In western Venezuela, accesing low-pressure, depleted reservoirs is a challenge that has to be overcome in order to recover high volumes of remnant hydrocarbons, in the area of Lake Maracaibo (Lagomar, T?a Juana and Lagunillas fields, among others). In these fields, the utilization of conventional fluids becomes technically difficult and low profitable, because the hydrostatic pressure exerted by the fluid column is higher than reservoir pressure, causing fluid losses and formation damage, with the following consequences: increase in the cost of workover operations, potential fracturing of the formation, formation damage, delayed production and finally, complete loss of the well. The technology of aerated O/W emulsion for workover operations, is an alternative to solve these problems. The successful application of this technology begins with an adequate selection of the wells and a proper design of the formulation.
This work covers the development, technical features and application of the technology of aerated emulsion utilizing static mixers that allowed to homogenize a triphasic system (air, oil and water) into one phase. This technology also allowed to restore the original mechanical conditions of the well that other conventional systems failed to accomplish. As a consequence, expected production was achieved due to a lower formation damage caused by the workover fluid. Aeration of O/W emulsion represents an attractive choice from the technical-economic viewpoint, having additional advantages in comparison with commercially available systems
One of the problems encountered in Lake Maracaibo, Venezuela is the making of workovers in lowpressurized, offshore reservoirs. This has propelled research activities in fluids capable of accomplishing this requirement. A water-base emulsion fluid, used previously in more than 100 wells in workover operations, was aerated in order to decrease its density from 7,3 to 5,5 ppg, and it was used for workovers in the low-pressure reservoirs already mentioned(1).
This system is based on an oil-in-water emulsion with a density between 7,3 and 7,6. This system has been used successfully from 1996 in many oil and gas producing fields in Venezuela. In the aerated version, bubbles of air have been incorporated to the fluid with the purpose of reducing its density.
Base emulsion is aerated to the required density, increasing the rheological properties of the base fluid. The high rheological properties and the low density of the aerated fluid make this system very suitable for workover operations in Lake Maracaibo's offshore reservoirs. High viscosity improves efficiency of cuttings transport while cleaning the hole and decreases the mobility of the filtrate in the formation. On the other hand, the low density minimizes formation damage due to an underbalance drilling condition, and eliminates circulation losses.
Besides the advantages already mentioned, this fluid has a thermal stability of 280 °F, good transport capacity, resistance to typical contaminants (crude oil, sands, etc), excellent lubricity, low environmental impact and minimum equipment requirements for its formulation and control.
The development of the aerated emulsion technology is based on two aspects. An adequate chemical formulation to stabilize water/oil/gas triphasic systems, and a compact, easy-operated static mixer.
