Preformed particle gel (PPG) has been successfully synthesized and applied to control excess water production in most of the mature, waterflooded oil fields in China. This paper reports on laboratory experiments carried out to investigate PPG transport mechanisms through porous media. Visual observations in etchedglass micromodels demonstrate that PPG propagation through porous media exhibits six patterns of behavior: direct pass, adsorption, deform and pass, snap-off and pass, shrink and pass, and trap. At the macroscopic scale, PPG propagation through porous media can be described by three patterns: pass, broken and pass, and plug. The dominant pattern is determined by the pressure change with time along a tested core (as measured at specific points), the particle-size ratio of injected and produced particles from the core outlet, and the residual resistance factor of each segment along the core. Measurements from micromodel and routine coreflooding experiments show that a swollen PPG particle can pass through a pore throat with a diameter that is smaller than the particle diameter owing to the elasticity and deformability of the swollen PPG particle. The largest diameter ratio of a PPG particle and a pore throat that the PPG particle can pass through depends on the swollen PPG strength. PPG particles can pass through porous media only if the driving pressure gradient is higher than the threshold pressure gradient. The threshold pressure depends on the strength of the swollen PPG and the ratio of the particle diameter and the average pore diameter.
Gel treatment is a cost-effective method for oilfield conformance control. Traditionally, in-situ gels formed by the reaction of polymer and crosslinker at reservoirs have been used widely to control conformance. However, a newer trend is to apply preformed particle gels (PPGs) for this purpose because they are formed at surface facilities before injection and they overcome some distinct drawbacks inherent in in-situ gelation systems, such as lack of control over the gelation time, gelling uncertainty due to shear degradation, chromatographic fractionation or change of gelant compositions, and dilution by formation water. PPGs are characterized as having robust gel chemistries and as being highly insensitive to petroleum reservoir environments and interferences. They can resist temperatures up to 120 °C (250 °F) and are compatible with any kind of formation water. In this paper, we describe and discuss our extensive laboratory and field experiences with the widely applied and successful PPG technology. Highlights of illustrative PPG field applications and results are presented. An overview of what over a decade of experience in applying the PPG technology has taught us is discussed. This includes a discussion of classifying and distinguishing conformance problems and treatments, attributes of good candidate wells, requirements that must be met in candidate wells, gel treatment elements that must be implemented successfully to achieve success, and the guidelines as to where PPG conformance treatments are applied most successfully.
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