Formatted Title
Heat and Pressure Tracer Tests in Fractured Sandstone Prior to a Permanganate Pilot Test
Background/Objectives
As part of the planning for a feasibility test for permanganate delivery into a Cretaceous fractured porous sandstone rock contaminated with trichloroethene, the injection process was first assessed using warm water as a tracer. The purpose of the thermal tracer test was to assess the interconnected network of fractures forming the flow pathways from the injection location so as to optimize the design of multilevel systems intended to monitor two-stage amendment delivery in the subsequent permanganate injection pilot study for in situ remediation. The monitoring of the breakthrough responses for pressure and temperature also simulating the convection-conduction interactions analogous to the advection-diffusion processes relevant to solutes.
Approach/Activities
To assess the thermal injection test continuously along the length of monitoring wells new temporary multi-level testing methodology was designed deploying multiple pressure and temperature sensors in core holes using FLUTe liners for hydraulic isolation. These were complemented with high resolution (0.001C) temperature logging so as to determine both temporal breakthrough and spatial distribution within the study site aquifer. The initial plan included the use of one existing 4-inch core hole (C10) and three new rock boreholes (one 4 inch and two 6-inch diameters) as monitoring locations across and along the projected flow path. One of the 6-inch holes collapsed at a steeply dipping fracture zone (at approximately 50 mbgs), necessitating the re-drilling and immediate installing of a waterloo multilevel system. An additional location (6 inch) was drilled to supplement the heat tracer test and temporary sensor deployment monitoring system. In addition to testing with continuous core logging, VOC core sampling (COREDFN) and geophysical techniques, all new 6-inch boreholes were also logged with a complete suite of Schlumberger oil industry slim-line tools. Using these data an array of nine to 11 paired sensors was deployed in each borehole with depths individually measured pre and post installation of a blank FLUTe™ liner, the latter used to continuously seal the borehole and isolate the sensors at the targeted depth intervals. Each monitoring interval included a RBR temperature sensor (0.002˚C variability) monitoring continuously at 10 s intervals, paired with a SWS diver™ to measure hydraulic pressure at a 2min sampling interval. From February 6-10, 2 gpm of water at an average temperature of 36˚C (ambient groundwater temperature is 19.5˚C) was injected into the formation over a 5 m interval from 34.1 to 39.0 mbgs at RD35A. In total 43.6 m3 of water was injected adding 3x106 KJ of heat energy into the rock. The FLUTe™ lined boreholes with sensors were sequentially temperature logged 24 hours a day throughout the heat injection period and following 5 days. Logging was paused for a week and then reinitiated at sparser intervals from February 25 until April 8 to track the temperature peak from the pulse injection at the four monitoring locations.
Results/Lessons Learned
The testing pre, during, and post injection produced a large volume of data and processing continues with preliminary results provided. The temporary deployment data are initially examined as ‘change in temperature’ logs from pre injection as well as time-elevation-head (TEH) and time-elevation-temperature (TET) sections. The maximum temperature increase (~0.5˚C, at 37 mbgs) was observed at 6 m from the injection and grew from being very depth-discrete to broader. Temperature increased ~0.016˚C at 57 m and ~0.017˚C and 32 m distant. Assessing breakthrough pressure responses with distance from injection location showed that: a near immediate increase occurred 6m away, while at 32 m and 74 m responded in 60 and 90 min, respectively. However, at 57 m down gradient an increase in pressure occurred throughout most of the borehole at 35 min after injection began, demonstrating fracture network complexity. The combination of continuous temporal logging with sensors at multiple discrete depths and periodic temperature profiling continuously along the length of the boreholes provides unprecedented insights. High resolution temperature sensors allow detection of minute thermal variations and improved our abilities to optimize the design of multilevel systems to monitor amendment deliveries and possible reactions in fractured rock source zones.