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The recent advances in drilling and completion technology have led to the development of more complex reservoirs including high pressure, high temperature, and high salinity (HP/HT/HS) fields. A combination of high calcium and barium concentrations in the produced water, coupled to high reservoir temperatures presents a particularly harsh scaling environment which dictates the need for high concentrations of exotic scale inhibitor chemistry for effective downhole scale control. These high levels of inhibitor, typically 10-200 ppm, are particularly difficult to sustain over long production periods leading to a relatively short squeeze life and thus, high well intervention frequency and deferred oil costs. In addition, increasing environmental regulations have made the development of green chemistry a high priority.
A number of scale inhibitor chemistries have been shown to be thermally stable and effective at controlling scale deposition under harsh conditions, however, their retention characteristics are less than ideal, leading to short treatment life. In addition, some of these chemistries do not have favourable environmental properties.
To meet the challenges presented by the more severe water chemistries and producing environments a new chemistry was developed. The new chemistry contained vinyl sulphonate monomer species, which were expected to provide the polymer with a high level of thermal stability, calcium tolerance and effective barium inhibition properties. The incorporation of a phosphorus containing monomer was expected to provide good retention properties and relative ease of detection. In addition, the use of the novel phosphorus containing monomer offered the opportunity to increase the biodegradation characteristics of the developed polymer.
Laboratory studies have suggested that the new inhibitor combines significantly improved thermal stability, calcium tolerance, and barium inhibition with superior retention and environmental properties. Nine squeezes with the new inhibitor have been completed in the North Sea, which have already achieved a significant increase in squeeze life1.
The challenge presented by the scale mangement of HP/HT/HS fields has been to identify a scale inhibitor chemistry that has the desirable characteristics of good retention and release, ease of detection, calcium tolerance, thermal stability and was ecofriendly. Previously, vinyl sulphonate copolymers and phosphonate based scale inhibitors have been deployed to control scale under harsh conditions. However, while the vinyl sulphonate copolymers are effective at the prevention of barium based scales they have the disadvantages of poor retention and difficulty of detection. In contrast, while phosphonate based inhibitors are effectively retained within the reservoir they suffer from a combination of poor calcium tolerance, thermal stability and environmental properties. Recognising the advantages of the two inhibitor chemistries, the challenge was to combine the benefits of the vinyl sulphonate and phosphonate functionalites to form a green chemical capable of operating effectively within a harsh environment.
To meet this challenge, copolymers were prepared containing varying amounts of vinyl sulphonate and different phosphorus tagged monomers. The rationale behind the incorporation of phosphorus tagged monomers was the potential for enhanced retention of the inhibitor and for ease of residual inhibitor detection. One of the polymers developed, consisted of a novel phosphorus containing monomer, which had been custom synthesised in the laboratory and was not available commercially. The polymer developed with this novel monomer was shown to have very desirable properties including calcium tolerance, barium sulphate inhibition and excellent retention and environmental properties.
Abstract Desired production chemicals such as scale inhibitors, paraffin inhibitors and corrosion inhibitors can be adsorbed onto a proppant-sized solid particle for controlled release. This solid additive was first introduced for field application through a fracture stimulation operation in 2004. More than 25,000 (mostly in North America) wells have been treated with this solid inhibitor since then. In this strategy, the solid inhibitor additive is pumped with the proppant and distributed evenly throughout the created fracture. A prolonged protection for flow assurance problems can be achieved as the inhibitor slowly desorbs into the produced fluids. A conventional phosphonate-based liquid scale inhibitor treatment has been proven to be ineffective when deployed in North Dakota to prevent the formation of mineral scale in the downhole pump and production tubing. In 2010, a novel biodegradable scale inhibitor-based solid additive was developed, deployed successfully, and the application for one operator in this area was presented (Szymczak, et al., 2010). The present paper updates those results and discusses results from 14 additional operators with more than 500 treated wells. The discussion in this paper is mainly focused on the correlation between solid inhibitor loading, water/oil production and projected protection longevity based on the scale inhibitor residuals data monitored for more than 100 wells. The economic and environmental benefits of this new environmentally preferred product, and related lessons learned are also included.
Chen, Ping (Halliburton, Multi-Chem) | Rawlins, Scott (Halliburton, Multi-Chem) | Hagen, Thomas (Halliburton, Multi-Chem) | Huijgen, Martijn (Halliburton, Multi-Chem) | Yue, David Zhiwei (Halliburton, Multi-Chem) | Hamam, Mohammed (Halliburton, Multi-Chem) | El Hajj, Hicham (Halliburton, Multi-Chem) | Al-Ghamdi, Tawfik (Halliburton, Multi-Chem)
Abstract A strategy combining fracturing and downhole scale inhibitor squeeze treatments was employed in an extremely tight high-temperature gas reservoir (200°C) with calcite and sulfate scaling problems. Challenges included developing a scale inhibitor that is thermally stable at this high temperature, fully compatible with the fracture fluid used, extremely beneficial with a low minimum effective concentration, with good adsorption/desorption properties for a long squeeze treatment life. Literature survey verifies that few reports are published discussing application of a combined fracture and downhole scale inhibitor squeeze treatment under such high-temperature reservoir conditions. Multiple laboratory tests were performed to qualify the scale inhibitor, including inhibitor dynamic tube blocking, static beaker, and fracture fluid property testing. Standard inhibition tests were adapted to confirm tests were designed to confirm that the scale inhibitor was thermally stable under application conditions (i.e., the scale inhibitor was blended with the fracture fluid (including breaker) at given concentrations and aged together at 200°C for a certain period). The aged scale inhibitor sample was then tested for its performance against scale and results compared to the unaged inhibitor sample. Further tests were designed for fracture fluid rheology and breaking time with the blended scale inhibitor to help ensure the scale inhibitor was fully compatible with the fracturing fluid and would not interfere with its properties. Laboratory test results demonstrated that the scale inhibitor is fully compatible with the fracturing fluid and formation brine. An extremely low minimum effective concentration of the scale inhibitor was determined to be 5 ppm with the aged and unaged scale inhibitor samples. With the addition of the scale inhibitor, the breaking time and rheology property of the fracture gel met all application requirements. The chemistry of the amine-containing polymer inhibitor and advantages of using this chemistry as a downhole squeeze product are discussed. Successful field treatment with the combined scale inhibitor and fracture fluid was conducted. A new scale inhibitor chemistry was developed for a high-temperature reservoir for combined fracture and downhole inhibitor squeeze treatments.
Abstract This paper describes results of laboratory and field testing of a solid, controlled-release scale inhibitor for use in fracturing treatments. Laboratory testing with a continuous flow apparatus has yielded inhibitor release rates under dynamic conditions. The inhibitor was tested to determine the minimum inhibitor concentration required to inhibit the formation of CaCO3, CaSO4, and BaSO4 scales in a brine. A model to predict the long-term release rate of the inhibitor was developed from data collected on the continuous flow apparatus. Data from treated wells will be compared with predictions of the model. Inhibitor release-rate testing in a continuous-flow apparatus shows that a solid, calcium-magnesium polyphosphate inhibitor has a sustained release profile. Release-rate testing shows that the inhibitor can be used up to 175 F. The inhibitor is compatible with both borate and zirconium crosslinked fracturing fluids and foamed fluids. The effective lifetime of the scale treatment can be predicted based on a model developed from laboratory data. The input variables required for the prediction include–temperature –water production –amount of inhibitor –minimum effective concentration of inhibitor for the specific brine The model can be used to aid in the design of the scale inhibitor treatment. Introduction Polyphosphate compounds were some of the first scale inhibitors used in the oil field. Phosphate esters, phosphonates (based on a variety of starting amine compounds), and polyacrylic acid-based scale inhibitors are readily available as liquids for use in squeeze treatments. The design and application of squeeze treatments have been much discussed in the literature. A carefully designed and executed squeeze treatment may provide scale inhibition for 2 years or more. P. 571