George Sedgwick

Imaging of sand production in a horizontal sand pack by X-ray computed tomography

A laboratory experiment was performed to better understand how sand production can increase heavy oil recovery. A horizontal sand pack with an orifice at one end modeled the production of oil and sand into a perforation in a vertical well. The sand pack was scanned using X-ray computed tomography (CT). The CT images revealed that a high-porosity channel (wormhole) formed in the pack while sand was produced. The wormhole followed regions within the pack where the porosity was higher, and, consequently, the unconfined compressive strength of the sand was lower. This experiment suggests that wormholes will form within the weaker sands of a formation. The development of these high-permeability channels increases the drainage of the reservoir, which leads to higher oil recovery.

Simulation of Cold Production in Heavy-Oil Reservoirs: Wormhole Dynamics

Cold production is a recovery process used in unconsolidated heavy oil reservoirs in Alberta and Saskatchewan, Canada. In this process, sand and oil are produced together under primary conditions. Oil production rates can typically increase by one order of magnitude when sand is produced. The production of sand into a perforation in a well was modelled experimentally using a horizontal sand pack. Heavy oil flowed through the sand and out the orifice at one end of the pack. The pack was imaged using an X-Ray CT scanner. A high porosity channel or wormhole was observed to develop in the sand pack above a critical pressure gradient at the orifice. The wormhole developed in the higher porosity region of lower cohesive strength and broke through to the inlet. The sand cut was 44% (by volume) as the wormhole was developing. When the wormhole broke through to the inlet, the sand cut declined sharply (power law function of time). CT images of the sand pack showed that the loose sand within the wormhole started to be scoured evenly at the top of the channel at this time. The experiment confirms previous assumptions that wormholes can develop in un-cemented oil sands leading to high oil production rates due to greater drainage of the reservoir. The experiment indicates that the weaker part of a sand formation (lower cohesive strength) may be more susceptible to wormhole development. Field observations of the sand cuts of wells on cold production are consistent with the experimental observations. The decline in sand production in these wells, from typically 40% during the initial stage to approximately 3% over a few months, suggests that the main wormholes have stopped growing. The residual sand cuts are postulated to be due to the scouring of the sand within the wormhole.

Seismic monitoring of water floods? A petrophysical study

Seismic velocities were measured in the laboratory on 67 samples as a function of pressure and temperature when saturated with gas and a 35° API = 141.5/(density at 1 atmosphere and 60°F) − 131.5] mineral oil and flooded with pentane and fresh water, respectively, using an ultrasonic pulse transmission method. The rock samples consisted of 39 carbonate cores from eight reservoirs, 22 sandstone cores from six formations, and six unconsolidated samples from three origins. The results show that water flooding increases the compressional velocity Vp by more than 5 percent in most of the gas‐saturated cores at effective pressures (overburden pressure minus pore pressure) less than 20 MPa. Such Vp increase is less than 5 percent in about half of the carbonate cores and some of the sandstone cores with normal pentane and in all the consolidated cores (both carbonates and sandstones) saturated with the 35° API oil. However, in unconsolidated samples saturated with gas, pentane, or oil, water flooding increases th...