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Scale deposition in oil and gas wells is still a major issue in the oil and gas industry as it reduces hydrocarbon production, restricts well access to production logging tools and, in addition, causes safety issues due to blocking and ineffective operation of chokes and valves. Scale is predominantly controlled with chemical scale inhibitors and the most common methods to control scale deposition are through continuous injection and scale squeeze treatments although solid inhibitors can be deployed in ratholes, hydraulic fractures and gravel packs. Non-chemical methods can also be applied and are becoming more common over the last few years especially for calcium carbonate control.Scale management is clearly still a very important factor for the good health of existing oil and gas wells and the trend towards net zero will only increase this reliance as the need for maximum production from existing assets becomes more pertinent compared to the alternative of developing new fields which will be more carbon intensive.Existing scale management strategies will also have a CO2 footprint and scale control methods will be reviewed to become more aware of this and to highlight how certain areas of scale management can become more effective and adapt to the changing needs of the energy industry such as the increasing use of enhanced oil recovery (EOR) in both conventional and unconventional fields.The review will include several areas of scale management including scale prediction risk, chemical and non-chemical treatments, scale inhibitor chemistry from renewable sources, monitoring techniques coupled with improved data processing techniques and automation.The drive towards net zero has also instigated the development of alternative energy sources to fossil fuels which have resulted in a major focus on projects in geothermal energy and increased the potential for carbon capture, utilisation and storage (CCUS) projects where CO2 captured from heavy industry is transported to site and injected into geological reservoirs for storage and/or enhanced oil recovery.Scale control will be important to both geothermal and CCUS projects and this paper will highlight examples including scale control in geothermal wells with options for treatment and desirable chemical properties and carbonate scale control in CO2Water Alternating Gas (WAG) injection whilst also demonstrating CO2 storage and enhanced oil recovery (CCUS). In addition, the potential for halite deposition and carbonate mineral dissolution and its impact on rock mechanical integrity during CO2 injection into hyper saline aquifers and depleted oil and gas reservoirs will be discussed.
Scale deposition in oil and gas wells is still a major issue in the oil and gas industry as it reduces hydrocarbon production, restricts well access to production logging tools and, in addition, causes safety issues due to blocking and ineffective operation of chokes and valves. Scale is predominantly controlled with chemical scale inhibitors and the most common methods to control scale deposition are through continuous injection and scale squeeze treatments although solid inhibitors can be deployed in ratholes, hydraulic fractures and gravel packs. Non-chemical methods can also be applied and are becoming more common over the last few years especially for calcium carbonate control.Scale management is clearly still a very important factor for the good health of existing oil and gas wells and the trend towards net zero will only increase this reliance as the need for maximum production from existing assets becomes more pertinent compared to the alternative of developing new fields which will be more carbon intensive.Existing scale management strategies will also have a CO2 footprint and scale control methods will be reviewed to become more aware of this and to highlight how certain areas of scale management can become more effective and adapt to the changing needs of the energy industry such as the increasing use of enhanced oil recovery (EOR) in both conventional and unconventional fields.The review will include several areas of scale management including scale prediction risk, chemical and non-chemical treatments, scale inhibitor chemistry from renewable sources, monitoring techniques coupled with improved data processing techniques and automation.The drive towards net zero has also instigated the development of alternative energy sources to fossil fuels which have resulted in a major focus on projects in geothermal energy and increased the potential for carbon capture, utilisation and storage (CCUS) projects where CO2 captured from heavy industry is transported to site and injected into geological reservoirs for storage and/or enhanced oil recovery.Scale control will be important to both geothermal and CCUS projects and this paper will highlight examples including scale control in geothermal wells with options for treatment and desirable chemical properties and carbonate scale control in CO2Water Alternating Gas (WAG) injection whilst also demonstrating CO2 storage and enhanced oil recovery (CCUS). In addition, the potential for halite deposition and carbonate mineral dissolution and its impact on rock mechanical integrity during CO2 injection into hyper saline aquifers and depleted oil and gas reservoirs will be discussed.
Calcium carbonate is a pH dependent inorganic mineral scale that is influenced by CO2 and H2S partitioning. CaCO3 prediction must therefore include accurate modelling of the aqueous phase and all hydrocarbon phases present. pH dependent scale prediction challenges and the development of a rigorous procedure for generation of more accurate results were previously published. This procedure has now been applied to an onshore oilfield in Southeast Asia for assessment and management of CaCO3 scaling. A rigorous scale prediction workflow was applied to ‘at-risk’ field producers that showed CaCO3 scaling at and/or downstream of the wellhead choke valve (WHCV). By inputting relevant field data into an integrated PVT/scale prediction code and using the correct procedure, it was possible to evaluate scaling potentials. A series of sensitivity studies allowed well ranking based on the predicted severity of their scaling potentials. The approach validated mechanistic hypotheses for scale development in prolific low watercut, ultra-high CO2, sour, high temperature producers. Close matching of predictions with actual wellhead scaling events provided the basis for improved full-field scale management, and strategic targeting of onsite scale mitigation resources. Target field producers exhibited 0.2% to 25% watercut and presented different degrees of scale precipitation at and/or downstream of the WHCVs. Following well scaling potential assessment, each producer was subject to a series of sensitivity studies to identify (i) how scaling changed with time and (ii) provide focus on the key inputs that most impacted predictions. The initial findings, considering measurement errors (normal field variability), were surprising as key input parameters such as gas phase CO2 and produced water calcium ion concentration appeared to show minimal influence on the final scale prediction results for these wells; even more remarkable considering typical production featured very low salinity produced brine and ultra-high CO2 sour field gas. Focus was therefore shifted to field temperatures, pressure profiles and volumetric flow rates. Of importance is that the selection of ‘critical parameters’ is field specific and that the example presented here shows the variability in scale precipitation at different stages of well production, and how the scaling potential (SR and mg/L) must be evaluated together with the predicted daily theoretical mass of scale (kg/d). This is important in the study of wells with such variable water cut. The following paper demonstrates the value of a rigorous and systematic approach to the prediction of CaCO3 scale, which is often investigated using inappropriate or incomplete methodologies. In this work the authors demonstrate how the technique can address and explain important operational issues and provide solid foundations for implementing and indeed improving the field scale management program.
Alkaline-Surfactant-Polymer Flooding (ASP) has the potential to unlock massive oil reserves in quest of production sustenance within the bounds of profitable economics. Field results from a successful ASP pilot targeting the massive Sabriyah Mauddud (SAMA) reservoir in Kuwait, using a regular five-spot with five acre-spacing are encouraging. Oil cut post softened water pre-flushing reached 0% and tracer data indicated pre-mature breakthrough at the central producer. This necessitated in-depth conformance gel treatment1-3 to induce flow under matrix conditions and softened water injection resumed thereafter for a period of ~3 months, during which oil cut ranged between 2 to 6%. Oil cut then decreased to 0% again, beyond which polymer pre-flushing was introduced for a period of ~2 months, during which oil cut was increased to up to ~4%. ASP flooding resulted in an unambiguous and sustainable increase in oil cut with an average of ~12% over a period of more than 6 months. Furthermore, daily oil production rate after ASP flooding more than doubled. Effective oil-water separation of produced emulsion has been established and maintained using fit-for-purpose pre-heating, chemical dosing and gravity segregation technologies, thus resulting in relatively low BS&W levels in separated oil (i.e., <5%). Potential in-situ scale risks were effectively managed by injection an innovative scale inhibition package composed of inhibited glacial acetic acid in conjunction with a phosphonate-polymeric scale inhibitor into the capillary tubing string of the central producer, during which 100% production uptime was achieved for several months3. Field data demonstrated that in-situ scale risks due to ASP injection were originally overstated because scale issues were limited even without injecting the adopted scale inhibition package. ASP reservoir simulation forecasts indicate that oil rates and oil cut should continue to increase. ASP flooding is ongoing to date and continues to generate important operational learnings and priceless field data to evaluate the techno-economic viability of phased ASP flooding commercial development.
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