One of the major challenges of stimulating wells in the San Francisco and Balcon fields in Colombia is adequate fluid placement. The wells in these areas have different zones open to production. Typically, these zones show severe petrophysical contrasts regarding permeability, porosity, and oil-and-water saturations. Permeability can be 25 times greater in one zone than another. Furthermore, these open zones may also have different pressures. These variations in rock and fluid properties increase the probabilities for preferential flow to the zones of less resistance. Therefore, selective stimulation techniques are commonly used to treat wells in these two fields. Single and straddle packers for bull-heading and coiled tubing with conventional nozzles are some of the commonly used techniques.
This paper discusses the results from using CT and a fluidic oscillator as a new alternative to place stimulation fluids. A true fluidic oscillator generates pressure waves using the Coanda effect. These low amplitude, high-frequency pressure waves enhance damage removal and fluid placement through cyclic loading. This technique has been extensively used in the San Francisco and Balcon fields for Hocol in Colombia. Three stimulations using CT and a fluidic oscillator are discussed in this paper as well as the results from this fluid placement technique with conventional placements showing how the use of CT and a fluidic oscillator can increase hydrocarbon recovery.
The San Francisco and Balcon Fields both produce from the Caballos formation (Cretacic). These two fields are located in the Neiva sub-basin in the upper Magdalena Valley, from 15 to 30 miles northwest from Neiva, Colombia. Fig. 1 shows a map of the area and Fig. 2 shows a typical log and a stratigraphic column.
The Balcon, which was discovered in 1988, and San Francisco, which was discovered in 1985 are mature fields. Both fields have a broad range of petrophysical property values. Permeability varies from 200 to 2,000 mD and porosity from 9 to 18% as shown in Table 1. The primary drive mechanism for these reservoirs is solution-gas-drive. Wells in these fields are typically stimulated by bull heading or by running a straddle packer system when the well is worked over. They are also stimulated using CT with conventional jet nozzles. A novel and beneficial approach was taken to use a fluidic oscillator at the end of the CT.
The San Francisco Field is located in the Neiva sub-basin, in the Upper Magdalena Valley. It was discovered in 1985 when the SF-001 exploratory well was drilled. Three additional wells (SF-002, SF-003 and SF-006) where drilled in the first half of that year to confirm the reservoir. An additional 28 wells were drilled during the second half of 1985. It is currently part of the Palermo contract between HOCOL and ECOPETROL.
San Francisco's main reservoir is the "Caballos" formation (KB). This formation has been divided into 12 flow units: 9 on the Upper Caballos formation (UKB) with a total of 77% of the original oil in place (OOIP). The other three flow units are in the Lower Caballos formation (LKB) with 23% of the OOIP.