The Effects of Layer Permeability Contrast and Crossflow on the Effectiveness of Polymer Gel Treatments in Polymer Floods and Waterfloods
- H.W. Gao (Natl. Inst. for Petroleum and Energy Research) | T.E. Burchfield (Natl. Inst. for Petroleum and Energy Research)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Engineering
- Publication Date
- May 1995
- Document Type
- Journal Paper
- 129 - 136
- 1995. Society of Petroleum Engineers
- 3 in the last 30 days
- 456 since 2007
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The technology of applying a polymer gel treatment before or after a polymerflood has the potential of preventing early breakthrough of polymer in highlyheterogeneous reservoirs thereby improving sweep efficiency and increasing oilrecovery. This paper presents simulation results on using polymer geltreatments to increase incremental oil recovery over that of polymer floodingin reservoirs with different degrees of crossflow and on the effect of layerpermeability contrast on the effectiveness of polymer gel treatments in polymerfloods and waterfloods. A three-dimensional, three-phase permeabilitymodification simulator was used in all studies. The reservoir model consideredis a two-layer model with layer permeability contrast varying from 0.0033 to0.5, horizontal permeability varying from 10 to 4,000 mD, and ratio of verticalpermeability to horizontal permeability varying from 0.001 to 0.1.
The results show that near-wellbore gel treatment in a polymer flood waseffective in increasing incremental oil recovery over that of a polymer floodin reservoirs with low crossflow where near-wellbore gel treatment in awaterflood was effective in increasing incremental oil recovery overwaterflood. Incremental oil recovery from a combined near-wellbore geltreatment and polymer flood was approximately equal to the sum of theincremental oil recovery from a near-wellbore gel treatment and that from apolymer flood. Because of a reduction in the permeability of thelow-permeability layer, which resulted from the crossflow of the polymer gelsystem from the high-permeability layer to the low-permeability layer duringthe placement of the large volume polymer gel system, deep polymer gelplacement was not as effective as near-wellbore gel treatment in a polymerflood in increasing incremental oil recovery over that of a polymer flood.
In reservoirs with high crossflow, where gel treatment was not effective inincreasing incremental oil recovery over waterflood, a near-wellbore geltreatment or deep gel placement in a polymer flood was also not effective inincreasing incremental oil recovery over that of a polymer flood.
Similar to the cases of waterfloods with and without gel treatment,fractional oil recoveries from a combined gel treatment and polymer flood andfrom a polymer flood were also a function of the ratio of the permeabilities ofthe two layers, but were independent of the absolute permeability in eachlayer. Polymer gel treatment in waterflooding or polymer flooding was mosteffective in increasing incremental oil recovery in reservoirs with lowcrossflow and with a layer permeability contrast in the range of about0.05.
Permeability modification is one way to improve sweep efficiency andincrease oil recovery in reservoirs that have severe layer permeabilitycontrast. This technique has been used in injection and production wells. Ininjection wells, it is used to block high-permeability or watered-out thiefzones, thereby diverting most of the injected fluids into previously unsweptzones with higher oil saturation and lesser permeability. In production wells,it is intended to reduce water production without adversely affecting oilproduction. Many polymer/crosslinker systems have been developed for thispurpose. Some of them have been successfully used in many waterfloodingprojects by independent oil producers and major oil companies but have seldombeen used in polymer flooding projects. In this work, those gel systems usingalternate slugs of polymer and completing metal solutions such as aluminumcitrate to build a polymer gel network were not considered.
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