To enhance stimulation treatment placement and effectiveness in highly deviated and deep wells, a coiled-tubing intervention was designed and implemented using a fluidic oscillator. The stimulation treatments were developed to mitigate damage caused by fines migration, water blockage, scale, and asphaltenes; such damage is typically located in the near-wellbore area.
Traditionally in southern Mexico, stimulation treatments in highly deviated and deep wells were bullheaded from the surface using diversion techniques. Results from these treatments were not always satisfactory.
A fluidic oscillator was used as a placement technique for these stimulations. This tool, with no moving parts, generates a change in fluid direction that creates a low-amplitude pressure pulse at a frequency range from 300 to 600 Hz.
The synergy from the use of coiled tubing, a fluidic oscillator, and a tailored stimulation treatment was proven effective in stimulating these wells, achieving excellent results.
Case histories from four wells are presented: Samaria 1129, Iride 154, Jujo 654, and Mora 3.
Actual producing well conditions in Mexico's southern region impose challenges that often require the consideration of new technologies. These technologies, combined with high-quality services and excellent job execution efficiency, aid the operator in achieving the best results possible. Fig. 1 is a map of PEMEX's south Mexico oilfields.
PEMEX's southern reservoirs are characterized as being naturally fractured. Because of their high level of exploitation, these reservoirs have low pressures. The fields comprise a system of carbonate reservoirs producing 28 to 38º API crudes associated with an active acquifer and a secondary gas cap. The hydrocarbon-producing formations exhibit a permeability range from 10 to 100 md and porosities from 3 to 18%. Petrophysically these formations are primarily composed of limestone and dolomites with low shale content.
In these fields, the most common near-wellbore damage mechanisms are fines migration, organic and inorganic deposits, and rock-wettability changes. The latter occurs as a result of the fast advance of the oil-water contact and the gas-oil contact. Wettability change represents a special challenge when performing stimulation work. Care must be taken to avoid increasing the oil:water ratio (OWR) and the gas:oil ratio (GOR)
The stimulation work presented in this document was performed using coiled tubing (CT) and a fluidic oscillator (FO).
CT technology has seriously evolved since its first oilfield application in the early 1960s, when the first coiled tubing unit (CTU) was built and used in the oilfield. As technology improved, use of CT became recognized as a reliable, cost-effective, and fast method to perform live well intervention. A significant breakthrough in CT reliability occurred in the 1970s and 1980s, when improved manufacturing quality and continuous milling allowed the fabrication of tubing. Before that time, CT was manufactured in 1,500-ft sections and welded together. Steels of higher strength were used to manufacture the tubing, adding additional durability and strength to the system. Currently, CT can be manufactured from steels with various high-yield strengths and in sizes up to 4.5-in. OD. Fig. 2 shows a land-based CTU working on a well.