Control of micro-organisms during the completion of hydraulically fractured wells is a significant component in the successful development of a production system. Detrimental bacteria, such as sulfatereducing bacteria (SRB), introduced into the reservoir during the completion process, can facilitate biogenic sulfide production, resulting in souring of the production fluids and gas, iron sulfide formation, and SRB associated microbiologically influenced corrosion (MIC). Biocides are routinely dosed at low levels into the fracturing fluids to control microbe populations and thus the subsequent adverse effects associated with bacterial activity. Biocides, by their very nature and intended purpose, are not well tolerated by certain aquatic organisms. In an effort to improve the ecological profile of the microbiological control program in fracturing operations, a treatment system using nitrate and nonhazardous live nitrate-reducing bacteria (NRB) for the control of SRB was developed.Nitrate-based mitigation of SRB has been used as an alternative to biocide injection in the oil and gas industry for decades. Successful SRB control using nitrate-based treatment applications has been observed in several waterflooding programs throughout the world. Nitrates stimulate the metabolic activity of NRB. NRB can mitigate SRB activity by means of three primary mechanisms: competition for available carbon sources, direct metabolic inhibition through the generation of nitrite, and certain species of NRB, which directly oxidize biogenic sulfide. This case study is an evaluation of the application of live NRB, selected for their tolerance of the temperature and salinity of the Marcellus shale, and sodium nitrate nutrient solution, as an alternative treatment to the application of biocides for hydraulically fractured wells. Both live NRB and nitrate solution were added into the fracturing fluids during the fracturing operation.Multiple wells were treated in the Marcellus shale using the tested NRB and nitrate treatment system, and these wells were monitored for periods ranging from three to 18 months depending on the date of completion. Treatment efficacy was evaluated by comparing data from the NRB and nitrate-treated wells to data collected from wells completed in the same manner and, in some cases, on the same well pad with a biocide that historically exhibited good microbial control. The results from the wells treated with NRB and nitrate demonstrated that the treatment was similarly effective compared to successful biocide applications for the control of SRB activity.
The purification capacity of systems using floating aquatic plants depend on the climatic conditions under which they are used. This study from Cuban conditions evaluate the effects of the organic loading rate, hydraulic loading rate and water depth on the purification capacity of water hyacinths, as well as the effect of some climatic variables on the kinetics of the treatment processes. The experimental system consisted of two consecutive tanks simulating a system of ponds in series. The water depths used were 0.5 m and 1.12 m. In the shallower system with shorter retention times and greater superficial organic loading higher removal efficiencies are obtained. With the data obtained, empirical relations were sought. From these correlations it is possible to determine the values for some parameters used in the design of aquatic treatment systems with water hyacinths. The results revealed a relationship between the purification capacity of the water hyacinth and its velocity of growth. The specific velocity of growth varied with the months of the year and was associated with the temperature and the solar radiation. A multiple correlation equation describing these relations was obtained.
A new class of expanding isolation systems has been enabled by the creation of a uniquely engineered expanding metal alloy. The engineered metal alloy expands downhole and chemically transforms from a metal alloy into a rock-like seal. This novel metal alloy results in a sealing system that combines the operational simplicity of swellable elastomers with the robustness of non-elastomeric seals and includes an anchoring capability to the seal. Swellable elastomers have provided effective zonal isolation since their introduction in the early 2000s. Swellable elastomers expand by absorbing fluids within the matrix of the elastomer. This absorption causes the swellable elastomer to expand in size and results in a high-pressure seal for zonal isolation. Despite the widespread success of swellable packers, for some applications a non-elastomeric seal for zonal isolation is preferred and more reliable. Applications benefit from non-elastomeric seals for zonal isolation due to temperature, pressure, or chemical compatibility reasons. Other applications, such as fluid injection operations, require anchoring capabilities which can be challenging with swellable elastomers. The new engineered metal alloy chemically reacts with the downhole water-based fluids and expands into a strong rock-like material that provides non-elastomeric zonal isolation with pressure and anchoring capabilities exceeding swellable technology at higher expansion ratios. In addition, water swellable elastomers are not suitable for applications which have a high salinity brine or produced water as the setting fluid. By contrast the expanding metal alloy chemical reaction is enhanced by increasing salinity. The expanding metal alloy bonds with the water-based fluid in the wellbore and this chemical reaction causes the metal to expand into a rock-like material. The chemical reaction results in a new material that is larger than the original alloy. Unlike a swellable elastomer which absorbs fluids (a purely physical process governed by thermodynamics and osmosis), the metal alloy's molecular structure chemically transforms, incorporating the water molecules to create a new material. The metal alloy can expand over 80% as it transforms into its final state as a rock-like seal. Extensive small-scale and full-scale tests were conducted to reliably and consistently map the metamorphosis from the engineered metal alloy into the rock-like material. These tests required developing new methods for testing the material including designing new test fixtures and new test procedures. Testing proved seals were created in smooth cylinders as well as in irregular shapes and with a wide range of brine types and brine concentrations. The result is an expanding engineered alloy that creates a robust and durable seal with anchoring capabilities across a wide range of downhole conditions. A novel non-elastomeric zonal isolation system is composed of a new expanding metal alloy that expands in water-based wellbore fluid, completion fluid, or formation fluid. The performance of this new material has been demonstrated through experimental testing. This paper discusses the development and initial testing of this new expanding metal and the process of forming a robust and reliable downhole seal with anchoring capabilities.
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