Abstract
The La Rosa Basal Sand (Miocene), known in some areas as Santa Barbara Member, was discovered in 1954 as a pool for Block I area in Lake Maracaibo basin, with a relatively poor success during the next 40 years of production.
Since 1993 however, an aggresive policy of workovers and drilling was undertaken increasing by over 300 % the total production of medium and light oil. These activities were based upon the recommendations of several multidisciplinary team projects.
The La Rosa Basal Sand is a 5–60 ft thick sandstone deposited in a fluvio deltaic environment overlaying an unconformity which truncated Eocene succesions (Pauji and/or Misoa formations). Lateral continuity varies from south to north and it is feasible not only to observe new sand bodies but also coalescent effect with the underlying Eocene productive sands. The La Rosa Basal Sand is overlain by a 100′–200′ thick marine shale, known as La Rosa Shale.
Change of paradigm in the reservoir management was mainly a consequence of the result of well VLA-1185, upon the west flank of the Block which also demanded a revision of the petrophysical parameters. Its initial production of 1,300 BPD and 0.3 % water, was difficult to explain considering resistivity values of only 8–10 Ohm-m, a parameter which had been long considered to indicate high water saturation. Such parameter subestimated remnant reserves and in some cases supported rejection of some well locations. Additionally new core data has helped to better understand reservoir behaviour and predict future activities. During the last four years seismic interpretation, stratigraphic well by well correlation, structural and isopach maps and production history matching have been updated by information from new wells which have acted as a support for a slimhole campaign. Consequently, geologically targeted infill wells and no conventional workovers, increased production from 4000 BPD to 18400 BPD (Mid, 1996).
