Development Of Relative Permeability Modifiers

Daqing Oilfield is a heterogeneous sandstone reservoir of continental origin with multi-layers, and water flood is important method to guarantee stable high oil production. But, as time goes on, great amounts of injected water flows along the high permeable zone, which results in early watered-out producers and declining yield. By the end of 2002, the overall water cut for the oilfield is up to 87%, and water cut for the main pay zone has reached 90~95%. On one hand, this leads to increasing cost, superabundant water production, and possible damage for the formation structure. What's more, water in producer will also add the density of the liquid, increase the bottom hole pressure, and cause interference between layers; additionally, it can erode the downhole tools. On the other hand, water trapped dead oil zone forms in the low watered out position, and the injected water bypasses here, which leads to lower recovery.At present, the conventional water plugging technology is chemical water shutoff, which reacts on the surface or in the formation to produce water insoluble matter to plug the hole, thus prevents water producing. Water shutoff is paid great attention in domestic and overseas because effective water shutoff can keep high drive energy and ensure the effect of enhanced oil recovery (abbr. EOR). Water shutoff is regarded as pretreatment before EOR overseas, while China treats it as main method for water control and stable oil production. But the conventional water shutoff technology not only blocks the water channel, but also oil passage, thus decreases the oil production, and affects the economic effect.Relative permeability modifiers (abbr. RPM) is a kind of selective water plugging agent, namely it only decreases the permeability of water phase, causes little or even no impact on oil phase. The research on RPM can trace back to 1970s, and water-soluble polyacrylamide to reduce the water production and control the fluidity. Later on, it was found that many kinds of water-soluble polymer had the ability of disproportionate permeability reduction (abbr. DPR), meanwhile, it was also discovered that some metallic ion crosslinked polymer could get better DPR.The background of the article is the Development of Relative permeability modifiers, which is undertaken by the author and is the sub-project of Daqing Oilfield Company Ltd. project----Research on Thick Layer Fracturing and Water Controlling Technique. The target of the research is to develop modifier that is suitable for Daqing oilfield geological conditions according to the characteristic of main pay zones----thick layers. Further more, the target of water-shutoff instead of oil-shutoff can be achieved by combining other techniques such as fracturing and water injection. After a serious of research work, a kind of chromium-cross-linking phase permeability modifier system, which is mainly consist of polyacrylamide, acetic acid chromium cross linking agent, stabilizer, and bridging agent, was developed. The polymer density ranges from 1000mg/l to 6000mg/l. The temperature of the system is around 45℃. The salinity is lower than 10000mg/l; the PH value is about 7. All the features is helpful for forming a good intensity colloid. The Lab core experiment indicated that core permeability decreased and irreducible water saturation increased after injecting modifier. The phase permeability curve features special lower permeability. The injection pressure after modifier injection was obviously higher than that of before modifier injection. In addition, the injection pressure increased with the water saturation. This indicated that modifier resists water more than resists oil. The water cut of core, when compared with that before modifier injection, decreased. Oil phase permeability increased, while water phase permeability decreased obviously. Residual resistance factor was more than 2.268. Oil saturation decreased more than 10% and decreased up to 18.8%. The recovery ratio, on the other hand, increased 15.25% more than that of water...