Preformed Particle Gel for Conformance Control: Factors Affecting Its Properties and Applications
- Baojun Bai (U. of Missouri Rolla) | Liangxiong Li (New Mexico Tech) | Yuzhang Liu (PetroChina Co. Ltd.) | He Liu (Daqing Petroleum Co.) | Zhongguo Wang (Daqing Petroleum Co.) | Chunmei You (Daqing Petroleum Co.)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Evaluation & Engineering
- Publication Date
- August 2007
- Document Type
- Journal Paper
- 415 - 422
- 2007. Society of Petroleum Engineers
- 3.2.5 Produced Sand / Solids Management and Control, 5.4.1 Waterflooding, 6.5.2 Water use, produced water discharge and disposal, 5.6.4 Drillstem/Well Testing, 4.3.4 Scale, 3.2.6 Produced Water Management, 4.1.2 Separation and Treating, 4.1.5 Processing Equipment, 5.6.5 Tracers, 5.8.6 Naturally Fractured Reservoir, 2.5.2 Fracturing Materials (Fluids, Proppant), 5.4 Enhanced Recovery, 5.1.1 Exploration, Development, Structural Geology, 2.4.3 Sand/Solids Control, 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 1.10 Drilling Equipment, 5.2 Reservoir Fluid Dynamics, 2.2.2 Perforating, 3 Production and Well Operations, 4.6 Natural Gas
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Preformed particle gel (PPG) is a particled superabsorbent crossklinking polymer that can swell up to 200 times its orginal size in brine. The use of PPG as a fluid-diverting agent to control conformance is a novel process designed to overcome some distinct drawbacks inherent in in-situ gelation systems. This paper introduces the effect of gelant compositions and reservoir environments on the two properties of PPG: swollen gel strength and swelling capacity. Results have shown that PPG properties are influenced by gelant compositions, temperature, brine salinity, and pH below 6. Temperature increases PPG swelling capacity but decreases its swollen gel strength. Salinity decreases PPG swelling capacity but increases its swollen gel strength. PPG is thermostable at an elevated temperature of 120°C if a special additive agent is added into its gelant as a composition. PPG is strength- and size-controlled, environmentally friendly, and not sensitive to reservoir minerals and formation water salinity.
Two field applications are introduced to illustrate the criteria of well candidate selection and the design and operation process of PPG treatments. Field applications show that PPG treatment is a cost-effective method to correct permeability heterogeneity for the reservoirs with fractures or channels, both of which are widely found in mature waterflooded oil fields.
Most oil fields in China are found in continental sedimentary basins. They are characterized by complex geologic conditions and high permeability contrast inside reservoirs. To maintain or increase the driving force, these oil fields were developed by waterflooding. However, serious vertical and lateral formation heterogeneity has resulted in the rapid water-cut increase of production wells. Moreover, sand production and rock mineral dissolution due to water injection have made reservoirs much more heterogenerous. Many interwell tracer tests have shown that channels or fractures widely exist in most oil fields, whether they have fractures or not during their early development stage. Another demonstration of worsening heterogeneity comes from the clay gel treatments for conformance control in China oil fields. Many injection wells have successfully injected tens or hundreds of tons of clay. If we calculate the permeability from Darcy law according to the "1/9-1/3?? rule (Maroudas 1966; Pautz et al. 1989), which gives the relationship of particle penetration depth into porous media to the ratio of pore-throat diameter and particle size, the formation permeability should be more than 1,000 darcies (Bai 2001). Moreover, early polymer breakthroughs in the Daqing, Nanyan, and Shengli oil fields have further demonstrated that channels or fractures are common in most oil fields (Bai 2001). Severe reservoir heterogeneity has become one of the most urgent problems that reservoir engineers have to solve.
To control water cut and improve the oil recovery of oil fields, many technologies, such as polymer flooding, surfactant flooding, foam flooding, and so on, have been widely applied in China in past decades (Wang et al. 2003; Yang et al. 1988, 2003; Song et al. 1995). One of the most popular methods is to inject gels to reduce the flow capacity of channels or fractures and divert the following fluid (normally, water) to unswept oil zones (Bai et al. 1999; Seright et al. 2001). Before the 1990s, gel treatments focused on correcting permeability heterogeneity near the wellbore (normally 5 to 10 m). However, in-depth gel treatments have become more important within the last 10 years because the crossflow in a heterogeneous thick zone has become a significant factor influencing the oil recovery of mature oil fields; in addition, many wells have been treated multiple times using gels, resulting in no more oil remaining near a wellbore (Liu 1995).
Recently, several authors have recommended using preformed gel to control conformance in mature oil fields (Seright et al. 2001; Seright 2000; Chauveteau et al. 2000, 2001; Feng et al. 2003; Li et al. 1999; Coste et al. 2000; Bai et al. 2007) because it can overcome some distinct drawbacks inherent in in-situ gelation systems, such as difficulty of gelation time control, potential damage of low-permeability hydrocarbon zones, and the uncertain nature of gelling caused by the shear in surface facilities and porous media. Seright et al. (2001) and Seright (2000) studied some properties of preformed bulk gel through fractures and stated that preformed gel had better placement than in-situ gel and could effectively reduce gel damage on low-permeability unswept oil zones. Chauveteau et al. (2000, 2001) synthesized preformed microgels that were crosslinked under shear. Feng et al. (2003) demonstrated that the microgels could be injected easily into porous media without any sign of plugging and showed that these microgels could be good candidates for water-shutoff and profile-control operations.
On the basis of the reservoir status of the China oil fields discussed above, a new idea using PPG to control conformance was proposed by Li et al.(1999) in China. Coste et al. (2000) and Bai et al. (2007) analyzed some properties of PPG and PPG propagation mechanisms through porous media.
In this paper, the effects of gel compositions and reservoir conditions on PPG properties were systematically studied by evaluating swollen PPG strength and PPG swelling capacity. Two of the earliest field application cases were introduced to show how to screen candidate wells and how to operate the injection procedures.
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