inhibitor with phosphonate and carboxylate groups was also used in some studies.

The Influence of Formation Calcium and Magnesium on the Effectiveness of Generically Different Barium Sulphate Oilfield Scale Inhibitors

Summary Using chemical scale inhibitors is one of the most common methods of preventing downhole and topside mineral scale formation in oil fields. Several aspects of the brine composition may affect the performance of the various scale inhibitors. In this paper, we focus on the roles of calcium and magnesium ion concentrations. The calcium concentration in a particular reservoir and in the inhibitor slug often determines the extent to which the inhibitor species is retained in the near-wellbore area (i.e., on its adsorption or precipitation behavior). What is less well understood is the effect of divalent cations on the inhibition process itself. Common ion effects are well known; however, for pentaphosphonate inhibitor species (e.g., DETPMP), significant improvements in inhibition efficiency have been reported by increasing the calcium concentration in the solution. In this paper, we expand significantly on such observations. The effect of calcium and magnesium cation concentrations is examined for a wide range of generically different inhibitor species, including pentaphosphonate, hexaphosphonate, phosphinopolycarboxylate, polyvinyl sulphonate, and sulphonated polyacrylate copolymers. The results clearly indicate how different inhibitor species are affected quite differently by changes in [Ca2+] and [Mg2+] and how this difference relates to the cation affinity of the inhibitors active functional groups. The results were obtained by comparing the barium sulphate inhibition efficiency of various species in mixtures of a low/medium scaling (Brent type) formation brine and seawater (SW) and also in a more severe scaling (Forties type) formation brine/SW mixture. Barium sulphate inhibition efficiencies were examined by static inhibition efficiency tests, with residence times ranging from 30 minutes to 24 hours. Phosphonates are shown to be poor inhibitors at very low [Ca2+], indicating that their effectiveness is controlled by the formation of Ca2+/phosphonate inhibitor complexes, as discussed in previous works.1,2 On the other hand, polymeric polycarboxylate inhibitors are shown to be effective even at very low [Ca2+], indicating that the formation of multiple bonds between the polymer and the crystal surface allows for stronger adsorption and, thereby, inhibition. However, it appears that strong ionic bonds involving calcium cation bridging are required for the phosphonate-based species. Conversely, when the magnesium ion concentration is increased, the performance of the phosphonate is significantly reduced, whereas the other polymeric species are relatively unaffected. This can be accounted for in terms of the cation affinity of different inhibitor functional groups in a similar manner as comparative adsorption and inhibitor/brine compatibility effects. For the polycarboxylate inhibitor species examined in this work, a clear maximum in inhibition efficiency is observed with increasing calcium concentration. This is explained, from related experiments, in terms of complexation (incompatibility) and differences in the adsorption modes at the scale surface.