Pushing the Envelope of Residual Oil Measurement: A Field Case Study of a New Class of Inter-Well Chemical Tracers

Abstract

The success of any improved oil recovery (IOR) project is largely dependent on how much oil is remaining to be mobilized within the targeted area of the partially depleted or mature reservoir. Partitioning tracers are generally used to measure residual oil saturation (Sor) or remaining oil saturation (ROS) in the near wellbore region via a single well chemical tracer test (SWCTT) or in an inter-well region via a partitioning inter-well tracer test (PITT). There is a limited repertoire of nonradioactive and environmentally friendly inter-well partitioning tracers for measuring ROS. A new class of environmentally friendly partitioning tracers was field tested, in a giant carbonate reservoir undergoing peripheral waterflood, for measuring ROS in inter-well regions in a depleted area. The new partitioning tracers were qualified via laboratory experiments and are deemed to be very stable at reservoir conditions (213°F and a salinity range of 60-200 kppm). The field pilot was conducted concurrently with a set of non-partitioning inter-well chemical tracer test (IWCTT) to determine reservoir connectivity, water breakthrough times, and injector-to-producer pair communication in an area selected for an IOR/EOR field pilot. An elaborate sampling and analysis program was carried out over a period of 30 months. This paper reviews the complete design and implementation of the test, operational issues, and the analyses and interpretation of the results. The breakthrough times of the passive and partitioning tracers are reported, and inter-well connectivity between the paired and cross-paired injectors and producers are analyzed. The ROS measured by a majority of the novel tracers is comparable to the saturations obtained via SWCTT, core and log derived saturations. The combination of conventional IWCTT and the novel partitioning tracers via PITT has been very useful in analyzing well interconnectivity, understanding the reservoir dynamics and quantifying remaining oil saturation distribution in the reservoir. This has led to better reservoir description and an improved dynamic simulation model.

3D simulation of active-passive tracer dispersion in polygonal fractured geometries

“…One of our goals is to simulate field-scale tracer experiments (Sanni et al 2016). For this purpose, we generate a three-dimensional fractured geometry using seed points resulting in 2304 Voronoi blocks.…”

“…Choice of a boundary condition (or rule) for a tracer crossing the interface between fracture and matrix is a non-trivial task: its inappropriate choice can significantly degrade accuracy of the 3D concentration field (Szymczak and Ladd, 2003). In our simulations we use specular reflection boundary condition, which is more difficult to program but it provides correct distribution of tracer concentration compared to alternative boundary conditions.…”

Three-dimensional simulation of tracer transport dynamics in formations with high-permeability channels or fractures: Estimation of oil saturation

“…In our analysis, we strive to (a) perform simulations in the diffusion-dominated regime (Pe = 20) and (b) achieve realistic exit times for the distributions of tracers. For orientation, we consider the experimental field data from Sanni et al 5 The authors reported the distance of ∼610 m between tracer injection and detection (injector-producer distance). Their data suggest that the maxima of produced tracer concentrations are at ∼250, ∼350, and ∼450 days for the partitioning coefficients of K = 0, 2, and 4, respectively.…”

“…In tracer injection tests designed to estimate remaining oil saturation, it is common practice to use tracers with several partitioning coefficients K. 5,65 This is done to improve the reliability of the experimentally obtained values of S est o . As our results demonstrate, variation of K within a practical range (K ≈ 2, .…”

“…Fluid tracers can illuminate the flow and distribution of immiscible fluids in the subsurface. These tracers are injected to study natural or artificial processes and systems, such as aquifers, [1][2][3][4] oil 5 and gas 6 reservoirs, as well as morphological and hydraulic properties of soils, 7 and groundwater flows. 8,9 Tracer transport is governed by the principles of chromatography.…”