Preformed Particle Gel for Conformance Control: Factors Affecting Its Properties and Applications
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 strengthand sizecontrolled, 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.
Case Study on Prefromed Particle Gel for In-Depth Fluid Diversion
The paper describes preformed particle gel (PPG) treatments for in-depth fluid diversion in four injection wells located in the north of Lamadian, Daqing oilfield, China. Lamadian is sandstone oilfield with thick net zones. The selected four injectors have 46 connected producers with average water cut of 95.4% before treatment. The paper reports the detailed information for the four well treatments, including well candidate selection criteria, PPG treatment optimization, real-time monitoring result during PPG injection and reservoir performance after treatment. In addition, a discussion is made to analyze why so large amount of large particles can be injected into the reservoir. Large volume of PPG suspension with concentrations of 2,000-2,500 mg/L and particle sizes of 0.06-3.0 mm was injected into each well and it took about 4 months to finish each injection. The injection volume ranges from 11,458 to 17,625 m per well with a total of 56,269 m of PPG suspension (295,680 lbs of dried PPG) for the four wells. During PPG injection, the increase of the wellhead pressure was quite stable and no PPG was produced from adjacent producers. Recorded real-time monitoring Data about injection pressure and rate, PPG particle size change during PPG injection provide invaluable information to analysis the possibility of fracture/channel in the reservoir. The treatments resulted in an oil increase of 34.8 t/d and average water cut decrease of 0.94% within 10 months after treatments. Introduction Excess water production has become a major problem for oilfeld operators as more and more reservoirs mature due to long term of water flooding. Higher levels of water production result in increased levels of corrosion and scale, increased load on fluid-handling facilities, increased environmental concerns, and eventually well shut-in. Consequently, producing zones are often abandoned in an attempt to avoid water contact, even when the intervals still maitain large volumes of remaining hydrocarbons. Controlling water production has become more and more important to the oil industry. Reservoir heterogeneity is the single most important reason for low oil recovery and early excess water production. Most oilfields in China, which were discovered in continental sedimentary basins, are characterized by complex geological conditions and high permeability contrast inside reservoirs. To maintain reservoir pressure, these reservoirs were developed by water flooding from early stage of their development. Many of them have been hydraulically fractured, intentionally or unintentionally, or have been channeled due to mineral dissolution and production during waterflooding (Liu, 2006). Reservoirs with induced fractures or high-permeability channels are quite common in the mature oilfields. Gel treatment is a cost-effective method to improve sweep efficiency in reservoirs and to reduce excess water production during oil and gas production. Traditionally, gels are usually placed near wellbore of production or injection wells to correct inter-layer heterogeneity or heal fracture. However, the remaining oil on the top of a thick heterogeneous layer has become the most important target to improve oil recovery as a reservoir matures. In-depth diversion gels (Seright, 2004, Frampton, 2004, Sydansk, 2004, 2005, Cheung, 2007, Rousseau, 2005, Bai, 2007) have been reported to penetrate deeply into higher permeability zones or fractures and seal or partially seal them off thus creating high flow resistance in former, watered-out, high permeability portion of the zones. When successful, these gel systems divert a portion of the injection water into areas not previously swept by water shown in Fig. 1. Traditionally in-situ gels have been widely used to control conformance. The mixture of polymer and crosslinker called gelant is injected into target formation and react to form gel to fully or partially seal the formation at reservoir temperature (Sydansk, 1992, Jain, 2005). So the gelation occurs in reservoir conditions. A new trend in gel treatments is applying preformed gels for the purpose because the preformed gels are formed at surface facilities before injection and no gelation occurs in reservoirs so they can overcome some distinct drawbacks inherent in in-situ gelation systems, such as lack of
The role of prolactin in andrology: what is new?
Prolactin (PRL) has been long deemed as a hormone involved only in female reproduction. However, PRL is a surprising hormone and, since its identification in the 1970s, its attributed functions have greatly increased. However, its specific role in male health is still widely unknown. Recently, low PRL has been associated with reduced ejaculate and seminal vesicle volume in infertile subjects. In addition, in men consulting for sexual dysfunction, hypoprolactinemia has been associated with erectile dysfunction and premature ejaculation, findings further confirmed in the general European population and infertile men. Several metabolic derangements, recapitulating metabolic syndrome, have also been associated with low PRL both in men with sexual dysfunction and from the general European population. In men with sexual dysfunction, followed-up for more than 4 years, low PRL was identified as an independent predictor of the incidence of major adverse cardiovascular events. Finally, an association with anxiety or depressive symptoms has been found in men with sexual dysfunction and from the general European population. While a direct role for impaired PRL function in the pathogenesis of these reproductive, sexual, metabolic and psychological disorders is conceivable, the possibility that low PRL is a mirror of an increased dopaminergic or a decreased serotonergic tone cannot be ruled-out. Hyperactivity of the dopaminergic system can explain only a few of the aforementioned findings, whereas a hypo-serotonergic tone fits well with the clinical features associated with low PRL, and there is significant evidence supporting the hypothesis that PRL could be a mirror of serotonin in the brain.