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Development Of Low Corrosive Environmental Friendly Calcium Carboante Scale Dissolver For HTHP Wells
Chen, Tao (Champion Technologies Peterseat Drive) | Chen, Ping (Champion Technologies Peterseat Drive) | Montgomerie, Harry (Champion Technologies Peterseat Drive) | Hagen, Thomas (Champion Technologies Peterseat Drive) | Juliussen, Bjorn (Champion Technologies) | Haaland, Torstein (Champion Technologies)
INTRODUCTION ABSTRACT Calcium carbonate is one of the most common scales found in oilfields. Scale inhibitor treatment is a traditional method to control the calcium carbonate deposition. Scale acid treatment is another common way to remove/dissolve carbonate scale. However, high corrosion rate of scale dissolvers at high temperature and the environmental requirement for scale dissolvers have been two major challenges in the development of scale dissolvers and applications under HTHP conditions. In this paper, a low corrosive environmental friendly calcium carbonate scale dissolver has been developed to provide a treatment to remove calcium carbonate scale formed in HTHP wells. The characteristics of this product are as following: Yellow Y1 environmentally acceptable chemical in Norway. Both the aged (170°C) and non-aged samples showed similar CaCO3 dissolving capacity. A high dissolving rate in the initial stages of scale dissolution. No re-precipitation risk after cooling. · Low corrosiveness at temperatures up to 170°C. General corrosion is low and no pitting corrosion observed.In addition, a winterized version of this dissolver has been developed. The performance tests have been carried out and reported as well. Calcium carbonate, CaCO3, is one of the most common scale depositions found in oilfield production wells and surface facilities. It can be deposited all along the water paths from injectors through the reservoir to the surface equipment, especially in high temperature and high pressure (HTHP) wells, where temperature is up to 250C and pressure is up to 20000psi. Calcium carbonate scale forms when the solution is supersaturated with respect to Ca ions and HCO3 -ions. The two major factors causing CaCO3 deposition in the oil and gas industry are reduction in pressure and high temperature during production. Pressure drop leads to the loss of carbon dioxide (CO2) from aqueous solution. This causes an increase of pH and an associated increase of supersaturation. High temperature is another driving force causing CaCO3 self-deposition. The solubility of calcium carbonate decreases with temperature increase, hence CaCO3 crystallization frequently occurs at high temperature. In addition, the kinetics of calcium carbonate scale formation is a function of temperature, i.e. slow kinetics at low temperature. As the temperature increases, the formation of calcium carbonate will accelerates and precipitation may occur at an earlier stage. Carbonate scale formation can impair production by blockage of tubing and flowlines, fouling of equipment and concealment of corrosion. The effects of carbonate scale can be dramatic and costs can be enormous. Effective techniques are needed to solve the scale deposition and keep producing wells healthy. In most cases, scale prevention through chemical inhibition is the preferred method of maintaining well productivity. In order to minimize the formation of scale deposits, scale inhibitors treatment with polycarboxylates or phosphorous containing compounds (such as phosphonates or phosphate esters) are common practice in oil industry. However, while the most polymer scale inhibitors showed a good thermal stability, some phosphonate inhibitors had a limited usage for being applied at temperatures over 170C.
- Europe > United Kingdom (0.47)
- North America > United States > Texas (0.29)
- Europe > Norway > Norwegian Sea (0.24)
- Materials > Chemicals (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Water & Waste Management > Water Management > Constituents > Salts/Sulphates/Scales (0.75)
Scale Dissolver Application Under HP/HT Conditions - Use of a HP/HT "Stirred Reactor" for In-Situ Scale Dissolver Evaluations
Williams, Helen (Scaled Solutions Limited) | Wat, Rex Man Shing (Statoil ASA) | Chen, Ping (Champion Technologies Ltd.) | Hagen, Thomas (Champion Technologies Ltd.) | Wennberg, Kjell Erik (Statoil) | Vikin, Vigdis (Statoil) | Graham, Gordon M. (Scaled Solutions Limited)
Abstract 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 95ºC 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; 150ºC & 1,500 psi and then 150ºC & 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 150ºC 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 (90ºC 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, re-precipitation 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. Introduction The development of HP/HT gas condensate fields in the North Sea has brought about a number of important oilfield scale control problems.These fields are often characterised by temperatures in excess of 150ºC, downhole pressures of greater than 10,000 psi and high salinity brines (TDS > 200,000ppm).1In several of these HP/HT fields severe downhole carbonate scale is anticipated during production due to changes in the temperature, pressure and pH which lead to changes in the supersaturation of calcium carbonate in the brine.Pressure reduction during production is one of the main causes of carbonate scale formation due to the evolution of carbon dioxide from the brine phase, which increases the solution pH (Equation 1) and the solubility with respect to carbonate declines rapidly, leading to precipitation (Equation 2).
- North America > United States > Texas (0.28)
- Europe > United Kingdom > North Sea (0.24)
- Europe > Norway > Norwegian Sea (0.24)
- (3 more...)
Creating Value with Green Barium Sulphate Scale Dissolvers - Development and Field Deployment on Statfjord Unit
Børeng, Raymond (Statoil) | Chen, Ping (Champion Servo) | Hagen, Thomas (Champion Servo) | Sitz, Curtis (Champion Servo) | Thoraval, Rozenn (Champion Servo) | Kotlar, Hans Kristian (Statoil)
Abstract The Statfjord oil field, operated by Statoil in the North Sea, is far down its production decline curve. 60% of the STOOIP has been recovered during the past 24 years of production with secondary recovery techniques, leaving complex distributions of by-passed oil reserves, water and gas. In order to maintain cost-effective production of the remaining reserves, an aggressive drilling and intervention programme is necessary. Future field development might also include a pressure blow down of the reservoir. So far the Statfjord Field has exhibited a fairly mild scale potential. Sulphate scale has been detected in several wells downhole; in the near well bore area, in the perforation tunnels or in the well bore. Well bore accumulation has been observed both as a thin layer along the tubing or as massive build up in the wire-line re-entry guide. Carbonate scale, when present, is mainly observed above the wireline retrievable downhole safety valve (DHSV). Statfjord wells are typically completed with wire-line retrievable downhole safety valves, which are function tested every 6 months. In wells prone to scaling this testing frequency is increased to 3-months. Seawater breakthrough in the Etive formation of Statfjord Well C-28 was first recorded during 1999. Following deterioration in well performance, scale dissolver and inhibitor squeezes were performed in 2000 and 2002. Production from the well was increased after these jobs, but scale build up in the 7" re-entry guide was confirmed during caliper logging in June 2003. A scale control program was initiated which included traditional scale inhibitor squeezes supported by scale dissolver treatments. Considerable emphasis was initially placed on identifying environmentally acceptable scale inhibitors that would provide cost effective scale control under Statfjord conditions to meet the business needs for green products. Much less emphasis has been placed on the development of environmentally acceptable barium sulphate scale dissolvers. Traditional sulphate scale dissolver formulations are generally based on DTPA and/or EDTA chemistry which are relatively effective at chelating barium and other divalent cation including strontium and calcium but do not display acceptable environmental profiles. These chemistries suffer with poor biodegradation and are thus placed on the substitution list under HCMS guidelines. This paper describes the development and laboratory evaluation of chelant chemistries of a scale dissolver with environmentally acceptable properties. It was compared in the field against traditional products when pumped into the same Statfjord well under "similar" conditions. The paper will highlight the identification of a particular molecular structure that gave superior barium and strontium sulphate scale dissolution rates and capacity in the laboratory as compared to traditional EDTA and DTPA based dissolvers whilst fully meeting the environmental requirements. Introduction The Statfjord Field was discovered in 1973, declared commercial in August 1974, and started production in 1979. The field is over 25 km long and averages 4 km in width, and is the largest producing oil field in Europe. Statfjord is located in the Tampen Spur area, in the northern portion of the Viking Graben and straddles the border between the Norwegian and UK sectors. The field is developed by three fully integrated Condeep concrete platforms. All three platforms have tie-ins, as shown in Figure 1. Production is from the Brent, Dunlin and Statfjord reservoirs, with the main reserves in the Brent and Statfjord reservoirs. At the end of December 2003 the cumulative oil production was 626.1 MSm3, giving a current recovery of approximately 63.2% of the STOOIP. The expected recovery factor at abandonment is 65.7%.
- Europe > United Kingdom > North Sea > Northern North Sea (1.00)
- Europe > Norway > North Sea > Northern North Sea (1.00)
- Europe > United Kingdom > North Sea > Northern North Sea > East Shetland Basin > Block 211/25 > Statfjord Field > Statfjord Group (0.99)
- Europe > United Kingdom > North Sea > Northern North Sea > East Shetland Basin > Block 211/25 > Statfjord Field > Cook Formation (0.99)
- Europe > United Kingdom > North Sea > Northern North Sea > East Shetland Basin > Block 211/25 > Statfjord Field > Brent Group (0.99)
- (21 more...)