Field Experience With a Novel Calcium-Tolerant Fluid-Loss Additive for Drilling Muds

Abstract

Abstract A novel sulfonated polymer used as a fluid loss additive in water base drilling fluids is introduced. Major features of this 100% synthetic polymer are temperature stability up to 400 deg. F (200 deg. C), salt tolerance up to saturation, hardness tolerance to 75,000 ppm calcium ions and complete neutral effect on ppm calcium ions and complete neutral effect on viscosity. A remarkable thermal stabilizing effect on polysaccharide fluid loss reducers like e.g. starch, polysaccharide fluid loss reducers like e.g. starch, CMC, PAC, HEC, CMHEC is found. The mode of action of the novel polymer is investigated by means of SEM photos from drilling mud filter cakes. photos from drilling mud filter cakes. Field experience with the novel polymer includes such fluid systems as fresh water, sea water, salt saturated, KCl/polymer, dispersed muds and solids free brines. Field data from over 20 wells in Europe and North America both on and offshore are presented and analyzed. presented and analyzed. Field examples for the thermal stabilization effect of the novel polymer on starch are given. The novel polymer extends the thermal stability of starch from 245 polymer extends the thermal stability of starch from 245 deg. F (120 deg. C) to 295 deg. F (145 deg. C). More than a dozen German Zechstein wells have been drilled with this system to depths up to 15,750 ft (4800m), BHST to 280 deg. F (137 deg. C) and calcium contamination up to 42,000 ppm. Cellulose type polymers such as CMC, PAC, HEC and CMHEC were thermally stabilized by the novel polymer. A North German gas well using CMC for polymer. A North German gas well using CMC for filtration control added the novel polymer, reduced the HPHT filtrate from 22 ml to 12 ml and cut the daily maintenance rate of CMC by half. Offshore Norway a KCl clay-free fluid with CMHEC was extended to over 320 deg. F (160 deg. C) by addition of the novel polymer. polymer. The novel polymer significantly reduces the HPHT filtrates of dispersed systems. On an offshore Gulf of Mexico well the HPHT filtrate was reduced from 45 mls to 5.3 mls in a lignosulfonate sea water mud with 5.25 ppb of the novel polymer being added. A Central Texas well with a lignite fresh water mud required lime treatment to combat a heavy CO influx resulting in calcium contamination. The novel polymer lowered the HPHT filtrate from 35–40 to below 20 mls. In a highly deviated Mobile Bay (USA) well a combination of the novel polymer and a lignite-phenolic resin yielded temperature stability over 500 deg. F (260 deg. C) and reduced the HPHT by 80%. Introduction The drilling fluid industry today offers a variety of filtration control additives with various properties and performances. In todays situation of properties and performances. In todays situation of depressed oil prices which keeps considerable pressure on low exploration costs for the oil companies it is an important task of the drilling fluid engineer to select the technically and economically superior fluid loss control additive for any given application. Several years ago oil companies as well as drilling mud service companies indicated interest in a synthetic polymeric fluid loss control additive with high electrolyte tolerance especially towards calcium and magnesium ions and with temperature stability significantly exceeding carboxymethylcellulose (CMC). This product should be available at a reasonable and economical price. Our research and development department put together a group of chemists trying to tailor a novel type of polymer which was to meet the given specifications as close as possible. The result of this research project is a novel, synthetic and polymeric fluid loss additive. P. 351