Reseraches On Formationaqueous Damage Mechanisms Of Low Permeability Reservoirs

With the Western China South Sea Oilfield stepped into mid-late period, the pressure of reservoir characterized by medium-low permeability is declining significantly and not enough to supply natural flow, so besides various stimulation, a number of electrical submersible pump have been employed, consequently resulting in frequently pump inspection. In those operations, as a consequence of payzones featured with high clay content, compacting lithology,low permeability, high flow resistance, the imcompatibility of workover fluid with formation and heavily invasion produce vast formation damage, including water blocking, emulsification, clay swelling, resulting in the great decrease in oil production and long period of recovery time.To solve above problems, this dissertation presented evalution method and index system for worker-fluid damage by comparative analysis of the pre and post operation production data and systematic study of the basic geologic characters,lithologic features, physical properties characteristics, pore structure characteristics, the content and types of sensitive mineral of reservoirs, and eventually attained the main formation damage mechanism- water blocking. Meanwhile, water sensetivity, velocity sensitivity, inorganic scale and organic Scale were prove to be the secondary factor. Moreover, to the problem of heavy invasion and stringent environmental restriction, by dissolving test and self-designed filtration reduction experiments, HDS-2 was screened out as fluid loss additive,which can reduce filtration at least 90% with concentration less than 5%; anticlayswelling agent,KCl was located to more than 2% by clay linear expansion test; and the reasonable concentration of DY-OH3011 as the reverse wetting agent was 0.05%. Finally, allow for the various water cut of different wells and payzones, innovative experiments were implemented to evaluate the new workover fluid system, and the results showed that it prevented filtration loss greatly and return permeability rates were more than 87% irrespective of water cut. It was also evidently seen that the addition of reverse wetting agent contributed to greater high return permeability which reduced with water saturation fall.