Online Journal for E&P Geoscientists

Serry, Amr M.^*1; Aziz, Sabah ¹; Al-Farisi, Omar ¹; Al-Marzouqi, Mariam ¹; Budebes, Sultan ¹
(1) Umm Shaif-FDD, ADMA-OPCO, Abu Dhabi, United Arab Emirates.

Accurate water saturation estimation in thin carbonate reservoirs is one of the major formation evaluation challenges in horizontal wells. This is mainly due to the strong shoulder bed effect of thick dense sections on the resistivity logs recorded in thin porous reservoir layers, particularly in horizontal wells.

The performed work implies correction of the high resistivity log data acquired while drilling horizontal well sections by means of resistivity inversion. This has been achieved by building a forward model for the resistivity data acquired in the deviated section of the overlying reservoir in a water injector well, where the porous section is thick and the shoulder bed effect is minimal.

The Inversion model is based on the relationship of the deep and shallow Laterolog resistivity logs to the neutron porosity log responses measured in the thick reservoir. The established model equations were used to compute deep and shallow resistivity logs in the horizontal section of the thin reservoirs by resistivity inversion using the neutron porosity log. Several wells were used for this purpose and the results were complimented by test data, MDT samples analysis, Dean Stark measurements and core data.

The results obtained confirmed that the resistivity inversion technique is applicable to compute water saturation in both the flushed zone (Sxo) and the un-invaded zone (Sw)values for horizontal well sections drilled across carbonate reservoirs.

The application of the inversion process allows generating resistivity log responses corrected for the tight shoulder bed effects, and providing accurate water saturation estimation.