Summary Calcium carbonate (CaCO3) scale is a common problem in the oil industry, leading to reduced well performance and obstruction of the safety valves. Recent field experiences indicate that scaling may be a problem at lowersaturation ratio (SR) than earlier anticipated. In a high-pressure, high-temperature scale cell, crystal growth in synthetic formation water has been studied. Induction times and growth rates have been determined by use of a microscope cell. The results have been interpreted by use of nucleation theory. The findings indicate that wells may be safely operated at SR below 2.5 at85°C. At higher temperature, crystal growth is less dependent on SR and the temperature dominates the system. Care should therefore be taken when operating wells at temperatures greater than 100°C. Introduction Precipitation and deposition of CaCO3 is a common problem in the oil industry. The scaling problems occur during pressure decrease of the produced formation water. The consequence may be reduced performance of the well and in some cases influence on the operation of downhole safety valves(DHSVs).The carbonates precipitate from the produced water as release ofCO2 gas gives increased pH and supersaturation of CaCO3 . The kinetics of the reaction is a function of temperature (i.e., slow kinetics at low temperature). The rule of thumb for prediction of CaCO3 scaling problems has until lately been based upon the work by Oddo and Tomson. Their conclusion from field experiences in the Hitchcock field in Texas, and Farida offshore Indonesia, was that produced water from vertical wells may be supersaturated up to saturation ratio SR=2.51 before any scaling problems occur. The bottomhole temperature was moderate (88 to 104 °C). In some relatively recent field developments, the design of the completion and the need for chemical placement in new wells(e.g., scale inhibitor injection lines) have been partly based on these findings.

Applied research has been undertaken to examine the potential of kaolinite combined with a kaolinite fixation agent to;Increase squeeze lifetime through alteration of near wellbore surface characteristics and mineralogy and,Provide water shut off control. With respect to enhancing squeeze lifetime, it is documented that kaolinite increases the quantity of inhibitor adsorbed. Conversely, clean sandstone with low clay content commonly provides a poor substrate for adsorption. Furthermore, in reservoirs that experience near wellbore formation damage due to kaolinite mobilisation, it has been shown that use of a fixation agent as part of a squeeze treatment can increase squeeze lifetime. Using these facts, research has assessed the feasibility of injecting microcrystalline kaolinite (average particle size 2 µm) combined with the fixation agent and scale inhibitor as a means of mechanically altering near wellbore mineralogy and surface property characteristics within clean, high permeability sandstones. The testing has been designed to mimic the squeeze procedure used in the field for performing such a job and involves no additional steps to that used in a normal squeeze, i.e. Pre-Flush ? Main Treatment ? Over-Flush. The paper presents the results of coreflood experiments that have been undertaken to demonstrate "proof of concept" for the above along with examples of potential field applications. A further concept, born from the initial idea, was the use of kaolinite and fixation agent for efficient, low cost, environmentally friendly water shutoff. There are several available products for water shutoff but the disadvantage of these is that they are not acceptable for use in Norway due to poor environmental characteristics. Hence, there was a need to fill this gap by developing water shutoff technology to meet country specific environmental legislation. The paper provides details of coreflood testing, where an excess of kaolinite has been used to form an internal and external filter cake that is attached to the wellbore face and within the near wellbore using the fixation agent. The paper draws on data from StatoilHydro operated fields in order to highlight the potential of this innovative approach to downhole scale management and water control.

Total 011 Marine; Kari Ramstad, Norsk Hydro as.; and Paul Griffin, Enterprise Oil q SPE Members -W9ht IWS. SocMY of Petmbum Engin@rs, Inc. This paper was pmpamd for presentation at the SPE Intwnathnal Sym~um on Oilfield CMW w in an A~Onb, TX, u. S.A -14-17 *~V 1* This paper was aekcted lor prawntattcm by an SPE Program committee Wowing review 01 information c+mtairmd in an 8Mmct submltbd by ttw authuts). COntenta of the P9PW, * -d. haw nor hen rfMewd by the SocretY of Petroleum Er@near'a M we subw to cmectmn bythOaurhOrts). ThOmatOM, as Prwem@, do-m~* wry poaitbn of the SaciMY of Petrotoum Engirwwa, w offiim, or members. P8PWS pmnnbd at SPE rnostings am wbjwt to publicdon reviw by Edhorial CommHton9 ot ttw Society d~m EW-. mxnmqbtiMd tomti-titi me~=-.ll~rMymtbOwPiBd. ThOabmmcttic=-n -=F@-=kõ r Mere and by wlwn the paper is rxwenbd. Write Ubrwian, SPE. P.O. Sox 8SSSSS, FMwOaOm TX 7SCWH4M, u.S.A. hbX, 1SS24S SPEUT. ABSTRACTIn this paper, results from static tests have been used to establish scale inhibitor adsorption mechanisms and levels in ... ...Lconsolidated reservoir cores and to ratm mmcmors for their adsorption behaviour and, in some cases, squeeze return lifetimes. The purpose of this rapid and simple type of bulk adsorption measurement is to assist in the selection of inhibitors for further coretlooding which should be carried out on a minimum number of inhibitors.A bulk adsorption sensitivity study can be canied out very rapidly compared with aref~]!v carried out reservoir condition core floods. The , ---------. . . value of such rapid screening tests is evident although we show that it is not always possible for all factors concerning squeeze lifetime to be determined in this way. It is still often necessary to carry out a much smaller number of reservoir condition core floods for a few (usually between 1 and 3) selected inhibitor products. This is necessary if the dynamic adsorption isotherm, I'(C), is to be derived in order to develop the "Field Squeeze Strategy" or for the assessment of formation damage which might occur in the squeeze treatment. A field example of this is presented briefly in this paper aithough cietaik can "Mfound eiseiviiere.

The sub sea development of the Ormen Lange gas field located in the Norwegian Sea will use MEG (mono-ethylene-glycol) for hydrate inhibition. Gas, condensate and MEG + water will be transported through a multiphase carbon steel pipeline to the onshore process plant at Nyhamna located on the west coast of Norway. pH adjustment and film forming corrosion inhibitor will be used to control the corrosion rate in the pipeline. Although the corrosion rate is low during production, iron will be produced due to corrosion and follow the MEG/water phase. Most of the iron will be removed as iron carbonate particles during the MEG regeneration process but about 10ppm iron as particles and ions is expected to circulate in the MEG-loop. Production of formation water will result in carbonate scaling when pH stabilised MEG is used as corrosion control unless a scale inhibitor is used. Three commercial scale inhibitors have been tested for this system. Tests have been performed without iron, with iron ions and with iron carbonate particles present. The results from the tests showed that the scale inhibitor concentration had to be increased considerably when iron ions were present compared to experiments without iron. The scale inhibitors performed poorer at the same inhibitor concentration in tests where iron carbonate particles were present than in tests with iron ions. Scale inhibitor concentrations up to 400ppm were used in the tests without achieving satisfactory scale protection when iron particles were present. In addition tests with lowering the amount of pH stabiliser have been performed. Tests with combining scale and corrosion inhibitors have also been performed. No scale inhibitors have shown satisfactory performance when iron carbonate particles were present in the tests. Introduction The Ormen Lange gas field is a sub sea development located in the Norwegian Sea 120 km from the shore in mid Norway. Norsk Hydro Produksjon is operator for the planning and development phase. Shell will take over as operator when Ormen Lange comes on-stream in October 2007. Sub-zero seabed temperatures in combination with the high-pressure conditions in the carbon steel multi phase pipelines favour the formation of gas hydrates and ice. MEG (mono-ethylene-glycol) will be injected to prevent hydrates and ice from forming in the sub sea pipeline. The MEG will be pumped out to the injection point in carbon steel pipelines. From the start of production the wells will also produce condensed water (CW), CO2 and organic acids, besides hydrocarbons. The pH of this water phase will be low due to the presence of CO2 and organic acids. pH adjustment and film forming corrosion inhibitor (CI) will be used to control the corrosion rate in the carbon steel pipeline1. The pH stabiliser will be added to the MEG. The degree of pH adjustment varies from full pH stabilisation to partial pH stabilisation. When partial pH stabilisation is used, a film forming corrosion inhibitor has to be used in combination with pH stabilisation to achieve corrosion control in the pipeline. Although the corrosion rate is low during production, iron will be produced due to corrosion and follow the MEG/water phase. Most of the iron will be removed as iron carbonate particles during the MEG regeneration process but about 10ppm iron as particles and ions is expected to circulate in the MEG-loop. Later in the field life formation water (FW) breakthrough may occur in the wells resulting in a co-production of FW and CW. CaCO3 crystals may form if the formation water mixes with the pH-stabilised MEG. The high pH and the presence of MEG reduce the solubility of CaCO32. The crystals may form a layer on the pipeline wall. The MEG that is pumped out from the onshore facilities is denoted Lean MEG, while Rich MEG is the Lean MEG after this has been mixed with the well fluids. Several commercial scale inhibitors (SI) have been tested in dynamic tube blocking tests and static tests. Since iron is known to have influence on the performance of scale inhibitors3 their efficiency was determined with and without the presence of iron.

Total 011 Marine; Kari Ramstad, Norsk Hydro as.; and Paul Griffin, Enterprise Oil q SPE Members -W9ht IWS. SocMY of Petmbum Engin@rs, Inc. This paper was pmpamd for presentation at the SPE Intwnathnal Sym~um on Oilfield CMW w in an A~Onb, TX, u. S.A -14-17 *~V 1* This paper was aekcted lor prawntattcm by an SPE Program committee Wowing review 01 information c+mtairmd in an 8Mmct submltbd by ttw authuts). COntenta of the P9PW, * -d. haw nor hen rfMewd by the SocretY of Petroleum Er@near'a M we subw to cmectmn bythOaurhOrts). ThOmatOM, as Prwem@, do-m~* wry poaitbn of the SaciMY of Petrotoum Engirwwa, w offiim, or members. P8PWS pmnnbd at SPE rnostings am wbjwt to publicdon reviw by Edhorial CommHton9 ot ttw Society d~m EW-. mxnmqbtiMd tomti-titi me~=-.ll~rMymtbOwPiBd. ThOabmmcttic=-n -=F@-=kõ r Mere and by wlwn the paper is rxwenbd. Write Ubrwian, SPE. P.O. Sox 8SSSSS, FMwOaOm TX 7SCWH4M, u.S.A. hbX, 1SS24S SPEUT. ABSTRACTIn this paper, results from static tests have been used to establish scale inhibitor adsorption mechanisms and levels in ... ...Lconsolidated reservoir cores and to ratm mmcmors for their adsorption behaviour and, in some cases, squeeze return lifetimes. The purpose of this rapid and simple type of bulk adsorption measurement is to assist in the selection of inhibitors for further coretlooding which should be carried out on a minimum number of inhibitors.A bulk adsorption sensitivity study can be canied out very rapidly compared with aref~]!v carried out reservoir condition core floods. The , ---------. . . value of such rapid screening tests is evident although we show that it is not always possible for all factors concerning squeeze lifetime to be determined in this way. It is still often necessary to carry out a much smaller number of reservoir condition core floods for a few (usually between 1 and 3) selected inhibitor products. This is necessary if the dynamic adsorption isotherm, I'(C), is to be derived in order to develop the "Field Squeeze Strategy" or for the assessment of formation damage which might occur in the squeeze treatment. A field example of this is presented briefly in this paper aithough cietaik can "Mfound eiseiviiere.