COMBINING LOGGING-WHILE-DRILLING (LWD) RESISTIVITY AND CAPTURE SIGMA (Σ) TO IDENTIFY AND EVALUATE WATER FLOOD ENCROACHMENT – CASE STUDY OF A FIELD WITH MULTI-LAYERED, COMPLEX RESERVOIRS

摘要

This study focuses on a brown field development where stacked reservoir layers are undergoing secondary recovery via water injection. Certain reservoir layers experience significant water flooding, while other layers experience very little to no flooding. Current evaluation approaches to understand the amount of water encroachment involves production logging and/or production tests. Both approaches are expensive in terms of lost production and data acquisition. Water flooded reservoirs contain an unknown mixture of connate and injected water. As such fixed water salinities cannot be assumed in water saturation (Sw) computations. Water production is a concern, only reservoir layers with hydrocarbon volumes greater than a pre-determined cutoff are to be completed. During the infield drilling program, an innovative approach to enhance reservoir understanding with log data acquired while drilling was implemented to compute water salinities and saturations across the stacked layers. LWD (Logging-While-Drilling) data experiences limited drilling fluid invasion such that relatively shallow depth of investigation (DOI) measurements like capture sigma (Σ), which are sensitive to reservoir fluid chlorine content, can be used to estimate S_w when formation water salinity is known. Likewise, Archie resistivity-based approaches can also be used to compute S_w in environments of known water salinity. In this paper we use LWD logs acquired on multiple wells acquired across multiple layers to demonstrate a simultaneous inversion of ? and resistivity to evaluate reservoir water salinity and saturation. In these examples the reservoir environment consists of unknown and/or mixed water salinity. We show that the simultaneous inversion approach correctly identifies changes in formation water salinity and saturation while the conventional resistivity approach over-estimates hydrocarbon saturation and can lead to errors in the completion of zones with high water cut.