Shubham, Agrawal (Texas A&M University at Qatar) | Martavaltzi, Christina (Texas A&M University at Qatar) | Dakik, Ahmad Rafic (Texas A&M University at Qatar) | Gupta, Anuj (Texas A&M University at Qatar)
It is well known that the majority of carbonate reservoirs are neutral to oil-wet. This leads to much lower oil recovery during waterflooding since there is no spontaneous imbibition of water in heterogeneous reservoir displacement. It has been verified by a number of researchers that Adjustment of ion concentration in brine solutions, or adding surfactant solutions can enhance the oil recovery by altering the wettability. In the published literature, contact angle studies usually refer to measurement on calcite crystals and there are no results for the contact angle of carbonate porous media representative of reservoir rocks. Moreover, there are few studies on the effect of non-ionic surfactants, compared to those for ionic surfactants. Understanding the effect of various ions and their concentration in the injection brine on the wettability of the Limestone outcrop core samples is the first step for tailoring of the optimum injection brine. This will be followed by a study of the effect of surfactant on the wettability of calcite crystal samples. The evaluation of the results may provide guidelines for the design of injection brines for efficient enhanced oil recovery from carbonate reservoirs.
In this work, a procedure is established for the measurement of the contact angle on limestone outcrop core samples. Results showed that, at atmospheric conditions, low salinity CaCl2 solution induced the most significant improvement on the wettability of the outcrop sample. Moreover, among all the non-ionic surfactants studied, only the presence of the two first members of the 15S analogous series might lead to a slight decrease of the contact angle.
Loktev, Andrey (Arctic Marine Engineering-Geological Expeditions) | Bondarev, Vladimir (Arctic Marine Engineering-Geological Expeditions) | Kulikov, Sergey (Arctic Marine Engineering-Geological Expeditions) | Rokos, Sergey (Arctic Marine Engineering-Geological Expeditions)
The estimation and prediction of wax formation and the understanding of the physicochemical characteristics of the wax phase are of major importance in flow assurance. The characterization of the oil and wax can provide useful estimates of the parameters and behavior required for operational engineering process developments and/or physical modifications to the processing of crude oils, aiming at the reduction of costs of production and transportation. The strategy employed in this study was to use temperature and fluid characterization analysis of Nigerian crude to predict the potential for paraffin wax related problems in Nigerian oilfields. This approach defined the oilfields with probably high risk of wax deposition potential amongst Nigerian crude. The synopsis of this paper proved that some Nigerian oilfield presents a potentially serious problem.
Tjioe, Martin (Department of Civil and Environmental Engineering, Stanford University) | Rahmani, Helia (Department of Civil and Environmental Engineering, Stanford University) | Borja, Ronaldo I. (Department of Civil and Environmental Engineering, Stanford University)
Organosilane has been explored previously as a kaolinite fixing agent, and surface modifier to enhance adsorption of scale inhibitors. Here, self-assembled organosilane films are investigated for their potential to prevent scale deposition directly, that is without the presence of scale inhibitors. Film formation on quartz crystals is analysed using a quartz crystal microbalance, which suggests that different film structures can be created using the same organosilane molecule. Brine tests using singlecrystal quartz coupons coated with organosilane indicate that calcium carbonate scale deposition can be reduced by 66%.
Keywords: adsorption, organosilane, inorganic scale precipitation, self-assembled monolayer, quartz
In order to assess scaling risk in pipes, a better understanding of scale deposition kinetics on steel surface under realistic and complex oil field condition is needed. In this paper, we introduce the development of a novel CaCO3 pre-coated steel tubing for studies of CaCO3 crystal growth kinetics and inhibition kinetics at oilfield conditions. This approach provides a relatively stable surface area and eliminates the limits of laboratory batch experiments. Initially, the heterogeneous precipitation rate of CaCO3 from a supersaturated solution (Calcite SI=0.3-0.7) was evaluated at specific temperatures (60-80???C), linear velocities (0.01-0.75 cm/sec), and ionic strengths (0.1-1M). The curve fitted heterogeneous precipitation rate constant, kppt, ranged from 10 -5 to10 -4 cm/sec. The results are comparable to that calculated from the Sieder and Tate equation, which indicates that the crystal growth was dominated by mass transfer rate. With the injection of scale inhibitors for one hour through the pre-coated tubing, the calcium carbonate precipitation can be prevented for days, and the crystal growth rate can be significantly slowed down. Not only does this study contribute to the limited data base of scaling kinetics in actual flowing pipes, but also provides a new approach to better understand the inhibitor reaction with the subsurface. The approach and results will assist in the prediction of scaling risk as a function of brine composition, well conditions and scale inhibitor composition, which will improve our ability to predict the severity of scale risk, including the rate of scaling, minimum blockage time, and thus the minimum inhibitory concentration needed in actual flowing pipes.
Sanders, Laura (University of Leeds) | Hu, Xinming (University of Leeds) | Mavredaki, Eleftheria (U. of Leeds) | Eroini, Violette (U. of Leeds) | Barker, Richard (University of Leeds) | Neville, Anne (U. of Leeds)
The formation of calcium carbonate scale and the occurrence of corrosion in CO2-saturated environments in different parts of oil and gas facilities are both phenomena that have been extensively studied. However, to date, very limited work has been carried out on evaluating combined products in a combined scale/corrosion methodology. This paper presents the results from a new combined bulk jar scaling/bubble cell corrosion test. The aim of this project is to investigate the effect of two combined chemicals in a new experimental setup; to study the corrosion and scale interactions which occur simultaneously. Two combined products were assessed at 5 ppm concentration at two temperatures (60ºC and 80ºC) in a CO2-saturated brine. Bulk scale precipitation was monitored using a turbidity meter and the corrosion rate measurements were made using the linear polarisation resistance (LPR) technique. Scale deposition and corrosion mechanisms have been studied using surface analyses. The performance of the two combined products has also been tested to measure: (i) the increase in the induction time of the calcium carbonate formation in the bulk, (ii) the change of the morphology of the crystals and (iii) the formation of a partial protective layer on the sample.
According to this study, the new experimental method has enabled the corrosion and scale deposition on pipeline steel (X65) and the bulk precipitation process to be studied simultaneously. Detailed scale deposition mechanisms on the material surface in the presence of corrosion processes and combined products are addressed from this study.
Keywords: calcium carbonate, scale, corrosion, combined inhibitors
Calcium carbonate and iron carbonate scales are widely observed in oil and gas production. Scale formation can be useful for corrosion control; however, excessive scale buildup can lead to severe production loss. What is called calcite scale in the field is almost always a solid solution of iron in calcite. Yet little attention has been paid to the precipitation of these mixed calcium-iron carbonate scales. As a result, knowledge of the formation and inhibition of mixed calcium/iron scales is very limited.
Normally, calcite scale formation is readily inhibited, whereas siderite inhibition is notoriously difficult. The solid-solution transition from predominantly calcite to predominantly siderite properties is unknown. Besides, although the solubility of mixed scale can differ by several orders of magnitudes from the solubility of its pure salts, scale prediction models are normally developed based on the data from pure solids. Finally, the incorporation of iron into calcite solid dramatically alters the kinetics of scale growth, as will be illustrated.
A series of experiments were performed to precipitate mixed iron-calcium carbonate (FexCa1-XCO3), ranging from calcium-rich to iron-rich. The experiments were conducted at 7.3±0.2 pH in 0.5 M NaCl at 55 oC. The work was performed with a new constant composition method, modified to handle oxygen sensitive ferrous carbonate scale and solid solutions.
Based upon the experimental results and a flux-based theoretical derivation, a new correlation in a form of a logistic function has been developed to predict the composition of FexCa1-xCO3 as a function of the aqueous composition. The model is an excellent representation for all of the experimental results, with R2 greater than 0.97. The correlation and methods developed in this work can readily be adapted to other mixed scale systems. Laboratory results will be compared with field observations and the consequences discussed.
Benvie, Ronald (Champion Technologies) | Chen, Tao (Champion Technologies) | Heath, Stephen Mark (Champion Technologies) | Chen, Ping (Champion Technologies Ltd.) | Montgomerie, Harry (Champion Technologies) | Hagen, Thomas Hille (Champion Technologies Ltd.)
Dynamic scale loop tests are one of the major test methods used in the oilfield scale industry to evaluate the minimum inhibitor concentration (MIC) performance of scale inhibitors under laminar flow conditions. However, this laminar flow condition may not often be representative of field flow conditions especially around chokes, downhole safety valves and in wells with ESP and ICD completions where the flow is turbulent. Under these turbulent flow conditions the MIC derived by standard dynamic loop test may be too low to inhibit scale formation and very seldom has focus been placed on the effect of turbulence on MIC of scale inhibitors.
It is possible to modify existing dynamic scale loop equipment to achieve turbulent flow conditions. However, the turbulent flow conditions imparted by the higher flow rate and narrow test coils still cannot match the really high Reynolds numbers experienced in real field conditions so a different approach was adopted to more closely replicate field conditions. This consisted of installing an adjustable small bore valve in the dynamic loop rig which closely simulates the turbulent environment around chokes and downhole safety valves.
This new methodology and testing under turbulent and laminar conditions (at lower Reynolds numbers) was used to gain an understanding of the impact of flow on scale deposition and MIC and this information was used to design and identify new environmentally friendly P containing scale squeeze inhibitors that demonstrated excellent performance under turbulent flow conditions.
This paper will give a comprehensive study of the effect of flow condition on the scale formation and inhibition and, in addition, will detail how this methodology and new chemistry can be coupled to a chemical technology toolbox, that also implements techniques for advanced scale inhibitor analysis and improved scale inhibitor retention, to design optimum scale squeeze packages for harsh scaling conditions.