SPE Abstract. Introduction

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1 SPE Downhole Scale Control on Heidrun Field Using Scale Inhibitor Impregnated Gravel Olav Martin Selle, Frode Haavind, Marit H. Haukland and Arild Moen, Statoil; Carl F. Hals and Kåre Øien, Schlumberger; Catherine Strachan and Graham Clark, Clariant Oil Services Copyright 21, Society of Petroleum Engineers This paper was prepared for presentation at the SPE International Conference on Oilfield Scale held in Aberdeen, United Kingdom, May 21. This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 3 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright. Abstract Scale inhibitor impregnated gravel (SIIG) is a new technology for combined sand and scale control that features porous ceramic proppant particles that are impregnated with scale inhibitor chemistry. The particles have been designed to be suitable for gravel pack pumping operations and can be pumped as 1% scale inhibitor impregnated particles or mixed with conventional gravel. The scale inhibitor impregnation technology has been optimised to provide a steady, controlled release of scale inhibitor chemical on contact with produced water. The technology provides for the first time in the oil industry a method of placing large quantities of solid state scale inhibitor in gravel packs. In typical gravel packed deepwater completions, particularly, sub-sea wells, the technology offers considerable cost benefits for scale control when compared to scale inhibitor squeeze treatments and negates the need for pre-emptive squeeze treatments in anticipation of seawater breakthrough. After qualification of the product through a comprehensive laboratory development programme a field trial has been performed on a Heidrun well. The well was a sidetrack from the mother well, and it was chosen for the field trial as the initial water breakthrough was predicted to contain around 2% sea water. The field trial demonstrated that placement of the scale inhibitor impregnated particles could be successfully performed. However, the loss of scale inhibitor to the gravel pack fluid was higher than anticipated since it took three weeks between gravel packing and startup of the well. Despite the high intial loss of scale inhibitor to the gravel pack fluid the release of inhibitor during production was as planned. Unfortunately it did not protect the well from scaling since the mixing of sea water and formation water probably took place in the near well area behind the gravel pack. This paper will provide a detailed description of the laboratory development of SIIG technology and, in addition, will also present details of the first gravel pack deployment of this technology for combined sand/scale control in a Heidrun well. Introduction The deposition of inorganic scale during the production of hydrocarbons is a major problem. The primary effect is deferment of oil production due to scale deposition in the near well bore and tubing of production wells and in the propped hydraulic fractures, gravel and fracture packs. Scale problems are currently managed by the use of preventative and remedial chemical treatments that often involve significant costs to the operator, especially in advanced and deepwater wells (Wigg and Fielder, 1995, Schmidt, 1995, Thornton et al. 1997, Shuler and Jenkins, 1991). Previous papers have described the development of porous scale inhibitor impregnated proppants (SIIP) and highlighted the initial returns from field trials performed in onshore wells on the North Slope of Alaska (Bourne et al. 1995, Collins, 1997, Webb et al. 1997) and in offshore North Sea wells (Norris et al. 21). However, the SIIP was not considered to be applicable to gravel pack application because the the maximum concentration of scale inhibitor that could be incorporated into the solid matrix was approximately 12 wt%/v. This scale inhibitor content was

2 2 SPE considered too low to provide a reasonable scale control lifetimes in this type of well completion. The SIIP technology has therefore been further developed into SIIG technology (scale inhibitor impregnated gravel) with a much higher scale inhibitor content to produce a stable product suitable for deployment in gravel packs. One SIIG treatment has recently been deployed on a Heidrun well. The treatment was designed to protect the gravel pack and sand screen against scaling during sea water breakthrough. The well is a deviated oil producer in the Garn and Ile formations at Heidrun. It is completed with an openhole gravel pack, 5 ½ wire wrapped screens in a 7 hole and has gas lift. The completion diagram for the well is presented in Figure 1. The formations are of good quality; Garn has a permeability of ~ 2 md, while Ile has a permeability of ~ 5 md. The porosity is in the range of 3 to 32 %. The expected sea water cut (percent of the total water production) was expected to be 2% on start up, and the well would require scale protection from the start of production. Only barium sulphate scale is an issue in this well as precipitation of calcium carbonate was not anticipated. Fig. 1 Heidrun well completion diagram. Screens are installed in Garn and Ile formations. The Heidrun Field and the effort to extend scale inhibitor squeeze life has been described earlier (Selle et al. 22). The field is located in the Haltenbanken area offshore Mid-Norway. Seawater injection is used on the field to increase recovery and for pressure support. With Ba 2+ levels ranging from 6 to 3 ppm, downhole scale control is a particular challenge. Background Gravel Packing Gravel packing is a commonly applied technique to control formation sand and fines production from oil and gas wells. A typical gravel pack completion is presented in Figure 2. In a gravel pack completion a screen is placed in the well across the productive interval. Specially sized, high permeability gravel pack sand is mixed in a carrier fluid and circulated into the well to fill the annular space between the screen and the formation. Any gap or interruption in the pack coverage will enable undesirable sand or fines to enter the producing system. The success of an openhole gravel pack is dependant upon the formation type, screen type, appropriate fluid loss control, formation stability, borehole geometry, the size and density of the gravel and the β wave placement pressure. The Heidrun asset has over the past decade developed gravel packing best practices/methodologies to overcome these challenges and to achieve good gravel placement.

3 SPE Fig. 2 Typical gravel pack completion Scale Control in Gravel Packs Sustaining the well productivity is dependent on preserving the high conductivity of the gravel pack. This is at risk when bottomhole conditions encourage the formation of mineral scales. Scale control in gravel packs in the Heidrun wells has been previously achieved by conventional bullhead squeeze treatments and remedial dissolver jobs (Wat et al. 21). However, the bullhead squeeze operation is a non-selective process that leads to uncertainties in the extent of coverage of water producing zones and therefore the full length of the gravel pack is often not protected. To address the issues of scale inhibitor placement in gravel packed wells, whilst also delivering long term treatments, SIIG technology has been developed for combined scale and sand control in such wells. SIIG is an improvement on SIIP technology, which was originally designed for use in hydraulic fracturing treatments. The SIIG technology features highly porous (up to 25%), high strength proppant particles that are impregnated with scale inhibitor chemistry. The particles have been designed to be suitable for gravel pack pumping operations, and can be pumped as 1% impregnated particles or mixed with conventional gravel. The technology was optimised for the downhole scaling conditions in this particular well. The scale inhibitor will remain dormant in the gravel pack until contact with water providing a steady, controlled release of chemical into the produced water. This concept is illustrated in Figure 3. The scale inhibitor will be preferably released at or above minimum inhibitor concentration (MIC) for as long as possible. This eliminates any waste of inhibitor when only oil or gas is produced, and potentially reduces the number of well interventions required by scale squeeze treatments. In addition, the SIIG technology does not rely on adsorption/desorption processes that are essential for the success of conventional squeeze treatments, and the concerns about effective scale inhibitor retention are minimised. The SIIG technology can also protect the whole of the gravel pack, and for squeeze treatments in long openhole completions this is usually only possible with mechanical or chemical diversion. However, the technology cannot protect the well outside the gravel pack.

4 4 SPE Fig. 3 Scale inhibitor release in gravel pack The development of the SIIG technology for the Heidrun Asset was not an easy task. A suitable product for field deployment could be defined as a scale inhibitor impregnated gravel that has sufficient strength to maintain gravel pack conductivity whilst being able to provide effective scale control during well production. Thus it was necessary to increase the scale inhibitor impregnation capacity of the gravel by increasing the internal porosity of the gravel whilst maintaining the strength of the product. This could not be achieved with standard light weight based gravels. It was therefore necessary to develop a high porosity, high strength proppant (HSP) based upon bauxite which could contain > 2wt%/v impregnated scale inhibitor and still pass the conductivity test for gravel pack application. The pack permeability data for 2/4 mesh HSP SIIG is presented in Figure 4. Fig. 4 SIIG gravel pack permeability data for 2/4 mesh HSP The proppant size and type and the scale inhibitor to be impregnated were all selected by industry standard techniques to match Heidrun requirements. In addition, the impregnated scale inhibitor solution has been formulated to improve its compatibility with the gravel pack fluid.

5 SPE Scale Inhibitor Evaluation The scale inhibitor identified for impregnation was selected to meet the Norwegian environemtal requirements and to provide adequate scale protection under Heidrun downhole conditions with 2% seawater breakthrough. A polymeric based scale inhibitor was identified for evaluation. The performance of the selected scale inhibitor was evaluated using conventional dynamic scale loop tests that are used for screening scale inhibitors for downhole squeeze or continuous injection applications (Oilfield Scale Research Group, 1995). The Heidrun brine chemistry used for the MIC evaluation for Ile formation is detailed in Table 1 below. Table 1 Heidrun Ile formation water composition Concentration / mg/l Ion Species Heidrun FW Seawater Na K Ca Mg Ba Cl - 33, HCO SO The performance data for the selected scale inhibitor is presented in Figure 5. The data indicated that the minimum inhibitor concentration (MIC) required for effective scale control under 9/1 ratio formation water/sea water (FW: SW) conditions was 2 ppm. Additional tests with formation water from Heidrun Tilje formation (Ba = 265 ppm) gave under 7/3 FW: SW conditions a MIC of 5 ppm. The anticipated MIC for the well with 2 % seawater would be between 5 1 ppm Blank SIGG Scale Inhibitor Differential Pressure (psi) ppm 8 ppm 6 ppm 4 ppm 2 ppm ppm Time (secs) Fig. 5 Dynamic Scale Inhibition Performance of SIIG Scale Inhibitor SIIG Manufacture The SIIG was produced using a vacuum impregnation and a rotary drying technique. The impregnation fluid contained the required active scale inhibitor and a number of other components designed to improve compatibility with the gravel pack fluid and to allow the production of a final product with very low moisture content (<.2%) and low fines content. This low moisture content was necessary for long term product storage and application in humid environments.

6 6 SPE The features of the SIIG are presented in Figure 6. Quality assurance (QA) of the manufacturing (impregnation) process and quality assurance (QC) of the SIIG was also seen as critical aspect of the pre-job preparation, and inspections and controls during the manufacturing were conducted. A final QA/QC lab testing was conducted upon receipt of the field batch of the SIIG. Samples of the SIIG were taken at various points during the manufacturing process and their physical appearance and fines production potential was examined using a specially designed turbidity technique and Scanning Electron Microscopy (SEM) respectively. In addition, the impregnated scale inhibitor content was measured to make sure it met the required specifications. The general appearance of SIIG under a light microscope is depicted in Figure 6. This highlights the regular rounded nature of SIIG. A detailed SEM image of a cross-section of one SIIG bead also demonstrates the porous nature of the material. Fig. 6 Features of 2/4 mesh HSP SIIG Static Fluid Compatibility Tests Static experiments were performed to evaluate the compatility of the SIIG with the various fluids encountered during the gravel pack process and to examine the scale inhibitor dissolution kinetics at low temperatures (1 C and 2 C) while gravel packing, and at Heidrun downhole temperature (85 C) during shut in. The static jar tests were performed in Heidrun formation water, 1.2 SG (specific gravity) NaCl, and 1.2 SG CaCl 2. The gravel pack fluid normally used at Heidrun is 1.2 SG NaCl. The scale inhibitor analysis for these tests was performed by dialysis/hplc. The uncertainty in the analysis in the range of 5 25 ppm scale inhibitor is ±1%, and more than 1% if the concentration is above 25 ppm. The uncertainty is greater for higher concentrations because the samples need to be diluted. No direct compatibility problems were encountered and the scale inhibitor dissolution kinetics from the SIIG indicated that <2% of the impregnated scale inhibitor was released into a static gravel pack fluid of 1.2 SG NaCl after 24 hours at 85 o C, see Figure 7. This amount was significantly decreased at the lower temperatures in both 1.2 SG NaCl and 1.2 SG CaCl 2 which would be expected from this type of product in a field depolyment. After test periods of up 6 hours more than 3% of the impregnated scale inhibitor was released in 1.2 SG NaCl. For 1.2 SG CaCl 2 the release is less, see Figure 8. Here the temperature was ramped up from room temperature to reservoir temperature to mimic the temperature profile for the gravel pack fluid during gravel packing. Typical time for completing a new well at Heidrun is 12 days (288 hours); that is from when the gravel pack operation start-up until the upper completion is installed and the well is ready for production. If operational problems occur, this time period may be much longer.

7 SPE #gram Inhibitor dissolved/total #gram active Inhibitor Time (hours) Formation water at 85C 1.2 SG NaCl at 85C 1.2 SG NaCl at 2C 1.2 SG NaCl at 1C Fig. 7 Static scale inhibitor dissolution kinetics of SIIG in Heidrun formation water and 1.2 SG NaCl at different temperatures #gram Inhibitor dissolved/total #gram active Inhibitor SG CaCl2 at 27-85C 1.2 SG NaCl at 27-85C Time (hours) Fig. 8 Dissolution kinetics of SIIG in 1.2 SG NaCl and 1.2 CaCl 2 at temperature ramping from 27 to 85 C Dynamic Release Tests Dynamic release tests were performed to provide information on the effects of fluid velocity on scale inhibitor release from the SIIG under simulated field conditions. The tests were performed in a specially designed cell at the typical field flow rates encountered in a gravel packed well. Two sand packs were made by packing 1% SIIG and two were made by packing 5% SIIG and 5 vol% standard light weights 2/4 gravel. The tests were conducted at residual oil saturation, and stock tank crude from Heidrun A-22 was used for sandpack saturation purposes. In the experiments with 1% SIIG grams of the inhibitor were used, i.e grams active impregnated scale inhibitor, and for the tests with 5% SIIG and 5% 2/4 standard light weight gravel 25.9 grams of active impregnated inhibitor were used. The sand packs were mounted vertically during saturation. The sand packs were evacuated and formation water was pumped in at 85 C. Initial water saturation (S wi ) was established by injecting stock tank oil from the top of the sand pack at back pressure of 1 bars. The initial rate was.5 ml/min until breakthrough of oil. The rate was then raised to 5 ml/min and finally 1 ml/min. Residual oil saturation by water flooding (S orw) was obtained by injecting formation water from the bottom of the sand pack. Data for the different sand packs are given in Table 2 below.

8 8 SPE Table 2 Sand pack data for dynamic scale inhibitor release rate tests Sand pack Length (cm) Diameter (cm) PV (ml) S orw (%) K w at S orw (md) 1% SIIG % SIIG % SIIG + 5% standard light weight 2/ % SIIG + 5% standard light weight 2/ Typical well rates anticipated for the well were converted to laboratory rates in the specially designed flow cell. Two different rates were applied, 2 and 15 ml/min. This corresponded to a water production of 27 and 22 m 3 /day respectively. Effluent samples were taken continuously from 1 to 1 PV, then at intervals up to 5 PV and analysed for scale inhibitor content by dialysis/hplc. The results from the dynamic release rate experiments are given in Figure 9. The SIIG inhibitor return profiles are very favourable indicating that the SIIG could provide adequate scale control at 2% seawater breakthrough conditions. The initial wash out of the impregnated scale inhibitor was very low, leaving the majority of the deployed inhibitor within the SIIG and thus available to inhibit against formation of scale in the gravel packs. However, these experiments did not take into account the 12 days soaking period from the start of the gravel packing process until the well is finished and ready for production. Concentration (ppm) % SIIG 15 ml/min 5% SIIG 15 ml/min 1% SIIG 2 ml/min 5% SIIG 2 ml/min PV Fig. 9 SIIG scale inhibitor return profile at 2 and 15 ml/min The mass balance data for the dynamic release tests was calculated and is presented in Table 3. As shown here lager quantities of scale inhibitor was detected than was actually present in the sand pack. The difference is probably due to some uncertainty with the scale inhibitor analysis. However, the data indicates that for both the high and low rates with 1% SIIG it seems that all of the the active scale inhibitor is released during the flooding with produced water. However, for the tests with 5% SIIG at both the high and low rate only about 1/5 of the active scale inhibitor was released. This has been seen in previous experiments as well, but we have no good explanation to why this is happening. The data also indicates that the scale inhibitor release rate from SIIG is not rate dependent.

9 SPE Table 3 Calculated mass balance for SIIG Dynamic Release Rate Tests Total active scale inhibitor in the sand pack (gram) 1% SIIG and 15 ml/min % SIIG and 2 ml/min % SIIG and 15 ml/min % SIIG and 2 ml/min Total active scale inhibitor dissolved (gram) Gravel Pack Placement Test The introduction of high density SIIG represented a change in gravel pack pumping design parameters for Heidrun, as seen in Table 4. It was therefore necessary to ensure that introduction of this new technology did not jeapordize the placement aspects of the treatment. This initiated a gravel pack placement qualification project. The project involved a yard test gravel pack pumping job using a large-scale well model where all dimensions (ID/OD) were real size besides the length. Samples of representative fluid and gravel were used during the experiment in order to, as closesly as possible, mimic real job conditions. The purpose of the experiment was to study the alpha and beta wave behaviour and to identify the degree of risk of having a premature screen-out. The test was successful as the pressure during the test was below critical limits and the sand pack efficiency was over 1 % of defined annulus capacity. A summary of the test data is found in Table 5. Table 4 Specification of gravel pack material SIIG Standard gravel Mesh Size 2/4 2/4 Gravel Bulk Density 1,68 1,64 Gravel Pack- Packing volume fraction,59,59 Gravel specific gravity 2,8 2,71 Proppant Grain Porosity,23 - Gravel Concentration 33.1 kg/m3 brine kg/m3 brine Table 5 Data from onshore testing in large-scale well model Washpipe OD: 4 inch Gravel bulk density: 1.68 g/cc Screen baspipe OD: 5.5 inch Slurry pumped: 29 m3 Wire wrap OD: 6.6 inch Gravel Placed 518 litre Swell Packer OD: 8.25 inch* Theoretical capacity of annlus: 463 litre Packer Base Pipe OD:7 inch (Top screen to bottom screen) OH ID: 8.5 inch Total pack efficiency: 1+ % Gravel conc.: 3 kg/m3 Carrier fluid: 1.2 SG NaCl Slurry rate: 11 lpm Proppant type: 2/4 porous scale inhibited

10 1 SPE Field implementation results The gravel pack operation in the well went very well. A total of 725 m3 slurry with 33 kg/m3 gravel concentration was pumped at a rate of 11 lpm. Pumping time was approx hours. The volume of gravel used was m3 which corresponds to a pack efficiency of 96.6 %. The alpha wave packing was 54 % and the beta wave 46 %. The returning gravel pack fluid was sampled for scale inhibitor analysis, and the results are presented in Table 6. The brine slurry samples indicated that high levels of scale inhibitor were initially released in the gravel pack fluid. However, this was expected after a well shut in period of 3 weeks. Table 6 Scale inhibitor concentrations of samples taken during gravel packing Scale inhibitor (ppm) Brine Sample Brine Sample SIIG/Brine Slurry Mix 1 27 SIIG/Brine Slurry Mix SIIG/Brine Slurry Mix The SIIG scale inhibitor return profile from the gravel pack during start up and production of the well show that even though higher levels of scale inhibitor than anticipated were initially released, the SIIG still worked as planned; see Figure 1. Res. SI w ater (ppm) % SI left in proppant 1 12 [Scale Inhibitor] mg/l % Scale Inhibitor left in proppant Produced water/m3 Fig. 1 SIIG Scale Inhibtor Return Profile from the Heidrun well However, the liquid productivity index (PI) in the well dropped significantly after production start up, see Figure 11. Most likely did the well experience formation damage due to the precipitation of scale since the Ba concentration fell from 74 ppm to zero within hours as plotted in Figure 12.

11 SPE PI [Sm3/D/bar] Fig. 11 Productivity Index (PI) of the well after SIIG gravel pack job The water cut of the well leveled out at around 27% after start up and the ion data indicated that the the sea water cut from sulphate concentration initially was started out at zero then increased rapidly to around 55%, see Figure ppm barium Sea water cut apr 13.apr 18.apr 23.apr 28.apr 3.mai Fig. 12 Barium concentration and sea water cut during start up of the well Since the scaling appeared to happen behind the gravel pack the impregnated gravel was not able to handle that scaling scenario. The water composition was determined by IC (Ion Cromatograph) and an analysis of the measured Ba ion data compared to what it should be if dilution had just occurred is presented in Figure 13. Clearly, the measured Ba values are below the sea water cut dilution line and deposition of BaSO 4 (s) was occurring.

12 12 SPE SW cut dilution line Measured values SW cut [%] Ba cons. [mg/l] Fig. 13 Sea water cut dilution line for barium concentration in the well Even if the scale inhibitor released from the impregnated gravel was above MIC (Figure 1), scaleing occurred and the well lost productivity. It was therefore decided to close the well waiting for a scale inhibitor squeeze job, and later a scale dissolver job. The squeeze job was able to protect the well as the Ba concentration increased from zero to 39 ppm, see Figure 12. This shows that the scaling occurred behind the gravel pack where the scale inhibitor released from SIIG was unable to protect. Conclusions Scale Inhibtor Impregnated Proppant has been further developed to enable effective deployment in gravel packs. Gravel packing with scale inhibitor impregnated gravel is now a proven method from an operational aspect, and can be planned for on future Heidrun wells. Scale inhibitor impregnated gravel is in general qualified for use at Heidrun field for wells with initial sea water breakthrough. However, several limitations in using scale inhibitor impregnated gravel technology have been revealed: Suited for wells with medium to low scale potential. Suited for wells where scaling occurs in the gravel pack, sand screen or the tubing % of the scale inhibitor content might be lost while completing the well. Mixing scale inhibitor impregnated gravel and ordinary gravel 5/5 might release only 2 % of the total amount of scale inhibitor, while unmixed scale inhibitor impregnated gravel releases all. The residual scale inhibitor concentration was difficult to detect, which may have given some uncertainty in mass balance calculations Future work Further development of SIIG is currently ongoing to improve on the scale inhibitor chemistry to reduce the intial release to completion fluids and to provide more effective scale protection under moderate barium sulphate scaling conditions at higher seawater breakthough. The use of non aqueous deployment fluids will also be considered. Acknowledgments The authors would like to thank the management of Schlumberger, Clariant Oil Services and Statoil and their partners in the Heidrun asset (Petoro, ConocoPhillips Skandinavia, and Eni Norge) for permission to publish this paper. The results and opinions presented in this paper do not necessarily reflect the view of the Heidrun partnership. The authors would also like to thank Karin Stene, Statoil and Harald Førdedal, former Statoil, for their valuable contribution during planning of the well and SPE for accepting this paper for publication. Nomenclature FW = formation water HSP = high strength proppant IC = ion chomatography MD = measured depth MIC = minimum inhibitor concentration QA = quality assurance

13 SPE QC = quality control SG = specific gravity SIIG = scale inhibitor impregnated gravel SIIP = scale inhibitor impregnated proppant SEM = scanning electron microscope Reference List Bourne, H.M., Knapstad, B., Nistad, T., Neigart, B., Ravenscroft, P., Read, P., 1995, "A Novel Scale Inhibitor Delivery System for Horizontal and Problem Wells". Paper presented at IBC Scale Conference. Collins, I.R., 1997, " Scale Inhibitor Impregnated Particles - Field Applications" Paper presented at IBC Scale Conference. Norris, M., Perez, D., Bourne, H.M., Heath, S.M., 21, Maintaining Fracture Performance through Active Scale Control Paper SPE 683 presented at the 3 rd International Symposium on Oilfield Scale, Aberdeen, UK. Oilfield Scale Research Group, 1995, "Experimental Procedures Manual Version 2." Department of Petroleum Engineering, Heriott Watt University, Edinburgh, UK. Schmidt, T., 1995, "Experience with Controlling Scale in Gravel Packs" Paper presented at IBC Scale Conference. Selle, O.M., Wat, R.M.S., Vikane, O., Nasvik, H., Chen, P., Hagen, T., Montgomerie, H., Bourne, H., 23, A Way Beyond Scale Inhibitors Extending Scale Inhibitor Squeeze Life Through Bridging Paper SPE 8377 presented at SPE Oilfield Scale symposium, Aberdeen, UK. Shuler, P.J., Jenkins, W.H., 1991, "Prevention of Downhole Scale Deposition in the Ninian Field" SPE Production Engineering, May. Thornton, A.R., Bourne, H.M., Ntombo-Tsibah, H., Taylor, K., 1997, "First Experience of Squeezing a Multi-Lateral, Horizontal Well in the Tern Field" Paper presented at IBC Scale Conference. Webb, P., Nistad, T., Knapstad, B., Ravenscroft, P., Collins, I.R., 1998, "Economic and Technical Advantages of a Revolutionary Chemcial Delivery System for Fractured and Gravel Packed Wells: comparative Analysis of Onshore and Offshore Subsea Applications" Paper SPE presented at SPE International Symposium on Formation Damage Control, Lafayette, Lousiana, USA. Wat, R., Selle, O.M., Børstad, H., Vikane, O., Hagen, T., Chen, P., MacLean, A., 21, Scale Inhibitor Squeeze Treatment Strategy on Heidrun Paper SPE presented at SPE European Formation Damage Conference, The Hauge, The Netherlands. Wigg, H., Fielder, M., 1995, "Establishing the True Cost of Downhole Scale Control" Paper presented at IBC Scale Conference. Appendix 1 Static jar test procedure for 85 C 1 ml of the Heidrun well formation water was placed in an oven at 85 C for 2 hours 5. grams (1.15 g active inhibitor) of SIIG particles was transferred to a glass tube (5 ml) and placed in an oven at 85 C for 2 hours The tubes were placed inside a separator bottle With the aid of a pipette, 5. ml of heated formation water was transferred to each of the tubes containing 5. g of the SIIG particles The separator bottles were sealed with a heat resistant cap and placed in the oven. 5 ml samples were extracted with a 5 ml syringe equipped with a.9 x 7 mm needle and a 1.2 µm disc filter after.5, 2, 6, 12, 24 hours. One bottle, containing 5. grams SSI and 5 ml HFW, for one time step was used i.e. a total of five bottles. The static jar tests at 2 and 1 C were performed by use of a water bath.

14 14 SPE The long term static jar tests were performed by use of a water bath. 2.5 grams of SIIG particles was transferred to a glass tube (5 ml) and placed in the water bath at 27 C With the aid of a pipette, 25. ml of heated 1.2 SG NaCl and 1.2 SG CaCl 2 was transferred to each of the tubes containing 2.5 g of the SIIG particles 25 ml samples were extracted with a syringe equipped with a.9 x 7 mm needle and a 1.2 µm disc filter Mixing and packing procedure of the dynamic flooding experiments SIIG particles and standard light weight 2/4 gravel were mixed and packed in the following way: 1. Equal amount of SIIP particles and 2/4 standard light weight gravel were transferred to a 1-litre glass bottle. 2. The bottle was sealed and turned upside down 4 times to homogenise the mixture. 3. The mixture was transferred to a rubber sleeve in batches of approximately 5 ml. 4. During transfer the sleeve was slanted from the vertical by approximately 2. Between transfers of each batch of mixture the holder was raised to vertical position and the mixture deposited in the sleeve compacted by hand using a large Teflon dowel.