No abstract

While synthetic polymer floods are being deployed in mild temperature and low salinity fields, many oilfields (harsh conditions) remain inaccessible due to performance limitations, and concentration requirements, which adversely affect project economics. Historically, biopolymers have been considered in such reservoirs, with mixed results. Xanthan was used in the 1980's, while more recently schizophyllan polymer was tested in a pilot study. This study presents scleroglucan polymers as a class of viscosifiers that demonstrate excellent performance in harsh temperature and salinity reservoirs. Scleroglucan polymers do not suffer from catastrophic drop in viscosity in the presence of high concentration of divalent ions. This makes produced water re-injection projects without water treatment a reality. This work demonstrates that cost-effective, high purity EOR grade Scleroglucan polymers, show excellent performance in lab trials as related to excellent rheological properties, injectivity, bio and thermal stability and with minimal shear degradation. Injectivity tests demonstrated good propagation through cores without blockage or injectivity issues. Resistance factors and residual resistance factors are in the desirable range. Core floods carried out in sandstone and carbonate outcrop cores demonstrated that adsorption values and oil recoveries are consistently in the expected range for polymer recoveries. Shear degradation studies showed that recycling scleroglucan through a centrifugal pump causes less than 5% drop in viscosity after 100 passes while synthetic polymer showed substantial loss after a single pass and a 50% drop after 10 passes through the same pump. Capillary shear testing (API RP 63 method) of scleroglucan shows little change in viscosity upon multiple passes through shear regimes greater than 150,000 s−1. Scleroglucan polymer solution showed less than 25% drop in viscosity after exposure to 115 °C for six months. No change in viscosity was observed at 95 °C after one year. Scleroglucan has no compatibility issues through 6 months (at 37, 85, and 95 °C) with glutaraldehyde and tributyl tetradecyl phosphonium chloride (TTPC) biocides. Long term biostability studies at various temperatures and salinities are ongoing - current data will be presented. Scleroglucan has excellent stability in the presence of hydrogen sulfide (H2S) and ferrous species (Fe2+) under fully aerobic conditions! This work provides insight on the potential of using EOR grade scleroglucan for CEOR in harsh condition reservoirs. Currently, the program is moving towards pilot implementation of a scleroglucan formulation to demonstrate large scale hydration, long term injectivity and oil recovery.

Polymers for enhanced oil recovery (EOR) purposes are required to have long term mechanical, thermal, chemical, and biological stability across a wide variety of conditions throughout field deployment. In this work we expand upon initial studies of scleroglucan biopolymer stability and demonstrate that scleroglucan solutions retain a significant proportion of their initial viscosity over a large range of stresses. Thermal stability of the biopolymer, scleroglucan, was tested at temperatures of up to 115°C, wherein the samples retained >95 % of the original viscosity over several months, and at 105 °C sclergolucan maintained >95 % viscosity over the course of 720 days. Scleroglucan was found to be chemically compatible with formaldehyde, glutaraldehyde, tetrakis(hydroxymethyl)-phosphonium sulfate (THPS), and 1,3,4,6-tetrakis(hydroxymethyl)tetrahydroimidazo-[4,5-d]imidazole-2,5(1H,3H)-dione (TMAD) for six months at 37 °C, 85 °C, and 95 °C, indicating these biocides have the potential for use in microbial control during scleroglucan implementation under various conditions. Rheological studies indicate the viscosifying power of scleroglucan is largely unimpacted by common reservoir salts (including divalents and trivalents) even through 20 % (wt/wt) salt addition. Microbial risks to polymer stability were also investigated. The susceptibility of scleroglucan to microbial degradation was assessed under reservoir relevant conditions using a bottle test system in which the polymer was incubated with active microbial cultures under various conditions that simulate reservoirs spanning 3.5 % to 17 % salinity and 30 °C to 90 °C. Our tests of microbial degradation found that anaerobic samples incubated with active microbial consortia under lower salinities and temperature lost viscosity with concomitant microbial growth indicating the presence of scleroglucan degrading organisms in the inoculum. However, anaerobic samples at temperatures above 60 °C and salinities greater than 7 % retained viscosity during the experiment illustrating polymer stability under conditions similar to those of harsh reservoirs. This study further refines the window of operation where scleroglucan maintains functional viscosity and may be employed for EOR use.

Effective and economic recovery of oil from fractured reservoirs by steamflooding rely on thorough understanding of the physical process mechanisms. The objective of this research is to study steamflooding mechanisms in fractured porous media using laboratory experiments and mathematical modeling. The experimental results have been published previously [1-3]. A mathematical model developed for simulating laboratory coreflood results is presented in this paper. The model is a two-dimensional, three phase, thermal simulator which includes the effects of gravity, capillarity and thermal swelling. Thermal effects on capillary pressure and relative permeabilities are included. Simulation and analysis of laboratory experiments are presented. Sensitivity studies demonstrate the effects of injection rate, pressure and temperature, fracture aperture, capillary pressure, and relative and absolute permeabilities on oil production.

Aspen wood chip samples were subjected to hot water treatments (autohydrolysis) with and without sulfuric acid to extract hemicelluloses. A liquor-to-wood ratio of 4:1 was used at temperatures from 130° to 210°C and H2SO4 concentrations in the range from 0% to 1% (w/v), with treatment times up to 4.5 h. Researchers analyzed wood residues and their corresponding hydrolysates, and determined the most suitable conditions for the extraction. Additional information on the suitability of wood residues for pulping purposes is also considered.