The Golfo de San Jorge basin, located in central Patagonia, is a multilayer reservoir with complex geology. Because of this, the industry traditionally has relied on conventional swabbing as the most reliable way to determine the production and flow rates of each zone. After the wells are drilled and cased, the potential producing layers are perforated and tested to determine individual zone contribution. The well-testing information is used to select the zones that are plugged, the zones that will produce naturally, and the zones that will be fractured to enhance production.
The conventional method of well testing includes setting a retrievable plug below the zone of interest and a retrievable packer just above the zone of interest; this is performed with a conventional completion rig using jointed pipe. Next, the rig crew performs necessary swabbing until the produced fluids indicate the type of fluids in the formation and the production capacity. The zones to be fractured are isolated by a retrievable plug and packer during the stimulation job. On average, there are 3.15 zones per well that are fractured and 7.6 zones that are tested (swabbed) per well. The completion of these wells takes approximately 10 days because of the number of swabbing tests and fracturing operations performed. This paper documents results of the field trials performed with a new type of straddle-packer system introduced to reduce the time required to complete a well. This straddle-packer system has the capability to perform well tests and fracture treatments without pulling out of the well. In fact, the operator can swab test a zone or all of the zones, proceed with the fracture treatments of selected zones, and then retest the treated zones, all without pulling out of the well.
This technology has proven that it can save a substantial amount of time in the completion and testing phases in the Golfo de San Jorge Basin.
This straddle-packer system is a product of a technology-collaboration agreement between the operating company and the service company. This innovative agreement was implemented to have a systematic way to convert ideas into new products and services needed to raise the productivity, increase operating efficiencies, improve safety, and to reduce the lifting cost of the operating company.
The Cerro Dragon Field is located in the Golfo de San Jorge basin, in the provinces of Chubut and Santa Cruz, Argentina (Fig. 1). It has an area of 3480 km2 and has been exploited since 1958 with approximately 4,000 wells drilled to date.
The Golfo de San Jorge basin is a Mesozoic extensional basin filled with Jurasic, Lacustrian, and Cretaceous fluvial deposits with tertiary compression and wrenching superimposed on earlier extensional features. There are about 30 producing structures, each containing 20 to 50 separate reservoir horizons of 4- to 26-ft thickness. Within many of the structures, there is a high degree of fault-induced compartmentalization. In total, there are more than 9,000 separate, highly heterogeneous reservoir units.1 After the well is drilled, the drilling rig is used to run the 5.5-in. casing and, after the casing is cemented in place, the drilling rig moves out. The wireline service company runs a cement-bond log to determine zonal isolation and, after that, the completion rig moves in to test and complete the well. If the zonal isolation is adequate, then all the potential producing zones are perforated with conventional wireline-casing guns.