Naphthenate Scale Formation – Examination of Molecular Controls in Idealised Systems

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe formation of calcium naphthenate precipitates and emulsions during oil production is becoming an increasing problem to the oil industry. Naphthenic acids, R-CO 2 H, are present in many crude oils and the hydrophilic nature of the carboxylic acid group means that they congregate at the oilwater interface. As the pressure drops during production and carbon dioxide is lost from solution, the pH of the brine increases, which in turn leads to dissociation of the naphthenic acid (RCO 2 H -> RCO 2 -). The naphthenates can then act as natural surfactants leading either to stabilised emulsions or solid deposits following complexation with calcium cations present in the aqueous phase. The naphthenate deposits collect predominantly in oil / water separators and de-salters but can also deposit in the tubing and pipelines.This study has looked at a variety of conditions to determine when certain carboxylic acids will form naphthenate deposits under idealised laboratory conditions. A range of naphthenic acids of different molecular structure were dissolved in an organic phase (toluene) and mixed with synthetic brines containing a range of calcium concentrations typical of oilfield production waters. These tests have determined that as the size of straight chain carboxylic acids increases so does the amount of naphthenate deposit. Increases in brine pH also increased the amount of deposit. However, the effects of changes in calcium concentration and molecular structure on the formation of naphthenate deposits were more difficult to quantify. The work assists in increasing our understanding of the factors controlling the precipitation of naphthenate solids under controlled conditions and forms the basis for future studies in real oilfield fluids.

Thermodynamic Modeling of Naphthenate Formation and Related pH Change Experiments

“…The development of acidic, sometimes biodegraded, crudes in different parts of the world may lead to naphthenate problems during oil production (Goldszal et al 2002;Laredo et al 2004;Havre et al 2003;Shepherd et al 2005;Ese and Kirkpatrick 2004;Vinstad et al 2003;Dyer et al 2003;Gallup et al 2002;Rousseau et al 2001;Havre 2002;Sorbie et al 2005). These naphthenate deposits have become an increasing flow assurance problem because of deposition and process disruption in production facilities (Goldszal et al 2002;Vinstad et al 2003;Gallup et al 2002;Rousseau et al 2001).…”

“…Naphthenic acids in hydrocarbons are defined as compounds containing carboxylic groups attached to saturated cyclic structures (Dyer et al 2003;Havre 2002;Sorbie et al 2005;Fan 1991;Gaiker and Maite 1996;Robbins 1998;Shepherd et al 2006;Mohammed et al, forthcoming). There is a tendency for the naphthenic acid to partition between the oil and water phases during production.…”

Detection and Removal of Naphthenate Deposit in Oil Well

“…The hydrophilic nature of carboxylic acid group in Napthenic acid (RCO 2 H) causes it to agglomerate at oil water interphase. Dissociation of napthenate acid (RCO 2 H -> RCO 2 ) happens when the pH of the formation water increases due to pressure drop in production and carbon dioxide lost from solution [2]. When the ion of the produce water (e.g.…”

Experimental Investigation and Modeling of Naphthenate Soap Precipitation Kinetics in Petroleum Reservoirs

“…Production of acidic crude may create various adverse problems during oil production [1][2][3][4][5][6][7] . Crude containing high concentration of naphthenic acid frequently leads to naphthenate soap precipitation by interacting with the ions present in the reservoir brine, and cause formation damage and well productivity loss in petroleum reservoirs.…”

“…Crude containing high concentration of naphthenic acid frequently leads to naphthenate soap precipitation by interacting with the ions present in the reservoir brine, and cause formation damage and well productivity loss in petroleum reservoirs. Naphthenate soaps create problems in various forms, including emulsification and scale formation [1][2][3][4][5][6][7] . Therefore, acquiring the knowledge about the mechanism, reaction kinetics, and rate equation of the naphthenate soap precipitation is of great importance for the petroleum industry to be able to control and/or minimize the loss of well productivity due to naphthenate soap precipitation in petroleum reservoirs.…”