Abstract
Physical properties of the reservoirs are known to be affected by the dynamic processes dominating during active field depletion. Formation resistivities from the open hole logs are one of the most sensitive measurements influenced by alteration of the reservoir properties due to production. Unusually high resistivity values were noted to occur more frequently with ACG field development. This largely affected water saturation values calculated using Archie model and hence the hydrocarbon volume in place estimates.
Mapping resistivity values across the field revealed the production time dependency of these high readings. A relationship between cumulative oil flux and formation resistivity at irreducible water saturations (away from the water front) was identified based on core experiments from the fields in the similar geological settings and the outputs from the ACG reservoir simulation model. This relationship showed increase of resistivity with the number of pore volumes flushed by oil through the porous medium. Through the systematic analysis of the field data this behavior was determined to be mostly related to the alteration of the wettability as a result of active dynamic processes in the porous medium.
