Close Monitoring of Gel Based Conformance Control by NMR Techniques

Abstract

Carbonate's extreme heterogeneity in the form of fracture corridors and super-permeability thief zones challenges the efficient sweep of oil in both secondary and tertiary recovery operations. In such reservoirs, conformance control is crucial to ensure injected water and any EOR chemicals optimally contact the remaining oil with minimal throughput. Gel-based conformance control has been successfully applied on both sandstone and carbonate reservoirs. However, in-depth conformance control in high temperature reservoirs is still a challenge, due to severe gel syneresis (expulsion of a liquid from a gel) and the associated significant reduction in gelation time. Recently, we have demonstrated the potential of a selected gel formulation and its favorable impact on sweep efficiency for both water and chemical flooding applications in high temperature and high salinity carbonates (Wang, 2016). In the current work, the performance of polyacrylamide/chromium gel injection followed by water flooding for Arab-D carbonate reservoir rock was closely monitored by 1D T2, spatial NMR T2 mapping and 2D NMR techniques. The NMR measurements before and after waterflooding with and without pre-injection of gel provided the detailed description of spatial oil recovery along the rock core sample under reservoir condition. By comparing the spatial T2 distributions from the experiment with waterflooding and gel injection followed by waterflooding for the core sample with artificial wormhole drilled in the center, which mimics the fluid thief zone, the efficiency of the conformance control by gel was measured. The incremental oil recovery factor of ~14% OOIC after gel injection followed by waterflooding was observed throughout the whole sample with highest recovery in the vicinity of where the wormhole begins near fluid injection inlet. In addition, by analyzing the alteration of spatial NMR T2 and T2-D distribution, the accurate flow paths of the injected water and gel were derived from NMR data. The results of the current study increase the understanding of how gel could helps to increase sweep efficiency of waterflooding and other IOR/EOR applications in the presence of unwanted highly permeable channels in the reservoir rocks.

A review on the applications of nuclear magnetic resonance (NMR) in the oil and gas industry: laboratory and field-scale measurements

“…Moreover, on the reservoir scale, NMR logging is used to determine the in-situ oil saturation (Kwak et al 2017;Zhao et al 2020a, b). NMR can provide continuous profiles of the oil saturation due to the high acquisition speed of the NMR tool (Mitchell and Fordham 2014).…”

“…NMR spectrometers are categorized based on the magnetic field strength and the common experiment conducted in each type as follows: High-field NMR (B o , > 3 T), Intermediate-field (1 T < B o < 3 T), and Low-field (B o , < 1 T) (Mitchell et al 2013). High-field NMR are usually used in chemistry (usually used to elucidate molecular and solid structure) that contain cryogenically cooled superconducting components to generate strong magnetic field with high sensitivity (Ladd et al 2018;Moser et al 2017;Richardson 1999). This magnet is large in size costing more than $1,000,000 and requires routine and intensive maintenance.…”

A Characterization of Tight Sandstone: Effect of Clay Mineralogy on Pore-Framework

“…NMR is an alternative to quantify bulk micro-pore systems and system variations in tight rocks (Chen and Balcom, 2006). Based on NMR measurements, pore volumes of micro-, meso-, and macro-pore systems in sandstones can be determined by analyzing T 2 cutoff values (Mitchell et al, 2014;Kwak et al, 2017). The threshold or T 2 cutoff is the intersection value between 1) the cumulative curves of NMR T 2 fully brine saturated, and 2) the NMR T 2 after drainage process.…”