The formation of inorganic, sparingly soluble salts from aqueous brines during oil and gas production, is known as ‘scale’ and is one of the major flow assurance problems. Scale forms and deposits under supersaturated conditions, wherever the mixing of the incompatible types of water; formation water from the bottom hole and the injected seawater, takes place. The deposited scale adheres on the surfaces of the producing well tubing and on parts of water handling equipment, where it builds up in time and leads to problems in reservoirs, pumps, valves and topside facilities. Since the deposition/adhesion takes place also in heat transfer equipment such as boilers and heat exchangers, a decrease in the performance during the heat exchange as well as in flow rates occurs. These problematic conditions are found not only in the oil fields but also in the distillation plants. The rapid increase of the mineral deposits leads to inevitable damage of the equipment parts. As a consequence, suspension of oil operations is necessary for the recovery or replacement of damaged parts. In the oil field these interruptions are accompanied by extremely high costs.
Current and future research
The two common, most insoluble types of inorganic scale formed during the extraction of the oil, are calcium carbonate (CaCO3) and barium sulphate (BaSO4). Both types of mineral scale are widely known from the different applications in daily life. However when it comes to the oil field processes, both mineral types like others (i.e. CaSO4, FeCO3) are undesirable since they result in blockage of pipes and in many other flow assurance problems. A number of past and on-going projects of this research group focuses on the CaCO3 and BaSO4 formation processes that occur in the bulk phase and on the surfaces. Furthermore the scaling activity is investigated in terms of both thermodynamics and kinetics.
High importance is given in with the performance of different chemical retarders (inhibitors) on the forming scale. The applied inhibitors are characterized by different chemical properties and they belong in different levels concerning their “green” character. In addition, the application of combined products with a double action on the scale and corrosion phenomena consists an interesting and further ambitious approach in the oil field. The first attempt from using combined inhibitors has shown that scale and corrosion phenomena can be both inhibited simultaneously.
Besides the processes that take place in the topside facilities, recently the scale formation processes occurring at the bottom hole were also given attention. The induction of the nanotechnology in the research and development of the anti-scaling techniques in the oilfield, offers the ability to understand and accurately simulate the bottom hole scaling activity. Current, related research projects include: Nanotechnology for Enhanced Squeeze Retention and Coating of the Wellbore Grain Surface to Prevent Scale Deposition/Adhesion, respectively.
In addition to their high industry relevance and impact, 'scale formation' studies are academically attractive since they are closely related to the dominant topics of (i) nucleation and (ii) crystallization of inorganic material. This is why the assessment of the actual mechanisms of the scale formation processes is such a prominent and active focus of this research group. A deeper investigation of the scale and formation damage phenomena can inform the anti-scaling techniques and further it will contribute to an improved scale management in the oilfield.
Many of the well-established techniques are used for scaling studies. The main techniques enable investigation into the physicochemical processes that occur on the surfaces and provide information related to the bulk phase of the system and/or the surface kinetics. Relevant techniques include: Tube blocking tests, In-situ flow rig, Quartz Crystal Microbalance, Rotating Cylinder Electrode, Electrochemical methods and modern, dynamic techniques such as Synchrotron X-Ray Diffraction. The formed deposits are analyzed with high accuracy techniques such as the FTIR (Fourier Transform Infrared Spectroscopy) and the deposits are observed with SEM (Scanning Electron Microscope) or AFM (Atomic Force Microscopy).