The advent of wells with extremely long producing intervals, extended-reach and multilateral wells, typically completed in heterogeneous formations, brings with it challenges regarding completion design to maximize overall production in a sustained manner. Judicious placement of Inflow Control Devices (ICDs) can ensure a more even inflow of fluids along the full length of the interval, delaying water or gas breakthrough and in some cases restricting water production. Such devices also influence the placement of chemical treatments, such as scale-inhibitor "squeeze" treatments, which in turn affects the subsequent treatment lifetimes and efficiency.
This paper presents a new analytical model to explicitly simulate the effect of ICDs on squeeze treatments and, in particular, on treatment placement and consequent lifetimes. The explicit method of modelling ICDs, which is based on Bernoulli's theorem of constricted flow through a pipe, is compared with other implicit phenomenological approaches, such as modelling the effect of an ICD as a damaged region using a dual-permeability model. By this comparison, the relevance of dual permeability modelling for simulating ICDs is presented. The relationship between chemical placement and inhibitor return has been clearly demonstrated in other publications (
In summary, the paper describes the development of an important new tool to assist in the design of optimum chemical treatment strategies in wells completed with ICDs, without the need to use more complex reservoir simulators for near-wellbore treatment in complex completions.
To develop scale management strategies and plans during field development planning, it is important to know the composition of formation water in the reservoir. Typically, formation water samples will be collected from appraisal wells and analysed for this purpose. However, when the wells are drilled with water-based mud, the samples are often contaminated with mud filtrate that has invaded the formation during drilling. By adding a tracer to the drilling mud and using a simple mass balance correction technique, it is possible to correct for the effects of contamination and obtain an estimate of the formation water composition. But, where reactions occur during invasion or within the sample after collection, this method of correction will generate an erroneous estimate of the composition. The errors will increase with the extent of reaction and degree of contamination.
In this paper, we describe a new ‘correction’ approach which additionally makes use of (a) 1-D reactive transport modelling of mud filtrate invasion and (b) modelling of reactions occurring in formation water samples after collection. This approach accounts for the potential effects of these reactions and provides an estimate of the formation water composition within uncertainty limits. It reduces the risk of obtaining erroneous estimates of formation water composition and is particularly beneficial where reactions occur and where the mud contamination fractions are elevated (e.g. ~10-40%). At higher fractions, the uncertainties can be so high that the estimated compositions are not useful, emphasising the risks of trying to estimate formation water compositions from heavily contaminated samples.
This approach has been applied to formation water samples obtained from the Nova Field (formerly Skarfjell, Norwegian North Sea). It has meant that the resulting composition and associated uncertainties have been used with more confidence in scale management planning; to select seawater as the injection water, and to identify the scale risks across the relevant nodes in the production process over the life of field of the asset. Based on these risks, appropriate scale mitigation and monitoring measures have been selected.
The formation of silica and silicate scales caused troublesome issues in various water-handling systems, including steam generators, geothermal wells, and waste-water disposal systems. Recently, a produced water with over 300 ppm of silica, and a spent brine off the strong acid cation (SAC) softeners containing high levels of calcium (Ca), barium (Ba), and magnesium (Mg) were commingled in the production wells. The mixing of these two waters induced silicate as well as other scales, including calcite, barite, etc. In order to provide effective scale inhibition when these waters are mixed, effective scale inhibitors for both silicate and other scales were requested for evaluation.
In this paper, scale inhibitor chemistries for preventing both silica/silicate and other scales were reviewed and the possible synergistic effects were assessed by Design of Experiment (DOE) software. DOE is a systematic method to determine the relationship between several factors, i.e. various chemistries and the performance of formulations under designed application conditions. Selected chemicals were formulated for control of both silica/silicates and other scales, and their performances were evaluated by a Kinetic Turbidity Test (KTT). The KTT is a novel laboratory test method using an Ultraviolet-Visible (UV-Vis) spectrophotometer to monitor the formation of scales at various dosages of tested products. Bottle tests were also conducted for the comparison of inhibition performance.
Based on the lab testing results from the KTT and the bottle tests, the combined products exhibited good scale inhibition performance for both silicate and other scales. The product was recommended for field applications. Subsequent field applications of this product have provided the desired scale control.
This paper presents the laboratory testing data for scale inhibitor selection for the combination products on both silica/silicate control and other scale control by using the efficient performance evaluation method. It also provides an effective product formulation approach for finding synergetic effects of different products. Successful scale inhibitor implementations in the field applications are also presented in this paper. Both laboratory and field testing results show a good case history for the optimization of the silica/silicate and other scale treatment.
Scale prediction in downhole scenarios is somewhat complex due to the large range of variables that drive inorganic precipitation. While the reservoir fluid flow ascendant into the wellbore it passes through many different completion equipments such as downhole valves. In the scope of oilwell completion design, a typical wellbore configuration takes into account two or three intervals, so a selective completion is required. In this way, Sliding Sleeve Valves (SSV) are normally employed together with packers to allow the production selectivity. Despite the positive aspects of this arrangement, the turbulence, the change in the flow trajectory into the valves and the considerable pressure drop can generate a friendly environment for the occurrence of calcium carbonate (CaCO3) scale. The pressure drop in this tool induces the flash liberation of CO2 from the aqueous solution and consequently, the chemical equilibrium, which controls the precipitation of CaCO3, is displaced towards the direction of precipitation of this solid in the flowing stream. Through the computational fluid dynamics technique (CFD), this work aims to study the effect of geometric variables of a generic downhole valve and the effect of the influx flow rate and fluid properties on the minimization of the overall pressure differential in the valve. Through the discrete phase modeling (DPM), the effect of the flow intensity on the transport of the solids to the internal adhesion surfaces is verified, and which of these surfaces are more favorable to the scaling phenomenon. By comparative analysis, it is shown that the volumetric influx rate is the most significant factor in the pressure drop (response variable). For the geometric factors, the effect of the number of connections between the annular outer region and internal tube presented a greater relevance compared to the chamfer angulation effect considered at the inlet of these connections.
Ma, Xiaoguang (Norwegian University of Science and Technology) | Neteland, Marte (Norwegian University of Science and Technology) | Broby, Margrethe (Norwegian University of Science and Technology) | Andreassen, Jens-Petter (Norwegian University of Science and Technology) | Seiersten, Marion (Institute for Energy Technology)
Monoethylene glycol (MEG) regeneration may include a pre-treatment to reduce the concentration of cations that tend to induce scaling in the downstream process. This work reproduced pre-treatment conditions in a continuous stirred-tank reactor. The experiments were performed in 50 wt% MEG solutions at 80°C. Divalent cations and alkalinity solutions were dosed into the reactor and the mixed solution was pumped out at controlled rates. Steel rods were inserted into the test solution to measure scaling rates. The growth of scale and particles in bulk solution with varying Mg2+, Fe2+ and SO42− ions were studied as function of supersaturation with respect to calcite.
The experimental results show that crystallization fouling, rather than particulate fouling, is the dominating mechanism controlling the formation of calcium carbonate scale in MEG pre-treatment. The supersaturation at steady state controlled the amount of scale. The presence of Mg2+ retarded the nucleation rate of calcium carbonate and thereby lowered the surface areas available for consumption of Ca2+ and CO32− in in the bulk solution. It resulted in higher CaCO3 supersaturation which promoted scaling. Addition of Fe2+ had little effect on scale formation. At these conditions, the calcium carbonate scale that formed on steel rods and as solids in the bulk were exclusively the aragonite polymorph. Seeding with aragonite reduced the scaling tendency in the experiments where Mg2+ was present. The result indicates that maintaining a large active surface area for growth in the bulk solution can reduce the scale formation.
Di Toto, Raul Antonio (Italmatch Chemicals) | Bruyneel, Frederic (Italmatch Chemicals) | Parravicini, Davide (Italmatch Chemicals) | Kan, Amy T. (Rice University) | Tomson, Mason B. (Rice University) | Yan, Fei (CETCO Energy Services)
The paper describes the development of the first readily biodegradable - in seawater - phosphonated amino acid chemistry (PHAAC), which is able to control calcite and calcium sulphate scale under unconventional HTHP1 conditions (simulated Shearwater field conditions and T/P up to 250°C/1,000bar). This novel chemistry is aimed to support unconventional and ultra HTHP productions in a cost-wise sustainable manner.
The chemistry development is described from the selection of the suitable chemical functionalities through the evaluation of the "must have" properties – brine compatibility, thermal resistance, eco-toxicity profile – to the assessment of performance for calcite, calcium and barium sulphate by dynamic and static scale inhibition tests under uniquely severe conditions (T= 55°C-250°C, salinity = max. 250,000ppm, Calcium = max. 18,960ppm). Successful squeeze simulation was tested at high temperature with a high Ca connate water. Software simulations - Pitzer electrolyte theory - were used to preliminary screen out and define conditions.
The novel chemistry, when compared to industry benchmark inhibitors from low (55°C) to ultra high temperature (250°C), showed an extremely positive overall performance gap. The product thermal resistance evaluation and its impact on chemical stability, properties and performance, is presented showing that stability of the chemical structure - only 1.3% degradation after 7 days at 160°C - eliminates the performance drop when conditions get severe. Minimum inhibitor concentration of the novelty chemistry is up to 10 folds less than conventional chemistries in dynamic scale rig tests and squeeze life is excellent, allowing remarkable cost saving in treating scale in extreme conditions. Detrimental effect of Fe++ on performance and chemical compatibilities are also assessed. Negligible toxicity against marine species and readily biodegradability in seawater makes the chemistry suitable for offshore operations in OSPAR countries. Presented results coupled to ease of detection proof that the new experimental environmentally friendly scale inhibitor can be successfully deployed in HTHP applications for the control of calcium carbonate and calcium sulphate under extremely severe regimes.
The novel chemistry is the first readily biodegradable (OECD306) phosphonate for scale inhibitor applications in HTHP unconventional conditions. It sets new levels of performance in the control of frequently encountered scale types in O&G. The documented inhibitor properties and performance, confirm that it can be a game changer for flow assurance strategies in unconventional productions.
Produced waters are increasingly found to contain high levels of dissolved iron, with typical ferrous iron concentrations ranging from a few ppm to several hundred ppm. The presence of iron can cause issues in production, one problem being a detrimental effect on the performance of scale inhibitors. The aim of this work was to investigate scale inhibitor chemistries with improved iron tolerance, and apply a new product in the field to address a severe inorganic scale issue that had been encountered.
Using static bottle tests to assess brine compatibility and anaerobic dynamic scale loop tests to assess scale inhibition efficiency, a wide variety of scale inhibitor chemistries containing different functional groups were screened. The aim was to identify an inhibitor which would give the best performance against calcium carbonate scale in the presence of up to 100ppm Fe2+. Previous studies have shown that the inhibition of calcium carbonate scale is more adversely affected by the presence of iron than the inhibition of barium sulfate scale, and as calcium carbonate was the main challenge in the field case the emphasis was placed on inhibiting this scale type.
Initial compatibility studies revealed the additives with the best brine compatibility, and around nine additives were taken forward for performance testing. It was found that acrylic acid based copolymers demonstrated reasonable scale control at 5-20 ppm Fe2+, but at higher iron the high dose levels required meant that the limit of compatibility was reached before complete scale control had been achieved. The best performing additive for calcium carbonate was found to be a phosphonate derivative. A field trial was conducted in a predominantly calcium carbonate scaling environment as a proof of concept and scale inhibitor residuals were monitored over a 5-month period. After this successful study, further lab experiments were performed with the chosen inhibitor to demonstrate good calcium carbonate control in the presence of up to 100 ppm Fe2+.
A comprehensive investigation of different scale inhibitor types resulted in an optimum chemistry to control calcium carbonate scale in the presence of high concentrations of ferrous iron. Applying this chemistry in the field has demonstrated better scale control than was being achieved with the previous scale inhibitor.
Steamflooding technology introduction into hydrocarbon recovery operations often brings with it unwanted unavoidable mineral scaling challenges. In this example, steamflood generated calcium carbonate scale caused downhole equipment failure during cyclical steamflood stimulation (CSS) operations. The precipitated scale was effectively removed via mineral acid tubing wash, however mineral acid use for ad-hoc scale dissolving duty added significantly to the corrosion burden of well production tubing strings already regularly exposed to aggressive high concentration mineral acid during near wellbore matrix stimulation treatments. Scale inhibitor squeezing was proposed as a proactive alternative to mineral acid for downhole scale mitigation, and is the subject of this case history. The Middle Eastern heavy oil (HO) field has experience in employing scale inhibitors for topside scale control, but has limited experience in scale squeezing, and no experience of scale squeezing cyclical steam flooded wells. The initiative therefore presented some interesting challenges with respect to the Scale inhibitor selection (thermal stability concerns, compatibility and calcium carbonate efficacy concerns), where to place the scale squeeze in the CSS treatment programme, the squeeze design and its placement within the CSS well, and introduction and execution of routine well scaling health monitors for assessing the performance of the scale squeeze across the full CSS life-cycle.
Detailed bullheaded scale squeeze designs were prepared for two pilot HO field CSS wells that had experienced CaCO3 scaling. Once prepared, the squeeze treatments were quickly scheduled and executed without significant issue - either during treatment application or post-squeeze/steamflood return. The well brine monitors (brine ion composition, residual scale inhibitor and suspended solids) revealed interesting trends during the surveillance phase, but most importantly showed that the scale squeezes performed according to design and successfully maintained the wells free of CaCO3 scale, up to and including the 266 days post-steamflood, at which point routine well produced water sampling was discontinued. After 360 days (at the final review meeting) the field operators advised that both squeezed wells were still in operation and had experienced no scaling downtime.
Reliable and accurate analysis of inhibitors is vital for decisions on efficiency and cost-effectiveness of scale inhibitor squeeze treatments. Recent developments have resolved issues for residual sulphonated polymer chemistries which were previously difficult to isolate. Attention now is directed to challenges associated with phosphonate based inhibitors, particularly when assay is required from a multi-component produced water sample containing other P based inhibitor species which currently poses a significant challenge.
This paper describes the advantages and limitations of techniques used for phosphorus assay including inductively coupled plasma spectroscopy, ion chromatography and wet chemical methods (e.g. Phospho-molybdenum blue, PMB) approaches. Field examples are discussed to emphasize the analytical challenge with cases whereby speciation is readily achieved and others where this is not the case.
To overcome the limitations of these methods, novel approaches for analysis of P – containing inhibitors (in the presence of other –containing additives) include time resolved fluorescence spectroscopy (TRF) and mass spectrometry (MS) detection (which also require development) are considered with potential benefits and limitations / interferences highlighted. These are discussed with highlights of TRF development presented. This technique shows significant scope and potential with promising results showing speciation and discrimination of both polymeric and phosphonate based scale inhibitors as well as a phosphate ester based corrosion inhibitor.
This paper highlights the concept that for residual scale inhibitor assay, one analytical approach does not fit all environments and applications. However the availability of a range of techniques, some of which are still in development, allows for effective monitoring in complex, multi-component environments. The paper highlights development opportunities for some of the newer approaches such as TRF and MS as well as discussing their limitations in complex produced fluids.
Zhu, Da (RGL) | Gong, Lu (University of Alberta) | Qiu, Xiaoyong (University of Alberta) | Hu, Wenjihao (University of Alberta) | Huang, Jun (University of Alberta) | Zhang, Ling (University of Alberta) | Fattahpour, Vahidoddin (RGL) | Mahmoudi, Mahdi (RGL) | Luo, Jing-Li (University of Alberta) | Zeng, Hongbo (University of Alberta)
The scaling has been found to be a major problem in thermal production, such as in the Steam-Assisted Gravity Drainage (SAGD) operation. In addition to providing a favorite environment for corrosion, scaling could result in extreme plugging in sand control devices. Therefore, any coatings for the equipment and completion in thermal production should provide significant anti-scaling surface properties.
This paper presents a detailed study, including field and laboratory testing, on application of the Electroless Nickel Coating (EN-coating) in thermal production environment. Initially, EN-coated and uncoated carbon steel samples were tested in laboratory to assess the scale, hardness and adhesion of inorganic and organic materials.
Successful laboratory testing lead to a field testing plan, which involves deploying the EN-coated and uncoated samples into a horizontal well for thermal production. The specimens were recovered after certain time and a comprehensive X-ray Photoelectron Spectroscopy (XPS) and Energy-Dispersive Spectroscopy (EDS) were performed to assess accumulation of fouling substances on EN-coated and uncoated carbon steel.
This study suggests the application of the EN-coating technology to solve the problems caused by scale, and adhesion of organic and inorganic material in thermal production. The comprehensive laboratory testing and field data from the SAGD wells shows that EN-coating significantly improves the well integrity in the harsh thermal production environment.