This communication describes preliminary results and observations of a successful application in a field environment that incorporated hollow glass spheres, also known as glass bubbles, as a density reducing agent in a drilling fluid. In this field application, a proprietary oil-in-water emulsion fluid developed by PDVSA-INTEVEP which contained hollow glass bubbles (3M) was used during the drilling of a producing interval. The oil-in-water emulsion provided a suitable fluid base, whereas the glass bubbles, by virtue of their low density, imparted a lower finished density than that of the corresponding base fluid. The density lowering capacity of the glass bubbles is proportional to the concentration of bubbles incorporated in the fluid. The field trial substantiated that the fluid-glass bubble pair is stable, homogenous, and compatible through conventional mud motors, bits, surface cleaning equipment, and of such rheological and filtrate properties, as to lend itself to be used in low pressure reservoirs and in producing zones of high permeability. During this field application, we were able to lower and maintain the density of the base fluid at 7.1 PPG. Additional oil production increase was observed relative to a vicinal well (vs. GF-134D) drilled with oil based fluids at an excessive overbalanced. This observation may suggest that damage to the producing zone has been avoided. This technology is an alternative to the use of aerated fluids, with potential economic and technical advantages due to the elimination of surface compressing and air injection controller equipment, and to the simplification of operations required to avoid excessive overbalance during pipe trips. Other potential benefits of using this low density fluid includes torque reduction as a result of higher lubricity, reduction in casing wear, higher penetration rates, decreased formation damage, lost control mitigation, and the use of mud pulse MWD tools. Glass bubbles are also a viable alternative to reduce the density of water based drilling fluids, oil and polymer-based fluids, and brines. Laboratory tests were also carried out with conventional fluid systems to include water-based, 100% mineral oil and oil-in-water emulsions, with different concentrations of LITEDEN™ in order to evaluate the potential field use of such formulations as 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 filtrate control or rheological properties. Fluid densities as low as 5.5 and 6.0 ppg were obtained for corresponding 100% oil and O/W emulsions based fluids. Introduction In the last few years there has been an increasing necessity to drill deposits which have entered a partially depleted stage because of extended years of production. Excessive levels of overbalance pressure can increase fluid invasion. Differential sticking is a costly common problem associated with fluid invasion. In principle, loss of fluid allows the deposition of drilling fluid solids as a filter cake on the well bore. With further filter cake growth, the drill string and drill collars continued to be pulled against the side of the well bore. With time, mud filtrate flows further, building and accumulating solids around the tubulars, and preventing the pipe from moving. The drilling of the above mentioned depleted deposits requires the use of lower density fluids with specific gravity less than 1 (8.33 ppg), such as mist, foam, and aerated or nitrified muds (Figure 1B). These fluids, in principle, would permit maximum extraction while minimizing damage to the producing formation from filtrate or solid invasion. However, there are limitations in the available fluids aimed to operate in a depleted reservoir.
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.
fax 01-972-952-9435. AbstractThis document presents the drilling operations protocol designed to reach a depleted limestone carbonate reservoir, located in the Borburata Field in Southern Venezuela (Fig 1), with the use of a new viscoelastic fluid developed by PDVSA Intevep. This limestone reservoir has a very low pore pressure (about 3.0 ppg equivalent density) and it is characterized by vugular porosity and micro-fractures. Previously, when drilled with conventional fluid systems, severe fluid losses occurred; therefore, the best available alternative was Under Balanced Drilling (UBD) 1 . However, UBD service was a heavy burden on the drilling costs and represented a more complex and risky operation than using a conventional drilling fluid system. In order to have an alternative to UBD, a water-base viscoelastic fluid system was designed to avoid fluid losses in an adverse environment of very high overbalance (about 3,000 psi), very high temperature (about 300°F) and variable pore size due to the presence of vugs and microfractures. Viscoelastic drilling fluid systems have been used because they have excellent fluid loss control properties. However, for this application, the commercial viscoelastic fluids available did not comply with the extreme conditions found in this reservoir. A new formulation specifically designed for these severe conditions was proposed, tested in the laboratory, and evaluated in the field. It resulted in the elimination of fluid losses and allowed the access to this complex reservoir without requiring the UBD service. This result represents significant savings when compared with previous wells drilled in the same reservoir.
fax 01-972-952-9435. AbstractThis paper presents operational results of the pilot test under near balanced conditions of a new foam drilling fluid developed by PDVSA-Intevep in an inclined well drilled in La Paz Field in Western Venezuela. The target formations were a fractured, depleted limestone formations of low pressure, and the reservoir contains highly fractured and hard rocks, known for deferred oil production due to flushing by lost circulation. Similar wells drilled with aerated fluids in the vicinity have shown very low rates of penetration, short bit lives, and instability drilling fluid in presence of contaminants such as salts and crude oil. Results indicated that the foam formulation provided a high stability in presence of crude oil and cement contaminations, and an excellent cleaning capacity in a 12-1/4" hole wherein minimum annular velocities of 45 ft/min were obtained. The physico-chemical properties of the foam allowed regenerating the fluid 76 times with minimal amount of additives. Besides, the average rate of penetration was greatly increased compared to wellbores drilled conventionally and the bit used lasted much longer than in a conventional well in the same reservoir. Finally, this formulation specially developed to withstand high volumes of contaminants proved to be an excellent drilling fluid for near or underbalanced operations with adequate characteristics and very good performance.
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