Roemex’s scale evaluation capability is as follows:
The dynamic scaling loop is designed to give Roemex the capability of modelling scale deposition at high temperatures and high pressures. Preheated brines with a tendency to form scales are mixed together in a 1mm or 0.5mm ID capillary coil, which is heated to the desired temperature. The system and coil pressures are recorded using data logging software. Chemical efficiency is relative to the degree of pressure rise; i.e. scale deposition in the capillary coil. Effective scale inhibitors will prevent or delay the crystallisation of mineral scale deposits and in turn will maintain low pressures throughout the rig.
This equipment allows scale inhibitor efficiency under reservoir conditions to be evaluated and also facilitates studies on HPHT well treatments. Chemical stability at temperature for squeeze and gas-lift applications is always a concern and with this equipment Roemex can perform efficiency tests on products to determine their thermal stability under reservoir conditions.
Two incompatible waters with the tendency to form scale are combined in a glass bottle, heated and any scale precipitated is observed. This test is primarily qualitative and gives an indication of which products are working under the scaling regime in test. The results act only as a primary selection process for removing chemicals with intolerance to the brine and those that give no protection. The test can be made quantitative by weighing the mass of scale precipitated, however a more effective means of quantifying scale inhibitor efficiency is to calculate scaling ion concentrations after any scale has formed.
Roemex recommend the testing of all products under static and dynamic conditions to obtain a product recommendation because the Dynamic scaling loop favours calcium carbonate formation over short timescales whereas the static jar test favours sulfate scaling over extended timescales.
Roemex uses the OLI Studio (previously known as ScaleChem) software package to evaluate potential and risk of different types of scale. This software allows us to quantify the likelihood and degree of scaling problems under different pressure and temperature conditions and also allows us to determine difficulties that are likely to be encountered on seawater breakthrough or when produced water streams are redirected to alternative lines, storage tanks or separators. ScaleChem software also allows us to consider the effects of changing pH and the effect of mixed phases and changes in gas composition and GOR/GLR, allowing us to scale potential at all stages of production and transport provided that appropriate data is supplied.
ScaleChem is frequently used by us to monitor the changing conditions experienced by the assets that we currently service. Any change observed in scaling potential allows us to re-evaluate the scale inhibitors and doses that are being deployed. Most commonly, ScaleChem predictions are performed following quarterly service visits. However, when large changes are detected in scaling potential, water analyses are conducted more frequently so that we can monitor the changes
Regarding squeeze inhibitor testing, Roemex currently sub-contracts core flood work.
On a quarterly basis Roemex harvest water samples from throughout the production system for 12-ion analysis at an external accredited laboratory. The data is used to build a scale prediction map and highlight the areas at most risk of scale deposition. These samples are included in the work-scope of the regular service visits to be carried out by a Roemex Engineer/Chemist.
Scale inhibitor residuals can either be performed using the Hyamine method or using an HPLC fitted with a suitable detector. Roemex regularly performs this work for existing clients.
The waxes present in most crude oils include n-alkanes, iso-alkanes, alkyl cyclic compounds and alkyl aromatics. In most crude n-Alkanes are the predominant species. The amount and distribution of these n-Alkanes is crude specific. Short-branched chains are the next most common. These have a significant impact on wax deposition characteristics.
There is no standard definition for wax content but it is generally accepted that n-alkanes from C18 to C40 represent waxy material. Paraffin solubility not only depends on the composition of the crude but also the temperature and pressure.
The wax appearance temperature (WAT) is the temperature at which, on a cooling cycle, the crude oil first precipitates solid wax. This is arguably the single most important characteristic in examining wax deposition potential in crude oil. The deposition of wax leads to several problems in reduced production and impaired flow assurance. Severe deposition can lead to loss of production and pipeline blockage etc.
The main options for removing deposits are as listed below:
Pigging – A cleaning PIG launched into a pipe to mechanically scrape wax from the pipewall and distribute it within the crude in front of the PIG.
Thermal Techniques – if the temperature of the oil can be maintained or increased above the Wax Appearance Temperature (WAT) e.g. by increasing the flow rate the wax deposits will either not be laid down or will be softened and removed.
Chemical Solvents and Dissolvers – a wide range of solvents are available, the most popular being substituted aromatics (HAN etc.) blended with gas oil. Chlorinated solvents are now precluded from use due to environmental concerns. A preferred and unique product to Roemex is RX-7492, a proprietary blend with good environmental characteristics and excellent wax dispersion and dissolution properties.
Wax Inhibitors – there are four main categories of such chemical additives:
The CSPDC allows dynamic wax deposition data to be obtained from a stabilised crude oil sample. The equipment is designed to mimic the transport of crude oil through a pipe. The shear rate experienced by the oil flowing through the pipe is calculated and applied to the crude oil which is heated to the bulk crude oil temperature. A cold finger is immersed in the crude oil and wax deposits on this surface. The equipment allows strict control of shear rates applied to the cold surface and accurate control of the temperature differential between the bulk oil and the cold surface. The equipment enables profiling of the wax deposition rate with reducing temperature to be determined in the laboratory and applied to full-scale pipelines. The technology is extremely reliable, producing wax that is very similar in composition to the wax deposits formed in the field and is our most efficient tool for evaluating products under field conditions.
The wax deposition flow loop is regarded as an industry standard and consists of a peristaltic pump, which feeds heated crude oil through a capillary coil. The coil is immersed in a cryogenic bath at an appropriate temperature (usually 4°C) to promote the precipitation of paraffin wax in the coil. The coil is attached to a pressure transducer, which records the pressure increase in the coil as the paraffin begins to deposit. Results are captured using data logging software. Inhibitor or dispersant efficiency is related to the degree by which pressure rises are suppressed; this is therefore the index to the efficiency by which paraffin deposition is inhibited.
The Haake Viscotester 550 is used to measure the viscosity and flow behaviour of crude oils and is particularly useful in characterising the effectiveness of Pour Point Depressants (PPDs) and wax inhibitors over the temperature profile of a given pipeline. The dynamic viscometer is an extremely versatile instrument giving information on viscosity, shear stress, shear rate and yield point of crude oils and chemical additives. It allows the screening of many Roemex products at different doses quickly, using relatively small volumes of oil.
Pour point tests at Roemex are based on ASTM D5853. We have made a couple of modifications to the test which are outlined in LWI-RX16. Modifications to the procedure were necessary to account for the fact that the ASTM procedure is not designed to be used for pour point depressant evaluations; it is the pour point test to be used when assaying crude oils.
Roemex does not carry out this work in-house but sub-contracts it to a commercial laboratory. Normally WAT is determined by Differential Scanning Calorimetry but can also be performed by microscopy if photographs of crystal structure are required.
Asphaltenes commonly occur through mixing incompatible hydrocarbon streams or in production tubing as the fluids reach the bubble point.
There are several techniques available to us when evaluating asphaltene deposition. The first, SARA analysis, is an Iatroscan method that determines the relative concentrations of Saturates, Aromatics, Resins and Aliphatics in a crude oil sample. From this ratio, it is possible to calculate the colloidal instability index (CII) of a crude oil, which is an indication of the oil’s tendency to flocculate asphaltenes. Roemex do not perform this in-house but send the analysis to a local laboratory.
Asphaltene inhibitor performance is evaluated at Roemex using a Turbiscan. In this test, a tube containing crude oil mixed with a light n-alkane is scaled along its length using an LED scanner which determines transmission and back scattering of the light. The apparatus can be used both in static and kinetic mode and can detect and quantify particle migration in colloidal systems. The Turbiscan software handles data acquisition and provides results, which can be graphed as % transmission against time. Samples of asphaltenic crude oil treated with dispersant are mixed with n-alkane (which causes asphaltene flocculation) and analysed. High levels of light transmission indicate that the asphaltenes have flocculated and settled out to the bottom of the tube. Low transmission indicates that the asphaltene flocs remain dispersed. The Turbiscan equipment is reliable and compact enough that it can be transported to the field if necessary.
Roemex can offer a selection of Asphaltene Inhibitors such as RX-7304 for continuous injection and asphaltene dissolvers such as RX-7020.
All water-bearing systems have the potential for microbial contamination. In general, biocides are applied to oilfield systems to control microbially induced corrosion (MIC) and alleviate the problems associated with by-products from bacterial respiration e.g. poisonous gases, inorganic and organic acids, slime and scales such as iron sulfide. Bacteria can survive as planktonic bacteria suspended in solution or as dispersed colonies or in sessile form (biofilms attached to a surface).
Frequently, oil-producing systems experience severe problems due to the growth and proliferation of bacterial populations. The most important genera of bacteria in oilfield systems are listed below with an outline of the main problems associated with their growth and proliferation:
Microbially Influenced Corrosion (MIC) by cathodic depolarisation of metal surfaces resulting in removal of the atomic hydrogen layer and the formation of localised pitting. Sulfate reducing bacteria produce hydrogen sulfide as a by-product of their metabolism which poses a significant risk to health and safety and can result in the formation of iron sulfide (pyrophoric scale) deposits. Due to their metabolic requirement for sulfate, SRB are commonly found in water injection systems (downstream of de-aeration), production systems with seawater breakthrough and crude oil / water storage vessels.
These are also implicated in the corrosion process as they metabolically secrete organic and inorganic acids which can become trapped under bacterial biofilms and promote corrosion by the removal of the passivating oxide film.
These have the potential to produce large volumes of exopolymer ideal for biofilm formation. Slime production can result in fouling and blocking of filters, lines and injection pores. Slime forming bacteria create oxygen concentration cells that can lead to under deposit corrosion and promote an ideal environment for SRB growth.
Roemex can perform microbiological testing to determine the presence of different bacterial types using test kits such as Rapidchek II and Serial Dilution using modified Postgate’s medium. Roemex can also evaluate the efficiency of biocides against different planktonic and sessile bacterial populations (single or field isolated). Roemex is able to supply a most commonly used oilfield biocides which can be deployed by batch or continuous treatment.
Hydrogen sulfide causes considerable risk to offshore staff because of its toxicity. It also contributes to corrosion and devalues the crude oil Roemex provides hydrogen sulfide scavengers for produced fluids:
Roemex can also provide oxygen scavengers for water injection and other applications. Most commonly used is RX-202 which is a sulfite based scavenger but we can also supply non-sulfite based oxygen scavengers.
Roemex has an extensive track record with supplying chemicals for the removal of oilfield deposits.
The first stage in recommending a dissolver for deposit remover is to determine the composition of the deposit. Normally we would perform some basic tests on receiving the deposit to determine its nature and more complex deposits are sent out to a commercial laboratory for further ion analysis.
Roemex can characterise generic solid types by their solubility and can provide indications as to the form of solid materials. For more in-depth analysis of solids such as scales, Roemex work with Aberdeen-based analytical companies to obtain x-ray diffraction (XRD) and scanning electron microscopy (SEM) data.
Roemex has two main scale dissolvers
Roemex can also provide dissolvers for iron sulfide and “schmoo”, halite and other types of inorganic deposit
Roemex has a number of novel non-petroleum derived wax dissolvers. These are selected and evaluated using a simple immersion wax dissolver test which can also be applied to other organic deposits.
The range of wax dissolvers includes traditional oil derived wax dissolvers such as RX-7020 and plant derived dissolvers such as RX-7492. These products are primarily used to remove waxy deposits but are also very effective against asphaltenes
With most dissolver treatments, we recommend batch treatment, soaking the affected area with dissolver with a small amount of agitation or movement at the same time. We understand that this is difficult to achieve in many situations and we have had good success with dosing our inhibitors into produced fluids. Roemex representatives can give more guidance on the best deployment technique.