TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractConformance polymer systems have been successfully applied for many years to control undesired water production from hydrocarbon wells. However, currently available polymer systems present a number of limitations for high-temperature conformance applications (> 300 o F). Based on laboratory research, this paper documents the results of the development and evaluation of polymer gel systems used as sealants to shut off water production in high-temperature environments. The polymer systems were evaluated by their effectiveness to: (a) provide adequate gel time for placement (up to 400 o F), (b) limit permeability to water at temperatures up to 375 o F in sandpack flow experiments, and (c) provide long-term thermal stability in sandpack flow experiments at elevated temperature (up to one-year study).A commercially available polymer system that has been successfully used in field applications (up to 275 o F) has been modified to extend its applicability up to 375 o F. Recently developed base polymer, crosslinker, and retarder were tested successfully to extend the temperature range of applicability of this polymer system. Discussed are: (1) methodology used for gelation time measurement of polymer systems at elevated temperatures, and (2) laboratory results regarding gelation time of crosslinked polymer systems when varying temperature, base polymer concentration, crosslinker concentration, retarder concentration, salinity of mixing brine, and/or pH of solution.Additionally, this paper discusses and describes the dynamic flow through porous media experiments performed to simulate high-temperature / high-pressure reservoir conditions to evaluate the performance of polymer systems at elevated temperatures (up to 375 o F). Specifically, this paper details:(1) the physical laboratory equipment and test conditions used for dynamic flow studies, (2) experimental procedure regarding short-term and long-term testing, and (3) the effect of temperature versus permeability reduction over time.
This paper presents the results of laboratory evaluation regarding the effectiveness of novel, organically crosslinked, high-temperature, conformance polymer gel systems as sealants. Effectiveness of these sealant gels is evaluated by attempting water flow through high-permeability cores under residual oil conditions. The effectiveness of the sealants toblock water permeability at temperatures up to 350°F,provide long-term sealant properties at these temperatures, andprovide adequate gel time for placement is measured. The ultimate goal is to determine whether the selected crosslinked polymer systems provide useable extended gel times and maintain thermal stability to 350°F. Discussed arethe physical laboratory model and test conditions used to perform dynamic core flow studies over extended periods in determining the impact of sealant exposure to elevated temperatures and subsequent required modifications,experimental procedure used for dynamic core flow studies,the effect of temperature on permeability reduction over time,the impact of threshold pressure (differential pressure required before fluid flow begins through a treated core) on permeability reduction over time,laboratory methodology used for gelation time measurement of a new, novel, organically crosslinked, high-temperature, conformance polymer gel system, andlaboratory results regarding gelation time of the polymer system as a function of temperature up to 350°F. Introduction Excessive water production from hydrocarbon reservoirs is one of the most serious problems in the oil industry. Remediation techniques for controlling water production, generally referred to as conformance control, include the use of polymer systems to reduce or plug permeability to water. This paper mainly discusses water control in high-temperature environments for treating hydrocarbon-producing wells to reduce water production for applications in which water and hydrocarbon zones are clearly separated. The principle of operation of this technique is to pump the polymer system into the formation around the wellbore and then propagate through the rock matrix. In-situ gelation takes place, plugging pore spaces and channels, thereby limiting undesired water flow. Then, a permanent barrier strategically placed only in the water zone is formed because the oil- and water-producing zones can be mechanically isolated. Literature Review A variety of techniques for controlling water production have been attempted by the oil industry. Earlier attempts to reduce water production included mechanical isolation, squeeze cementing, solid slurry (clay) injection, and oil/water emulsion and silicate injection. More successful results have been obtained with in-situ polymerized systems, crosslinked polymeric solutions, and silicate-based gels.1 Polymer gel systems have emerged over the last decade as one of the most effective tools for controlling water production. One of the most widely used polymer systems employs polyacrylamides (PAMs) or acrylamide co-polymer and chromium [Cr(III)] as a crosslinker.2 Cr(III) has been extensively used because of its high success rate and relatively low cost. However, the short gelation times of this system at elevated temperature limit their application to lower temperature reservoirs.3 Other problems with this system include thermal stability, unpredictable gel times, gel instability in the presence of chemical species that are potential ligands, toxicity concerns, and limited propagation into the target pore volume.4 Another polymer system widely used is a water-based gel based on phenol/formaldehyde crosslinker for homo-, co-, and ter-polymer systems containing acrylamide. The loss of phenol by partitioning into the crude oil that it contacts has been identified as an important issue for this polymer system.5 Toxicity issues associated with formaldehyde and phenol need to be overcome as well.
Summary This paper presents a comprehensive comparison of different dynamic and static approaches for assessing building performance under sequential earthquakes and tsunami. A 10‐storey reinforced concrete seismically designed Japanese vertical evacuation structure is adopted as a case study for the investigation. The case study building is first assessed under sequential earthquake and tsunami nonlinear response history analyses: the first time this is done in the literature. The resulting engineering demand parameters are then compared with those obtained when the analysis procedure is systematically simplified by substituting different static approaches for the nonlinear response history analyses in both the earthquake and tsunami loading phases. Different unloading approaches are also tested for the cases when an earthquake pushover is adopted. The results show that an earthquake nonlinear response history analysis, followed by a transient free vibration and a tsunami variable depth pushover, provides the best alternative to full dynamic analyses in terms of accuracy and computational efficiency. This structural analysis combination is recommended and has the advantage that it does not require the tsunami inundation time history to be known in advance. The proposed double pushover approach is instead deemed only suitable for the collapse assessment of regular low to mid‐rise buildings and for the development of collapse fragility functions. An important observation made is that sustained earthquake damage seems not to affect the tsunami resistance of the case study building when the fully dynamic analysis is carried out for the sequential loading. This observation will be the subject of future work.
Summary Water production becomes a major problem as hydrocarbon-producing fields mature. Higher levels of water production result in increased levels of corrosion and scale, increased load on fluid-handling facilities, increased environmental concerns, and eventually well shut-in (with associated workover costs). Consequently, producing zones are often abandoned in an attempt to avoid water contact, even when the intervals still retain large volumes of recoverable hydrocarbons. Many polymer systems have been applied over the years to control undesired water production from hydrocarbon wells, with varying degrees of success. For approximately eight years, a polymer gel system based on an acrylamide/t-butyl acrylate copolymer (PAtBA) crosslinked with polyethyleneimine (PEI) has been used successfully for various water shutoff applications. This article describes results from a sampling of over 200 jobs performed throughout the world, including the average results from more than 90 jobs performed in one geographic location alone. In addition to "standard" matrix treatments, results will be shown for other types of treatment, including a design to plug annular communication and a combination of sealant and temporary gel in an openhole horizontal completion. In addition, laboratory data pertaining to work aimed at increasing the temperature limit of the system will be presented. The upper placement temperature of the system originally was ~260°F. Data presented in this article indicates the development of a retarder system that allows the upper placement temperature to be raised to at least 350°F. Introduction Controlling water production has been an objective of the oil industry almost since its inception. Produced water has a major economic impact on the profitability of a field. Producing 1 bbl of water requires as much or more energy as producing the same volume of oil. Often, each barrel of produced water represents some lesser, but significant, amount of unproduced oil. In addition, water production causes other related problems such as sand production, the need for separators, disposal and handling concerns, and the corrosion of tubulars and surface equipment. Many methods are available to mitigate water-production problems, and perhaps the most widely used chemical system has been chrome-crosslinked polyacrylamide gels. A previous publication described the advantages of the acrylamide- (PAtBA) copolymer/polyethyleneimine system (herein referred to as OCP, or organically crosslinked polymer) (Hardy et al. 1998). A brief discussion of these advantages follows, with presentations of case histories using OCP and data showing expansion of OCP technology. OCP System Description Gel systems for water and gas shutoff have many requirements, including:Low viscosity allowing easy injection deep into a formation matrix.Capability to control gelation time of the fluid.Sufficient strength to resist drawdown in the wellbore.Temperature stability of the gel for extended periods of time. As will be shown in the following discussion, the OCP system meets all these requirements. The viscosity of the system is ~25 cp as mixed. This relatively low viscosity is due to the relatively low molecular weight, ~250,000, of the PAtBA. This polymer is covalently crosslinked with PEI, which results in excellent control over gelation time. Sufficient strength and temperature stability are also obtainable. In addition, the OCP system is insensitive to formation fluids, lithology, and/or heavy metals. Another advantage of the OCP system is its predictable viscosity profile that can be used to improve diversion over long treatment intervals.
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