Efficient formation evaluation in heterogenous carbonate and clastic reservoirs is indispensable for estimating reserves and optimizing the testing and completion scheme of wells. E&P companies rely heavily on open hole logs to acquire a wide spectrum of measurements necessary for this objective. Effective petrophysical analysis provide quantification of key formation elements including, but not limited to, mineralogy, porosity, reservoir fluids saturation and typing, and rock permeability. Nonetheless, well control issues can sometimes pose considerable limitations to measurement acquisition in open hole leading to partial or complete compromise of data acquisition programs and subsequent loss of essential information. In such case, acquiring alternative measurements specifically designed to work in cased-hole environment is the only mitigation strategy.

A widely known cased-hole logging solution is pulsed neutron measurements that have been introduced to the Oil and Gas industry decades ago. Recent advances in pulsed neutron tools technology greatly improve the quality of this type of cased-hole measurement and enrich the spectrum of its applications, bringing it closer to open hole logs in terms of robustness. In time domain, the measurement includes formation Sigma, for saturation in saline environment, thermal neutron porosity (TPHI), and inelastic fast neutron cross section (FNXS) for gas identification. In energy domain, the measurement includes Inelastic-Capture elemental yields for mineralogy and Total Organic Carbon (TOC), and Inelastic Carbon & Oxygen ratio for salinity-independent saturation estimation.

These advanced measurements were deployed in a mature field to compensate for the absence of open-hole logs by providing comprehensive set of inputs for complete petrophysical analysis. The measurement was additionally implemented to evaluate the gravel pack integrity in certain producer wells that targeted clastic reservoirs where this type of completion is utilized.

The study presents the results of this successful deployment and discusses the associated interpretation workflow that helped optimizing the testing/completion design and characterizing the reservoir fluids across different formations. The study will also discuss the workflow used for verifying the gravel pack integrity with the same measurement.

You can access this article if you purchase or spend a download.