Near Loma La Lata and Sierra Barrosa fields, Lajas Formation thickness reaches up to 1000m of sediment that includes fine to coarse sandstone to subordinated conglomerates with tight features including low porosity and permeability values, 0.001 to 0.03 mD.These reservoirs exhibit significant net pay, 150-300m, with high lithological, petrophysical and granulometrical complexity. An associated feature is the abnormal response of induction logs, resistivity, in some reservoir levels. This anomaly shows significant different values for the same reservoir level, in which the rest of logs don t́ behave the same (GR, PEF, porosity logs, etc). This behaivoir can t́ be explained by lithological changes or flow capacity variations, and historically it has been assigned to several fluids responses; consequently, those levels were left without stimulation. Based on the available cores and sidewall cores data from wells with this behavior, anintegrated analysis ispresented with the aim of find out what is causing the aforementioned anomaly, and to allow adding extra net pay. Petrographic studies, thin sections, X-ray diffraction and MEB, were integrated with petrophysical data and NMR logs, Neutron Magnetic Resonance. Also, Lithological and Icnological studies were used in the core samples.The results allowed to determine that high non-free water proportion included in nano and micropores from clay minerals, may be the cause of low resistivity anomalies. The parameters with highest influence are granulometry, clay content and pore size, more than total porosity. Compaction degree has also an important influence, showing low resistivity values related to warped clay chips and sutured grain contacts.