Effective Scale Control Research Articles

The Effect of Production-Logging-Tool Data on Scale-Squeeze Lifetime and Management of Scale Risk in Norwegian Subsea Production Wells: A Case Study

Summary Because of the higher cost of scale management for subsea (SS) operations compared with platform or onshore fields, and because of the more limited opportunities for interventions, it is becoming increasingly important to obtain and use real production data from wells rather than estimated zone flow contribution from simple permeability (k) and height (h) models for scale-squeeze-treatment design. In this paper I discuss how scale-squeeze treatments were designed (coreflood evaluation of inhibitor retention/release) and deployed for three SS heterogeneous production wells. A permeability model and a layer-height model were initially developed for each well using detailed geological log data, estimated water/oil-production rates, and the predicted water-ingress location within the wells. Two wells were each treated three times using bullhead scale-squeeze treatments, with effective scale control being reported over the designed lifetime. A production log was acquired before the fourth squeeze campaign of these two wells. This information was incorporated into the squeeze simulation to allow review of the ongoing third squeeze and enhance design accuracy for the upcoming fourth squeezes. A third well was treated twice before production-logging data became available, and the performance of treatments to this well is also assessed. The production-logging-tool (PLT) data proved very important in changing the understanding of fluid placement and the water-ingress location during production, resulting in changes to the isotherm values used to achieve effective history match to the inhibitor returns (with PLT data incorporated in all three wells), and most significantly affecting the squeeze lifetimes. It was possible to significantly extend the treatment lifetime of two of the wells (cumulative produced water to minimum inhibitor concentration), while the treatment life of one well was greatly reduced because of the PLT-data-modified model predictions. In this paper I outline the process of reservoir/near-wellbore modeling that is used for most initial squeeze-treatment service companies deployed in the North Sea. I will highlight in detail the value that PLT data can provide to improve the effectiveness of squeeze treatments in terms of understanding of fluid placement during squeeze deployment and water-ingress location within heterogenous production wells. The intention of this paper is to highlight the value that these types of data can provide to improve scale management (squeeze treatment and water shutoff) such that the value created more than offsets the cost of acquiring such information for SS production wells.

Preproduction-Deployed Scale-Inhibition Treatments in Deepwater West Africa

Summary The injection of seawater into oil-bearing reservoirs for the purposes of maintaining reservoir pressure and improving secondary recovery is a well-established, mature operation. Moreover, the degree of risk posed by deposition of mineral scales (carbonate/sulfate) to the injection and production wells during such operations has been much studied. The current deepwater subsea developments offshore West Africa and Brazil have brought into sharp focus the need to manage scale in an effective way. In a deepwater West African field, the relatively small number of high-cost, highly productive wells, coupled with a high barium sulfate scaling tendency upon breakthrough of injection seawater, meant that effective scale management was critical to achieving high hydrocarbon recovery and that even wells at low water cuts have proved to be at sufficient risk to require early squeeze application. To provide effective scale control in these wells at low water cuts, phosphonate-based inhibitors were applied as part of the acid-perforation wash and overflush stages before frac-packing operations. The deployment of this inhibitor proved effective in controlling barium sulfate scale formation during initial water production, eliminating the need to scale squeeze the wells at low water cuts (<10% basic sediment and water). To increase the volumes of scale inhibitor (SI) being deployed in the preproduction treatments and so extend the treatment lifetimes, SI was also added to the fracturing gel used to carry the fracturing sand. This paper outlines the selection methods for the inhibitor chemical for application in fracturing fluids in terms of rheology, retention/release, and formation damage, and presents the chemical-return profiles from the five wells treated (some treatments lasting longer than 300 days), along with the monitoring methods used to confirm scale control in the treated wells. Many similar fields are currently being developed in the Campos Basin, Gulf of Mexico, and West Africa, and this paper is a good example of best-practice sharing from another oil basin.

Low Sulfate Seawater Injection for Barium Sulfate Scale Control: A Life-of-Field Solution to a Complex Challenge

Summary The injection of seawater into oil-bearing reservoirs to maintain reservoir pressure and improve secondary recovery is a well-established, mature operation. Moreover, the degree of risk posed by deposition of mineral scales to the injection and production wells during such operations has been much studied. The current deepwater subsea developments offshore West Africa and Brazil have brought into focus the need to manage scale in an effective way. To this end, the challenge of scale control during the lifecycle of water injection, production, and produced-water reinjection (PWRI) has been reviewed for a number of fields by the authors. This paper outlines the risk assessment process that should be undertaken to select the most economical and effective scale control methodology (which for sulfate-based scale could be seawater injection with scale inhibitor squeeze treatments to maintain production, or sulfate reduction of the injection water with or without the need to scale inhibitor squeeze). In the case of sulfate reduction, parameters to be investigated include the degree of desulfation required to minimize the scale risk of downhole scale formation, the impact the degree of fluid mixing will have on the resulting brine (from injection to production), and the impact the desulfated brine will have on scale control during PWRI. The paper draws on a wide range of technical inputs to make scale management decisions including: computer modeling techniques (e.g., deposition models that incorporate the kinetics of sulfate scale formation at low supersaturation ratios), reservoir simulation of fluid mixing and reaction; the resulting produced brine chemistry, laboratory-generated coreflood data to assess chemical selection for scale inhibitor squeeze and produced water application; and field results that will demonstrate the impact of the type of injection water source on the long-term manageability of such deepwater projects. Finally, the paper outlines in detail the particular issues associated with the full economic assessment of low-sulfate water injection vs. full sulfate seawater injection.

Effective scale control for seawater RO operating with high feed water pH and temperature

An effective scale control program for seawater RO is widely recognized as an important factor in ensuring trouble free and cost effective operation. This is especially important under the high feed water pH and temperature conditions found in Southern Europe and Middle East.In addition, regulatory issues concerning maximum acceptable boron levels in drinking and irrigation water necessitate the growing need to operate plants at higher feed water pH. Operating at increased pH increases boron rejection but also increases the scaling tendencies of the water. This can lead to calcium carbonate and magnesium hydroxide precipitation in the membranes.A complete scale control program needs to control calcite and brucite saturation at the maximum operating reject pH and temperature. Antiscalant chemistry, optimum dose rate as well as accurate monitoring and control of the scale inhibitor are key factors in long-term cost effective “scale free” operation.This paper details the operating strategies and scale control issues related to both single and two pass seawater RO plants operating at elevated feed water pH and temperature.

Effects of process parameters and anti-scalants on scale formation in horizontal tube falling film evaporators

In multiple-effect distillers with horizontal tubes, which are increasingly employed in seawater desalination, scale formation on the heat transfer surfaces has a highly deleterious effect on specific energy consumption and production capacity. The allowance for potential scale formation by over-sizing the heat transfer surface, scale prevention methods, cleaning methods as well as production losses during plant shutdown for cleaning create considerable capital, operating, and maintenance costs. It is therefore essential to incorporate a cost-effective scale control technique. In multiple-effect distillers scale is formed on the outside of the tubes. Mechanical cleaning methods cannot be employed. Achieving effective scale control by suitable anti-scalants is a major challenge for the desalination industry. Scale formation and control in multiple-effect distillers with horizontal tubes for seawater desalination have barely been investigated. The effects of the process parameters and of the anti-scalants on the properties of the scale, e.g., the composition, structure, and morphology, are inadequately understood. Clarifying these aspects of scale formation would facilitate further improvement of anti-scalants and thus the efficiency of multiple-effect distillers. In order to study scale formation and control under conditions that are close to those prevailing in industrial multiple-effect distillers, a horizontal tube evaporator at pilot-plant scale was employed. In the test rig the process conditions in any stage and at various operating conditions of multiple-effect distillers can be provided. Thus, the effects of the thermal field, the flow field, the fluid properties, and the substrate properties can be studied. Experiments with artificial seawater were performed at different operating conditions. Novel aspects of the formation and reduction of scales formed from falling seawater films on the outside of horizontal tubes are presented. The effects of various process conditions such as fluid temperature, heat transfer surface temperature, heat flux, and seawater salinity on the composition and structure of scale layers are shown. The beneficial effects of polymeric anti-scalants on the quantity, composition, and morphology of the scale are discussed. For example, the use of only 0.5 ppm of a specific anti-scalant effectuated a very strong reduction of the calcium carbonate content in the scale as well as a notable decline of the magnesium hydroxide content.

Special Issue

Formation damage refers to the impairment of petroleum-bearing formations by various adverse phenomena occurring in a manner to reduce the recovery of oil and gas from petroleum reservoirs. Evaluation and mitigation of formation damage in petroleum reservoirs are among the issues of primary interest for the operators in order to accomplish the economically effective production strategies during the productive life of petroleum reservoirs and to maximize the ultimate oil and gas recovery. However, circumventing the formation damage problems is a highly challenging undertaking because the formation damage phenomena involve many inherently complex interaction processes between the operation conditions and configuration of wells, the reservoir and externally-introduced fluids and particulate matter, and the constituents and conditions of the petroleum-bearing formations. This special issue presents ten papers providing information on the recent advancements made in the experimental, theoretical, and field understanding of the practical formation damage issues and the optimal measures and strategies considered for controlling and minimizing the reservoir formation damage.J. M. Schembre and A. R. Kovscek carry out laboratory core tests, apply the theory of colloidal stability, and demonstrate that high temperature, alkaline, and pH, and low salinity conditions induce fines mobilization and permeability reduction in Berea sandstones.A. Hayatdavoudi explains that the water hammer phenomenon created during the various injection and production operations may cause the sand liquefaction and production. The pressure wave-induced acceleration of the sand particles is shown to be highly sensitive to the water level variation and/or water encroachment in unconsolidated sand formations.K. J. Leontaritis presents a model for the near-well formation damage caused as a result of pore throat plugging by asphaltene particles during oil production. This model incorporates the thermodynamic-colloidal model of asphaltene in oil and an asphaltene phase behavior model for prediction of the asphaltene particle size distribution and its affect under the prevailing fluid conditions.E. J. Mackay and M. M. Jordan describe the scaling potential and formation damage due to precipitation of inorganic scales during conventional waterflooding in deepwater regions associated with the offshore production environments. The various risk management strategies for effective scale control are reviewed by means of reservoir simulation.H. A. Nasr-El-Din discusses the measures required to minimize and control the various formation damage problems caused by the common chemical treatment techniques originally designed to remove the particular formation damage problems.C. Li, T. Xie, M. Pournik, D. Zhu, and A. D. Hill apply a fine-scale model for the sandstone core acid flooding process by numerically solving the acid and mineral balance equations for a three-dimensional flow field. The reservoir heterogeneities are shown to cause the acid to penetrate much farther from the injection face into the formation than for a homogeneous case.G. Penny, J. T. Pursley, and D. Holcomb demonstrate by laboratory core tests and field examples that a new microemulsion additive helps for effective cleanup of injected fluids in tight gas formations. The applications involving the remediation and fracture treating of coals, shales, and sandstone reservoirs result in lower formation damage and higher production rates.D. B. Bennion and F. B. Thomas review the formation damage mechanisms associated with very low in-situ permeability gas reservoir formations, emphasizing on the relative permeability and capillary pressure effects leading to phase trapping. The challenges encountered during the drilling and completion practices in order to minimize the impact of formation damage on the well productivity are described.H. Jahediesfanjani and F. Civan investigate the damage tolerance of the conventional well-completion and stimulation techniques in reducing the formation damage effects and increasing the productivity of the coalbed methane reservoirs. The efficiency and performance of the openhole cavity completions, hydraulic fracturing, frack and packs, and horizontal wells are compared with a nondamaged vertical well in terms of the normalized productivity index.Y. Ding and G. Renard present an integrated approach for evaluation of the performance of oil and gas wells after drilling induced formation damage by means of a near-wellbore modeling using the input data obtained by laboratory tests.

Impact of Brine Flow and Mixing in the Reservoir on Scale Control Risk Assessment and Subsurface Treatment Options: Case Histories

As offshore production environments become ever more complex, particularly in deepwater regions, the risks associated with formation damage due to precipitation of inorganic scales may increase to the point that production by conventional waterflooding may cease to be viable. The ability to predict and control such formation damage can thus become critical to project success under such circumstances. The work described in this paper presents how the risk may be managed from early in the CAPEX phase of projects through to the OPEX phase by use of reservoir simulation tools to better understand the scaling potential in a reservoir and the possibilities for effective scale control. This process is illustrated by reference to a number of field examples where specific scaling problems have been identified, and the ability to implement effective scale management has been impacted by detailed fluid flow and brine-mixing calculations.

THE CONTROL OF MANGO SCALE IN COMMERCIAL ORCHARDS THROUGH THE USE OF THE PREDATORY BEETLE, CYBOCEPHALUS BINOTATUS

Mango scale insect, Aulacaspis tubercularis Newstead, is a major pest in South African mango orchards. Chemical control using organo-phosphates is effective but is not conducive to an IPM pest management system. Cybocephalus binotatus Grouvelle, a predatory beetle of mango scale was introduced into South Africa in 1995 and has since become well established in the mango growing areas. The effectiveness of this predator in controlling mango scales was investigated during the 1999/2000 mango season. A retrospective study of past Cybocephalus releases, trials carried out in insect-proof tents and large field trials revealed that the predator successfully controls scale populations to levels of 2-3% scale infestation. The beetles are mass feeders and require a substantial scale population in order to sustain themselves. Female predatory beetles were found to produce only as many offspring as the scale population could support. Furthermore, the field trials indicated that the rate of scale population decline was somewhat independent of the number of predatory beetles released and remained reasonably constant. For effective scale control it is recommended that between 500 -1000 beetles be released per hectare of cultivated mangoes.

Evaluation of various additives at Jubail phase I during reliability trials

Jubail Phase I consists of 6 dual purpose units, each having a boiler, turbine and desalination unit. Total design output is 30.06 mIgd of distillate and 360 MW of power, each desalination unit designed to produce 5.01 mIgd at maximum brine recycle temperature of 90.6°C using polyphosphate as the scale control additive. Long operating experience with polyphosphate [1] showed it to be a moderately effective scale control additive. It was decided to evaluate other additives available on the market, compare their effectiveness for scale control, and to conclude which one would give longest operating time before the plant performance ratio drops necessitating acid cleaning. Belgard EVN was employed as the scale control additive during commissioning and reliability trials of unit Nos. 1 and 3. Albrivap B and Flocon 247 were used on unit Nos. 2 and 4, respectively. This paper presents experience with these additives during the first four reliability trials.

An Evaluation of Scale Inhibitors

A rating of inhibitors in the order of their effectiveness is a relative matter and depends upon test conditions. The most important conditions are the degree of supersaturation and the temperature; the higher the supersaturation and the higher the temperature the less effective a scale inhibitor becomes. Scale Inhibition Is Still an Art Scale inhibition is still closer to being an art than a science. The literature deals only to a very small extent with the problems of scale inhibition. Most of the published data do not consider the basic facts of crystallization and inhibition. such as reaction mechanisms and kinetics. Because these fundamental considerations are often neglected, there are many recorded failures of scale treating procedures in oil and gas fields. This neglect of fundamentals and lack of data is surprising because the formation of scale is a rather costly problem for some industries, above all the petroleum industry. We lose many millions of dollars petroleum industry. We lose many millions of dollars in revenue every year because scale creates flow restrictions in our fields. Accurate evaluation of scale inhibitors is the first and most important step toward effective scale control. How Are Scale Inhibitors Presently Tested? Presently Tested? Test Machines Several investigators have been concerned with the development of test machines designed to simulate the conditions of scale deposition in the field. The degree of scale buildup in these test devices is used to screen and rank commercial products and experimental chemicals. Scale Coupons The use of scale coupons in the field is a test somewhat related to the use of test machines in the laboratory. Steel coupons are inserted in flow lines, and the amount of scale they accumulate is used to evaluate an inhibitor that has been injected into the system upstream of the coupon. Precipitation Test Precipitation Test In the "chelation test," which should be called the precipitation test, two chemically incompatible precipitation test, two chemically incompatible solutions are combined. The precipitation of scale-forming solids - for example, calcium carbonate (CaCO ), calcium sulfate (CaSO,) or barium sulfate (BaSO ) is measured in the presence of an inhibitor of varying concentrations by means of chemical analyses. The amounts of precipitate obtained are then compared with the amount of precipitate formed by mixing solutions containing no scale inhibitor. The more solids that are kept in solution by a given amount of inhibitor. or the less inhibitor that is needed to keep a given amount of solids in solution, the more effective and desirable the inhibitor is thought to be. This test is widely used for laboratory evaluation of scale inhibitors. The test is very quick and convenient to run, gives fast results, does not require costly equipment, and can be run by relatively untrained personnel. Unfortunately, the reproducibility of the result is sometimes very poor, and data reported by different testers is often contradictory. P. 997

Comparative Tests with Dormant Sprays for San Jose Scale Control

A record of outstanding results obtained for three years (1921-1923) with lime-sulphur and oils as dormant sprays for the control of the San Jose scale, Aspidiotus perniciosus Comst., Lime-sulphur did not give a sufficient kill to check the scale, which corroborated the results obtained by commercial orchardists in southern Indiana. Lime-sulphur is still an effective scale control in most sections of northern Indiana. Dry lime-uslphur was about as effective as the liquid concentrated provided it was used at one and one-half to two times the strength recommended by the manufacturers. Under conditions existing the past few years in most of southern Indiana, the oil sprays are the only ones which have given satisfactory control. These include the miscible oils, petroleum soaps, and oil emulsions. The summer use of oil emulsion cannot be recommended to take the place of a dormant spray although under certain conditions a summer application materially assists in checking scale.1