Summary
Pore-scale X-ray computed microtomography (XMT) images were obtained at a
variety of oil (hexadecane) throughput values after gel placement in cores
[involving a pore-filling Cr(III)-acetate-hydrolyzed polyacrylamide (HPAM)
gel]. For each pore in our image volume, we followed oil and water saturations
as a function of oil throughput. These studies were performed both in water-wet
Berea sandstone and in hydrophobic porous polyethylene cores. In hydrophobic
porous polyethylene, oil saturations increased and gel was destroyed
(presumably dehydrated) quite quickly in the smallest pores. Also, oil
saturations increased and gel was destroyed quickly in the largest pores. In
contrast, oil saturations rose much more gradually for the most common or
intermediate-size pores (around 10−4 mm3). The minimum in
oil saturation vs. pore size may result from a balance between gel dehydration
by oil film growth vs. gel extrusion.
In contrast, in water-wet Berea sandstone, increases in oil saturation
occurred evenly over all pore sizes (10−6 to 0.02 mm3)
for all oil throughput values. Consistent with imbibition and drainage studies
performed before gel placement, oil apparently had equal access to Berea pores
of all sizes and, thus, uniformly dehydrated gel in pores of all sizes. Gel
extrusion did not appear to be significant in the Berea pores.
Introduction
An ability of gels to reduce permeability to water much more than that to
oil is critical for successful applications of gel treatments in production
wells if hydrocarbon zones are not protected during gel placement (Liang et al.
1993; Sydansk and Seright 2007). If gelant penetrates into an oil zone and gel
forms, some time will be required before the oil penetrates through the gel
bank and significant restoration of permeability to oil can occur (Seright
2006, 2009). The dependence of permeability on oil throughput determines how
long it takes for a production well to restore productivity after a gel
treatment.
In our previous work, XMT was used to establish why pore-filling
Cr(III)-acetate-HPAM gels reduced permeability to water much more than to oil.
Our results suggest that permeability to water was reduced to low values
because water must flow through gel itself, whereas oil pressing on the gel in
a porous rock forced pathways by dehydration—leading to relatively high
permeability to oil. Those studies involved obtaining 3D pore-level X-ray
images at the saturation endpoints (e.g., after forcing 20 pore volumes (PV) of
oil or water through the core following gel placement). To understand the rate
of restoration of permeability to oil after a gel treatment, we are interested
in how the gel dehydration process progresses as a function of oil throughput.
This study uses XMT to understand the throughput dependence of oil permeability
after gel placement.
© 2009. Society of Petroleum Engineers
View full textPDF
(
550 KB
)
History
- Original manuscript received:
8 February 2008
- Meeting paper published:
20 April 2008
- Revised manuscript received:
26 June 2008
- Manuscript approved:
21 August 2008
- Published online:
16 July 2009
- Version of record:
28 September 2009
View Cart
