With a world context of high oil prices and a rate of increase in reserves from new discoveries, that is not enough to compensate the rate of extraction, in addition to the high maturity of oilfields currently being developed in Argentina, companies have been working to improve the recovery factor of reserves, as a strategy to extend the useful life of the existing assets. Working in this direction, radial drilling technology seems to be an alternative, which, in spite of the fact that it currently raises uncertainty since it has never been tested in the past in or country, can be adapted to the existing wells thus becoming a low investment alternative. The technology involves drilling lateral horizontal bores of small diameter and up to one hundred meters long, with the possibility of placing several within the each productive layer. The laterals are made in two steps: First, the casing is perforated with a ¾" mill and then the lateral extension is carried out by high pressure water jetting. For this evaluation, pilot tests were performed in different oilfields, with the intention of covering a wide range of possible scenarios and being able to evaluate the best applications for this new alternative. The selected scenarios and the different basins are the following: Golfo San Jorge Basin:Mature Oilfields: already exploited formations with production below the economic limit.Viscous Oils: Formations with high viscosity oil and low mobility. Neuquén Basin:Mature Oilfields: low production formationsPrecuyano Formation (altered ignimbrites) of low permeability, with possible micro-fissures to improve net production.Water Injection: To increase secondary recovery improving the sweeping of the formation. This work shows the different experiences undergone by Repsol YPF in Argentina with this technology as well as shares the results obtained and the lessons learned. Introduction It is extremely important to have the possibility of increasing production and raising usable reserves from the known horizons; due to these facts, the search for new technologies to increase production was started, and it was then that the radial drilling technique appeared as a promising one.(Ref 1, 2 and 3) This process consists in making small diameter horizontal perforations by using water jets at high pressure (jetting). The diameter of these lateral horizontal perforations is of approximately 2 inches (5,08 cm) and up to 330 ft (100 m) of extension each, at the same productive level. Each one has a bending radius as small as 1 ft (30 cm) and is made in two steps: first, the casing is perforated with a 0.75-inch mill (19.05 mm), and then the horizontal extension is made with high-pressure fluid jetting (Figs. 1 and 2). This application combines the following important factors:Low cost, it is applied to existing wells (new wells are not required).Low geological uncertainty.Low environmental risk. Among various reasons for this technique to increase production, the following could be highlighted (Ref. 1):Improves the conductivity of an important area around the well (improving drain efficiency).Possibility to define direction of the perforations.Helps the mobilization of viscous oils.Connects to areas of better petrophysical conditions.Allows intervention of oil reservoirs limited by close-by aquifers.

The Chihuido de La Salina field is located in the folded thrust belt of the Neuquén Basin in west-central Argentina, about 200 kilometers northwest of the city Neuquén (Figure 1). The field contains several fault blocks, which produce both oil and gas. Generally, production is controlled by a thrusted anticline, structurally high in the north and relatively low to the south. The most important portion of the field produces oil from the steeply dipping flanks. Efficiently drilling the swelling clay formations of the Neuquén group (Upper Cretaceous), in Chihuido de La Salina field (ChLS), has been a distinctive challenge and is the subject of this paper's analysis and multiple-well case studies. Clay Mineralogy To better understand the clay swelling issues in Chihuido de La Salina field, a basic review is provided of the Neuquén group shale formations. The group consists of terrestrial sediments (Figure 2) laid down during the Rio Grandico sedimentary cycle (Upper Cretaceous). The formations contain two main shale constituents including smectite (70%) and illite (20%). In the smectite shales, montmorillonite is the most critical mineral with regards to swelling. If an atom of aluminum (Al3+) is replaced by an atom of magnesium (Mg2+), it will cause an additional electron or negative charge (Figure 3). The net negative charge is compensated by cation adsorption on the surfaces of the external/internal structure and is likely to cause a phenomenon know as "exchangeable clay cations." These charged cations can be either an ion of sodium (Na+) or a double charged ion of calcium (Ca2+) or magnesium (Mg2+). This reaction produces either sodium montmorillonite, calcium montmorillonite and/or magnesium montmorillonite. The change in clay mineralogy reduces the strength of the repelling forces between layers allowing water to enter and occupy the intra-layer space. Smectites have an expandable structure which increases colloidal activity due to a significant increment of specific surface. All of the structure's surfaces, including intra-layers are available to hydration and cationic exchange. These characteristics give montmorillonite the capacity to swell between layers due to hydration (Figure 4). Although illite clays have the same basic structure as montmorillonites, they don't normally display the same swelling characteristics. In Chihuido de La Salina field, the 8–1/2" hole section must be drilled through formations that contain 70% of the problematic smectite shale constituent, negatively impacting drilling economics. Background - Drilling the Neuquén Group Initial field development began in 1995 using water base mud (WBM). Despite the presence of a potassium chloride inhibitor in the mud, the operator was experiencing severe lost-time incidents related to swelling clay formations in the 8- 1/2" hole section including excessive trips to ream, wash-over, free stuck pipe and in the worst case scenario, sidetracking due to BHA lost-in-hole. To help improve field economics, the operator began utilizing oil base mud (OBM) in 2003 significantly reducing the clay swelling issues. However, it became necessary to increase the mud weight to 10–11 ppg in order to stabilize the hole and limit salt intrusion into the wellbore slightly reducing drilling efficiency. In spite of the OBM success, environmental issues forced the operator to return to WBM in 2006, resulting in the same lost-time incidents previously associated with the swelling clay formations in the Neuquén group.