1887

Abstract

Summary

Gelation time is among the most important parameters for screening gel formulations. For deep-diversion, a complex and prohibitive setup (that includes long core samples and multiple pressure tabs) would be needed to simulate in-situ gelation. Therefore, the industry typically resorts to bulk tests. In this paper, we present a novel and convenient method to determine in-situ gelation times that capture the gellant flow and interactions within the porous medium at reservoir conditions.

We conduct a systematic study of gelation-time using an organically crosslinked polymer gel system. Both bulk and in-situ gelation tests were performed. Bulk tests included conventional bottle tests as well as rheological and NMR measurements. Our novel procedure was used for in-situ tests. A conventional composite core-sample is used. The middle core-plug is saturated with the gellant solution. Both inlet and outlet core-plugs are saturated with the polymer solution. A small predetermined amount of the same solution is injected alternatingly from the inlet and outlet ends (i.e. repeated cycles of isochoric forward and backward injections) where pressure-drops are monitored.

Results demonstrated that in-situ gelation time can be conveniently determined by our new measurement method. By monitoring the pressure-drop buildup in-situ gelation time is determined as the point where a dramatic increase is observed (i.e. a shift from slow to rapid increase in pressure-drops). For the studied system, this was determined to occur at 74 hr. Bulk gelation-time observed in bottle tests was 72 hr and hence, surprisingly, corresponded extremely well to this in-situ gelation-time estimate. Yet, we believe this direct correlation to be non-unique and possibly dependent on the gellant/rock combination. Nonetheless, we do embrace simple bottle tests as a valuable technique for initial rough gelation assessment and screening of gellant formulations. On the other hand, more elaborate bulk tests based on rheological and NMR measurements, yielded much shorter gelation-time estimates (58 and 28 hrs, respectively). This is possibly due to such measurements being more sensible to the smallest changes in gellant molecular structures that do not correspond directly to the buildup of significant flow resistance. This study provides an efficient technique for gel formulation screening and evaluation. In situ gelation behavior can be evaluated by this new technique using a conventional coreflooding setup. The technique provides a representative and cost-effective measurement method. The unique fluid injection strategy diminishes viscous fingering and keeps the integrity of gel in core, therefore, it better simulates actual gel flow in reservoir.

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/content/papers/10.3997/2214-4609.201900165
2019-04-08
2024-03-29
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