USE OF POLYMERS TO RECOVER VISCOUS OIL FROM UNCONVENTIONAL RESERVOIRS

This final technical progress report summarizes work performed the project, 'Use of Polymers to Recover Viscous Oil from Unconventional Reservoirs.' The objective of this three-year research project was to develop methods using water soluble polymers to recover viscous oil from unconventional reservoirs (i.e., on Alaska's North Slope). The project had three technical tasks. First, limits were re-examined and redefined for where polymer flooding technology can be applied with respect to unfavorable displacements. Second, we tested existing and new polymers for effective polymer flooding of viscous oil, and we tested newly proposed mechanisms for oil displacement by polymer solutions. Third, we examined novel methods of using polymer gels to improve sweep efficiency during recovery of unconventional viscous oil. This report details work performed during the project. First, using fractional flow calculations, we examined the potential of polymer flooding for recovering viscous oils when the polymer is able to reduce the residual oil saturation to a value less than that of a waterflood. Second, we extensively investigated the rheology in porous media for a new hydrophobic associative polymer. Third, using simulation and analytical studies, we compared oil recovery efficiency for polymer flooding versus in-depth profile modification (i.e., 'Bright Water') as a function of (1) permeability contrast, (2) relative zone thickness, (3) oil viscosity, (4) polymer solution viscosity, (5) polymer or blocking-agent bank size, and (6) relative costs for polymer versus blocking agent. Fourth, we experimentally established how much polymer flooding can reduce the residual oil saturation in an oil-wet core that is saturated with viscous North Slope crude. Finally, an experimental study compared mechanical degradation of an associative polymer with that of a partially hydrolyzed polyacrylamide. Detailed results from the first two years of the project may be found in our first and second annual reports. Our latest research results, along with detailed documentation of our past work, can be found on our web site at http://baervan.nmt.edu/randy/. As an overall summary of important findings for the project, polymer flooding has tremendous potential for enhanced recovery of viscous oil. Fear of substantial injectivity reduction was a primary hurdle that limited application of polymer flooding. However, that concern is largely mitigated by (1) use of horizontal wells and (2) judicious injection above the formation parting pressure. Field cases now exist where 200-300-cp polymer solutions are injected without significant reductions in injectivity. Concern about costs associated with injection of viscous polymer solutions was a second major hurdle. However, that concern is reduced substantially by realization that polymer viscosity increases approximately with the square of polymer concentration. Viscosity can be doubled with only a 40% increase in polymer concentration. Up to a readily definable point, increases in viscosity of the injected polymer solution are directly related to increases in sweep efficiency and oil recovery. Previously published simulation results - suggesting that shear-thinning polymer solutions were detrimental to sweep efficiency - were shown to be unfounded (both theoretically and experimentally)

Clinical Decision Making of Rural Novice Nurses

The purpose of this study was to develop substantive theory regarding decision making by the novice nurse in a rural hospital setting. Interviews were guided by the following research questions: What cues were used by novice rural registered nurses in order to make clinical decisions? What were the sources of feedback which influenced subsequent decision making for processing of cues? Theory development was based on an in-depth investigation of 12 novice nurses practicing in rural critical access hospitals in a North Central State. This study consisted of face to face interviews with 12 registered nurses, nine of whom were observed during their work day. Eleven of the 12 participants were interviewed a second time, during which they reviewed their transcripts and the emerging themes and categories as a method of member checking. Directors of nursing from the research sites and rural hospitals not involved in the study, experienced researchers, and nurse educators facilitated triangulation of the findings. This study revealed novice nurses were able to identify varying cues for decision making, including patient vital signs and patient assessments. These cues were often compared to the nurses\u27 previous encounters with the patients through the health care system or through contact in the community. Familiarity with a diagnosis, such as chest pain, was explained by participants as knowledge they had gained during formal education and in patient encounters within their first year of practice. Where cues were more subtle, participants turned to coworkers to confirm or deny their hunches and to help them decide on actions. They did not, as has been suggested in the literature, turn back to textbooks or linear decision making models to help them analyze the situations. Recommendations were made for nurse educators, who have been tasked with facilitating critical thinking in all nursing students in the preparation of the graduate generalist practitioner. Researchers have been provided suggestions for future exploration of decision making processes in rural nursing. Those who practice rural nursing in either leadership or supportive work roles were given recommendations related to mentoring the new nurse while fostering decision making skills

A Review of Polymer Gel Utilization in Carbon Dioxide Flow Control at the Core and Field Scale

Polymer gel has been used for water conformance control for several decades and may have significant potential in remediating unfavorable carbon dioxide (CO2) flow in the subsurface. High-mobility CO2 may channel quickly through sedimentary reservoirs, where unfavorable displacements are worsened in the presence of heterogeneities. Flow diversion technology targeting and withstanding CO2 is therefore essential to improving sweep efficiency and increasing storage potential. Polymer gel treatments have been demonstrated to remediate CO2 channeling in several enhanced oil recovery (EOR) field applications and have been proposed as a means to remediate wellbore and seal leakage during carbon sequestration. The goal of this review is to assess CO2 conformance control by polymer gel in published laboratory work related to both storage and EOR operations. Although field implementation of polymer gel has been successful in reducing CO2 flow, supporting experimental work on the laboratory scale is scattered, with both results and parameters varied. This paper summarizes the available literature and proposes a framework for future experimental work to aid more systematic assessment.publishedVersio

Improved techniques for fluid diversion in oil recovery. Final report

This three-year project had two technical objectives. The first objective was to compare the effectiveness of gels in fluid diversion (water shutoff) with those of other types of processes. Several different types of fluid-diversion processes were compared, including those using gels, foams, emulsions, particulates, and microorganisms. The ultimate goals of these comparisons were to (1) establish which of these processes are most effective in a given application and (2) determine whether aspects of one process can be combined with those of other processes to improve performance. Analyses and experiments were performed to verify which materials are the most effective in entering and blocking high-permeability zones. The second objective of the project was to identify the mechanisms by which materials (particularly gels) selectively reduce permeability to water more than to oil. A capacity to reduce water permeability much more than oil or gas permeability is critical to the success of gel treatments in production wells if zones cannot be isolated during gel placement. Topics covered in this report include (1) determination of gel properties in fractures, (2) investigation of schemes to optimize gel placement in fractured systems, (3) an investigation of why some polymers and gels can reduce water permeability more than oil permeability, (4) consideration of whether microorganisms and particulates can exhibit placement properties that are superior to those of gels, and (5) examination of when foams may show placement properties that are superior to those of gels

Aperture-Tolerant, Chemical-Based Methods to Reduce Channeling

This final technical progress report describes work performed from October 1, 2004, through May 16, 2007, for the project, 'Aperture-Tolerant, Chemical-Based Methods to Reduce Channeling'. We explored the potential of pore-filling gels for reducing excess water production from both fractured and unfractured production wells. Several gel formulations were identified that met the requirements--i.e., providing water residual resistance factors greater than 2,000 and ultimate oil residual resistance factors (F{sub rro}) of 2 or less. Significant oil throughput was required to achieve low F{sub rro} values, suggesting that gelant penetration into porous rock must be small (a few feet or less) for existing pore-filling gels to provide effective disproportionate permeability reduction. Compared with adsorbed polymers and weak gels, strong pore-filling gels can provide greater reliability and behavior that is insensitive to the initial rock permeability. Guidance is provided on where relative-permeability-modification/disproportionate-permeability-reduction treatments can be successfully applied for use in either oil or gas production wells. When properly designed and executed, these treatments can be successfully applied to a limited range of oilfield excessive-water-production problems. We examined whether gel rheology can explain behavior during extrusion through fractures. The rheology behavior of the gels tested showed a strong parallel to the results obtained from previous gel extrusion experiments. However, for a given aperture (fracture width or plate-plate separation), the pressure gradients measured during the gel extrusion experiments were much higher than anticipated from rheology measurements. Extensive experiments established that wall slip and first normal stress difference were not responsible for the pressure gradient discrepancy. To explain the discrepancy, we noted that the aperture for gel flow (for mobile gel wormholing through concentrated immobile gel within the fracture) was much narrower than the width of the fracture. The potential of various approaches were investigated for improving sweep in parts of the Daqing Oil Field that have been EOR targets. Possibilities included (1) gel treatments that are directed at channeling through fractures, (2) colloidal dispersion gels, (3) reduced polymer degradation, (4) more viscous polymer solutions, and (5) foams and other methods. Fractures were present in a number of Daqing wells (both injectors and producers). Because the fractures were narrow far from the wellbore, severe channeling did not occur. On the contrary, fractures near the wellbore aided reservoir sweep. In the February 2006 issue of the Journal of Petroleum Technology, a 'Distinguished-Author-Series' paper claimed that a process using aqueous colloidal dispersion gels (CDG gels) performed superior to polymer flooding. Unfortunately, this claim is misleading and generally incorrect. Colloidal dispersion gels, in their present state of technological development, should not be advocated as an improvement to, or substitute for, polymer flooding

A study comparing student achievement in a full-service school and a non-full-service school.

Student achievement indicators in the two schools were compared. The schools were similar in enrollment, community type, percent low-income students, and percent minority students. Data gathered from the schools was retrieved from each school's State Department of Education website report card database.A t-test was used to compare data between the schools. A difference was significant when p< 0.05. In all the areas tested, the null hypothesis was rejected. The null hypothesis was rejected due to a significant difference in academic achievement between the two schools understudy. The differences in student achievement indicators were explained primarily as differences in the characteristics of student groups in the two schools. An implication of the study is that implementation of the full-service school model does not necessarily contribute to improved student achievement.The purpose of this study was to examine differences in student achievement indicators in a full-service school and at a demographically similar, non-full-service school. A full-service school integrates the delivery of quality educational services with needed health and social services. Evaluation of student learning outcomes in full-service schools is important to policy level support for coordination of services for children.The student achievement indicators compared were proficiency levels attained on the individual state's proficiency exams in the areas of English (Reading) over a four-year period for tenth grade students, and a three-year period for all ninth grade students in the area of Algebra I. Additionally, dropout rates and graduation rates were compared over a four-year period. These were considered achievement related factors

Conformance Improvement Using Gels

This technical progress report describes work performed from September 1, 2003, through February 29, 2004, for the project, ''Conformance Improvement Using Gels.'' We examined the properties of several ''partially formed'' gels that were formulated with a combination of high and low molecular weight HPAM polymers. After placement in 4-mm-wide fractures, these gels required about 25 psi/ft for brine to breach the gel (the best performance to date in fractures this wide). After this breach, stabilized residual resistance factors decreased significantly with increased flow rate. Also, residual resistance factors were up to 9 times greater for water than for oil. Nevertheless, permeability reduction factors were substantial for both water and oil flow. Gel with 2.5% chopped fiberglass effectively plugged 4-mm-wide fractures if a 0.5-mm-wide constriction was present. The ability to screen-out at a constriction appears crucial for particulate incorporation to be useful in plugging fractures. In addition to fiberglass, we examined incorporation of polypropylene fibers into gels. Once dispersed in brine or gelant, the polypropylene fibers exhibited the least gravity segregation of any particulate that we have tested to date. In fractures with widths of at least 2 mm, 24-hr-old gels (0.5% high molecular weight HPAM) with 0.5% fiber did not exhibit progressive plugging during placement and showed extrusion pressure gradients similar to those of gels without the fiber. The presence of the fiber roughly doubled the gel's resistance to first breach by brine flow. The breaching pressure gradients were not as large as for gels made with high and low molecular weight polymers (mentioned above). However, their material requirements and costs (i.e., polymer and/or particulate concentrations) were substantially lower than for those gels. A partially formed gel made with 0.5% HPAM did not enter a 0.052-mm-wide fracture when applying a pressure gradient of 65 psi/ft. This result suggests a lower limit of fracture width for entry of formed or partially formed gels (when reasonable pressure gradients are applied). In unfractured porous rock, we investigated the time dependence of oil and water permeabilities during various cycles of oil and water injection after placement of a Cr(III)-acetate-HPAM gel. Permeability to water stabilized rapidly (within 1 pore volume, PV), while permeability to oil stabilized gradually over the course of 100 PV. The behavior was surprisingly insensitive to core material (strongly water-wet Berea sandstone and strongly oil-wet porous polyethylene), core permeability (740 to 10,000 md), and applied pressure gradient (10 to 100 psi/ft)

Improved Methods for Water Shutoff. Annual Report, October 1, 1996--September 30, 1997

In the US, more than 20 billion barrels of water are produced each year during oilfield operations. There is a tremendous economic incentive to reduce water production if that can be accomplished without significantly sacrificing hydrocarbon production. In an earlier project, the authors determined that the ability of blocking agents to reduce permeability to water much more than that to oil is critical to the success of these blocking treatments in production wells if zones are not protected during placement of the blocking agent. This research project has three objectives: (1) to identify chemical blocking agents that will during placement, flow readily through fractures without penetrating significantly into porous rock and without screening out or developing excessive pressure gradients and at a predictable and controllable time, become immobile and resist breakdown upon exposure to moderate to high pressure gradients; (2) to identify schemes that optimize placement of blocking agents; and (3) to explain why gels and other chemical blocking agents reduce permeability to one phase (e.g., water) more than that of another phase (e.g., oil or gas). Chapter 2 examines the validity of using water/oil ratio plots to distinguish between coning and channeling water production mechanisms. Chapter 3 develops a method to size gelant treatments in hydraulically fractured production wells. Chapter 4 identifies characteristics of naturally fractured reservoirs where gel treatments have the greatest potential. Chapter 5 reports experimental results from studies of gel properties in fractures. Finally, Chapter 6, the authors investigate the mechanism responsible for gels reducing the permeability to water more than that to oil