Predicting Carbonate Scale in Oil Producers from High Temperature Reservoirs

Ramstad, Kari; Tydal, Trine; Askvik, Kjell Magne; Fotland, Per

doi:10.2118/87430-ms

Cited by 11 publications

(4 citation statements)

References 8 publications

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“…Often used critical values for calcite are an SR between 2 to 3, for BaSO 4 an SR between 5 and 10 and for SrSO 4 an SR of 2 to 5. Ramstad et al 3 have recently shown that the critical SR for calcite is much lower than 2 for wells where the temperature is >100 o C.…”

Section: Scaling Calculationsmentioning

confidence: 99%

Downhole Scale Management in Gorm, Dan, and Halfdan, and Implications to Industry Trends

2006

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TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThree oil producing fields in the Danish sector of the North Sea, Gorm, Dan and Halfdan, have been assessed for downhole scale control. All three fields have water injection. To date downhole scaling has not been perceived as a significant production problem in these fields. This paper presents the results of a review of the well service history for each well in the three fields which identified when and where scales had been encountered and estimated the impact of scale on well intervention operations. A thermodynamic equilibrium model for mineral solubilities was used to assess the scaling tendencies of sulphate and carbonate scales from bottom hole to wellhead. The observational data for downhole scale has been compared with the scaling predictions and a risk assessment for carbonate and sulphate scales developed for each well. The implications of this study on industry trends are discussed.

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Section: Scaling Calculationsmentioning

confidence: 99%

Downhole Scale Management in Gorm, Dan, and Halfdan, and Implications to Industry Trends

2006

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“…Relatively high reservoir temperature (124 °C) combined with pressure drop in the wellbore has caused calcium carbonate scale to form in the upper tubing, affecting operation of DHSV (540 m MD) (Ramstad et al, 2005). The Oseberg Øst field consists of deviated and horizontal wells producing from the Brent group reservoirs and the drive mechanism is gas and water injection (Utsira aquifer and produced water).…”

Section: Scaling Of Production Intervals Due To Incorrect Inhibitor Pmentioning

confidence: 99%

Squeeze Related Well Productivity Impairment Mechanisms & Preventative/Remedial Measures Utilised: Norwegian Continental Shelf

Fleming¹,

Ramstad²,

Mathisen³

et al. 2010

Proceedings of SPE International Conference on Oilfield Scale

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Squeezing is routinely employed by Statoil as a means of maintaining well productivity and avoiding safety issues related to downhole safety valve scaling. In the majority of cases, squeezing maintains well production through minimisation of scale related downtime. However, it has been observed occasionally by Statoil that the benefits of scale prevention by squeezing can be outweighed by the detrimental impact on well productivity. While there have been several articles covering specific elements of a squeeze operation that have affected well productivity, little has been published that attempts to completely describe squeeze related, production impairment mechanisms. This paper will aim to address this gap by demonstrating how squeezing, in some cases, can have an adverse impact on well productivity and highlight the remedial or preventative methods that have been utilised.A review of the squeeze related, production impairment mechanisms from Statoil operated fields show that they can be related to near wellbore formation, alteration in the reservoir production characteristics or completion design. Physical formation damage mechanisms include a. Squeezing of sensitive reservoirs (fines mobilisation and clay swelling) b. Scaling of production intervals due to incorrect inhibitor placement c. Viscosified inhibitor formation damage d. Damage related to precipitation squeezes e. Increased sand production after squeezing Liquid formation damage mechanisms include a. Squeeze related relative permeability alteration causing increased water cut and reduced oil rates. b. Water blocks and emulsion formation due to squeezing of an aqueous treatment into an oil producing or water sensitive interval. Other examples of squeeze related productivity impairment are screen and gravelpack blockage while an indirect effect are lift problems after squeezing in wells with depleted reservoir pressure. In all instances, the economic costs of lost production can far exceed those of actually performing the squeeze. Case histories will be used to illustrate the productivity impairment mechanisms and methods used to overcome these along with lessons learned.

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“…SR of 2 at 98°C. 4 Other work suggests that an SR of 5 may be required for calcium carbonate precipitation at 80°C, whereas this drops to 1.2 at 150°C. 5 Thus given that a brine system is at equilibrium in the reservoir, during production at elevated temperatures only very small perturbations in the equilibrium of the brine chemistry, by pressure changes during production or re-distribution of water and / or carbon dioxide between the different phases, can rapidly lead to precipitation of scale, whereas such small changes in more a less severe (lower temperature) environments may not represent a scaling problem.…”

Section: Introductionmentioning

confidence: 98%

Scale-Dissolver Application Under HP/HT Conditions -- Use of an HP/HT "Stirred Reactor" for In-Situ Scale-Dissolver Evaluations

Williams¹,

Wat

Chen³

et al. 2005

All Days

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In several high temperature and high pressure (HT/HP) production environments severe downhole carbonate scale formation is often anticipated and effective carbonate scale dissolvers are required. However for most cases the selection of scale dissolvers is conducted under much less severe conditions, involving simple bottle tests conducted at temperatures up to 95 o C and ambient pressure. These tests although generally accepted for screening purposes suffer a number of significant limitations. In addition to the moderate test conditions the low pressure means that carbon dioxide is readily released following the dissolution and results in changes in the test pH which may mean the efficiency of the dissolvers could be overstated. This paper describes the use of a novel a novel HP/HT "stirred reactor" test rig to more closely examine the relative performance of selected scale dissolvers including organic acids (formic and acetic acids), inorganic acids (16% HCl) and other more conventional scale dissolvers under typical field application conditions. The equipment is specially designed for the extraction and stabilisation of samples at or 'near' tested conditions and therefore allows the equilibrium dissolution level to be determined under more representative HP/HT conditions.In this work preliminary tests were conducted using 16% HCl under progressively more severe test conditions (RT & 1,500 psi; 150 o C & 1,500 psi and then 150 o C & 4,500 psi. Further tests were then conducted to compare the performance of organic acid based scale dissolvers (formic acid and acetic acid based products) together with other selected scale dissolvers at 150 o C and 4,500 psi and compared with the results obtained for 16% HCl. For these HP/HT tests, samples were collected and analysed after 2 and 20 hours equilibration time and results were compared with those obtained in more conventional "bottle tests conducted at less severe environmental conditions (90 o C and ambient pressure).In summary the results demonstrate the importance of conducting scale dissolver tests for field applications under more representative (HP/HT) conditions.Of particular significance was the impact of the cooling and pressure reductions. For one of the products tested, although very good dissolution was recorded under the HP/HT conditions, reprecipitation of a different polymorph of calcium carbonate occurred very rapidly resulting in a significant increase in the volume of carbonate precipitation within the reaction vessel and various sample lines. The paper will describe the details of the test equipment used in this work and present a mechanistic interpretation of the various results obtained. TX 75083-3836, U.S.A., fax 01-972-952-9435.

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Predicting Carbonate Scale in Oil Producers from High Temperature Reservoirs

Cited by 11 publications

References 8 publications

Downhole Scale Management in Gorm, Dan, and Halfdan, and Implications to Industry Trends

Downhole Scale Management in Gorm, Dan, and Halfdan, and Implications to Industry Trends

Squeeze Related Well Productivity Impairment Mechanisms & Preventative/Remedial Measures Utilised: Norwegian Continental Shelf

Scale-Dissolver Application Under HP/HT Conditions -- Use of an HP/HT "Stirred Reactor" for In-Situ Scale-Dissolver Evaluations

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