Abstract
Borehole images acquired in low-resistivity formations can help in the analysis of structural dip, fracture systems, depositional environments, borehole stability, and net-pay identification in thinly bedded sequences.
Net-sand analysis from these resistivity borehole images—in conjunction with results from a multicomponent induction logging service—helps to determine an accurate net-pay, even in thinly bedded intervals.
Laminated formations frequently exhibit electrical anisotropy where resistivity measured perpendicular to the bedding (Rv) is significantly higher than resistivity measured parallel to the bedding (Rh). This occurs when high-resistivity sand layers are interspersed with low-resistivity shale layers.
Analysis based on conventional resistivity tools will often bypass pay zones in thinly bedded sand-shale sequences. Average resistivity over these tools' vertical resolution can be misleadingly low and computed water saturation pessimistically high. This is a major cause of "low-resistivity pay" in thinly bedded laminated formations.
The multicomponent induction logging service is designed to efficiently and economically identify and quantify hydrocarbons in laminated, low-resistivity pay zones. It enables the determination of Rh and Rv. These resistivity measurements, when utilized with the laminated sand-shale analysis and stable tensor petrophysical model, enable the determination of the true formation resistivities and water saturations, and thus lead to accurate identification, and quantification of hydrocarbons-in-place (OIP).
In the Niger Delta where a comparison was made between the Water Saturation computed from Conventional and Multi-Component Resistivity, there was a 30% reduction in the computed Water Saturation, which gave a substantial increase in the computed OIP.
