Hydrocarbon Saturation Evaluation Behind Gravel Packing and Complex Completion Through Advanced Pulsed Neutron Logging

Abstract

Abstract Gravel packing in the annulus between the screen and casing ensures the production of reservoir fluids without sand production. However, the effectiveness for controlling sand production and the permeability of the pack decreases over the years. It is important to quantify the gravel packing together with formation fluids saturation evaluation for production enhancement opportunities. From pulsed neutron logging (PNL), analysis of the expanded set of elements and minerals at high accuracy allows the quantification of gravel packing and reservoir fluid saturation simultaneously. Between two PNL runs, the background gamma ray (GR) count is subtracted from the activated GR count. The gravel pack log is made from linear response between the good gravel section and the top of gravel or major void. Besides, from inelastic-capture measurements in gravel packs, the normalization of near detector inelastic silicon yield to the sum of silicon and iron yields is another effective gravel pack quality indicator. Later in the processing path for formation evaluation, different environmental corrections and elemental offsets are determined to remove the contribution of gravel pack, different borehole fluid, and casing and cement composition. Ultimately, the integrated interpretation of carbon-oxygen (C/O), Total Organic Carbon dry weight fraction (TOC), neutron porosity (TPHI) and fast neutron cross section (FNXS) enable accurate determination of formation gas, oil, water saturation condition behind gravel pack and casing. In three examples presented in this paper, the gravel pack (GP) quality has been addressed and analyzed based on two different methods: the traditional GR counts difference between activated and not log, and the direct estimate of gravel presence and percentage from raw elemental concentrations being measured by the advanced PNL simultaneously to the other pulsed neutron and carbon/oxygen measurements. Understanding the gravel packing and the contribution from borehole conditions will help to reduce the uncertainties of log response and to compute reliable rock petrophysical properties and fluids saturation in the formation. The prompt evaluation of these gravel pack logs can provide a more accurate understanding of borehole effects on the petrophysical answer. The information can also directly be used to determine the void in gravel pack completions. Further plan for void repair can reduce the formation damage resulting from fluid loss in the formation.