Bubble coalescence and the effect of electrolytes on this phenomenon have been previously studied. This interfacial phenomenon has attracted attention for reactor design/operation and enhanced oil recovery. Predicting bubble coalescence may help prevent low yields in reactors and predict crude oil recovery. Because of the importance of bubble coalescence, the objectives of this work were to improve the accuracy of measuring the percentage of coalescing bubbles and to observe the interfacial gas-liquid behavior. An experimental setup was designed and constructed. Bubble interactions were monitored with a visualization setup. The percentage of air bubble coalescence was 100% in distilled water, about 50% in 0.1 M sodium chloride (NaCl) aqueous solution, and 0% in 0.145 M NaCl aqueous solution. A reduction of the contact gas-liquid area was observed in distillate water. The volume of the resulting bubble was the sum of the original bubble volumes. Repulsion of bubbles was observed in NaCl solutions exceeding 0.07 M. The percentage of bubble coalescence diminishes as the concentration of NaCl chloride increases. High-speed video recording is an accurate technique to measure the percentage of bubble coalescence, and represents an important advance in gas-liquid interfacial studies.
This paper shows the results of a successful application of the addition of hollow glass spheres, also known as glass bubbles, as a density reducing agent in a drilling fluid. In this field application, glass bubbles were used in combination with an oil based drilling fluid (Core-Drill-N). It was corroborated that the fluid-glass bubble mix is stable, homogeneous, and is compatible with conventional mud motors, bits and surface cleaning equipment.. The system has good rheological and filtration control properties and is suitable for drilling low pressure reservoirs, low permeability and pay zones. During this field application in the well MOT-25B in Venezuela, the density of the base fluid was maintained between 7.1–7.3 ppg (near balance condition) with calcium carbonate as bridging agent. This technology is an alternative to the use of aerated fluids where the reservoir requires a fluid density between 6.0–7.5 ppg, offering some economical and technical advantages due to the elimination of surface compressing and air injection facilities, and to the simplification of operations required to avoid excessive overbalance during drillpipe trips. Additional potential benefits of this low-density fluid include torque reduction as a result of higher lubricity, higher penetration rates and decreased formation damage due to lower invasion of drilling fluid. Glass bubbles are also an alternative to decrease the density of water based drilling fluids, polymer-based fluids, emulsion systems and brines. Laboratory tests were also carried out with different concentrations of glass bubbles in order to evaluate potential field substitutes for aerated fluids in wells which might require lower density fluids. Several formulations for the systems mentioned above were developed with the purpose of achieving maximum density reduction without affecting some mud properties. Fluid density as low as 6.0 ppg was obtained from a 100% oil base mud. Introduction In the last few years in Venezuela there has been an increase in the drilling activities in low-pressures reservoirs with low-permeability, where the utilization of drilling fluids with a density higher to the required could result in a partial or complete loss of fluid into the formation. An excessive level of overbalance could cause effects such as an increase in drilling costs, potential fracturing of the formation, formation damage, and finally potential well loss. The drilling of the above mentioned depleted reservoirs require the use of lower density fluids with specific gravity less than 1 (8.33 ppg). These fluids, in principle would allow maximum extraction while minimizing damage to the producing formation. This work shows the results of the application of glass bubbles as a density reducing agent in an oil base drilling fluid under near balance conditions in an inclined well, drilled in Motatán field in Western Venezuela. Fig. 1 shows Motatán field, in Western of Venezuela. Motatán field is characterized by reactive shale, depleted formations and highly fractured reservoirs with high axial stresses, known for deferred oil production due to flushing by lost circulation. This reservoir has a typical range for matrix permeability from 50 to 100 mD. Porosity in this area is 14% approximately. In addition, this paper presents laboratory test results and the first field trial of the 100% oil system with mineral oil as the base and glass bubbles as the density reducing agent in a drilling fluid. The fluid was used for drilling the 8 1/2" section of MOT-25B well, with an estimated BHT of 250°F. MOT-25B was a deviated well. Drilling with this fluid began at 8275' and reached an Eocene objective at 10,100' (Misoa: B-0/B-4 sand). The density range was 7.1 ppg to 7.3 ppg with 15 ppb using calcium carbonate as bridging agent.
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