1、 API PUBL*lb23C 9b = 0732290 0559151 622 = Optimization of Hydrocarbon Recovery API PUBLICATION 1628C FIRST EDITION, JULY 1996 sF4- Strategies for Todays E nuironmental Partnership American Petroleum Ins titute s docu- menting performance improvements; and communicating them to the public. The found
2、a- tion of STEP is the API Environmental Mission and Guiding Environmental Principles. API standards, by promoting the use of sound engineering and operational practices, are an important means of implementing APIs STEP program. API ENVIRONMENTAL MISSION AND GUIDING ENVIRONMENTAL PRINCIPLES The memb
3、ers of the American Petroleum Institute are dedicated to continuous efforts to improve the compatibility of our operations with the environment while economically developing energy resources and supplying high quality products and services to consum- ers. The members recognize the importance of effi
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11、ment API PUBLICATION 1628C FIRST EDITION, JULY 1996 American Petroleum Ins titute API PUBL*Lb28C b 0732270 0557154 331 SPECIAL NOTES API publications necessarily address problems of a general nature. With respect to par- ticular circumstances, local, state, and federal laws and regulations should be
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24、or written permission from the publishel: Contact the Publisher; API Publishing Services, 1220 L Street, N. W, Washington, D.C. 20005. Copyright O 1996 American Petroleum Institute API PUBL*Lb28C 96 0732290 0559355 278 FOREWORD MI publications may be used by anyone desiring to do so. Every effort ha
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27、eet, N.W., Washington, D.C. 20005. iii API PUBL*lb2C 96 0732290 0559256 204 = CONTENTS Page SECTION 1-INTRODUCTION . 1 SECTION 2-LNAPL MIGRATION . 1 SECTION 3-GOAL DEFINITION AND THE EFFECT ON OPTIMIZATION . 4 3.1 General 4 3.2 Factors Affecting Remedial Goals . 4 3.3 Remedial System Evaluation Crit
28、eria . 5 3.4 Factors Affecting Optimization Complexity . 5 SECTION “APPROACHES TO REMEDIATION AND OPTIMIZATION . 5 4.1 General 5 4.2 Containment and Withdrawal of Dissolved Hydrocarbons . 5 4.3 LNAPL Recovery 10 4.4 Residuals Remediation and Venting 15 SECTION 5-ADDITIONAL CONSIDERATIONS 17 5.1 Coup
29、ling of Systems . 17 5.2 Cost Considerations in Optimization 17 5.3 Optimization Questions . 18 APPENDIX A-BIBLIOGRAPHY . 19 Figures 1-Vertical Distribution and Degrees of Mobility of Hydrocarbon Phases in Earth Materials 2 2-Hydrocarbon Distribution in Formation and Monitoring Well 3 3-Relationship
30、 Between Wetting Fluid Saturation and Relative Permeability . 4 this is called residual LNAPL or residual hydrocarbon. (Note: In this document, the terms LNAPL and oil are used interchangeably.) The LNAPL will also volatilize and form a vapor phase, assum- ing that the hydrocarbon mixture has a vola
31、tile component. If a water table is present, as the LNAPL migrates vertically in the pore spaces of the formation, it will encounter pores filled with water. Due to the differences in density and cap- illary pressures, it will begin to accumulate and a two-phase flow system, consisting of water (the
32、 wetting phase) and LNAPL (the non-wetting phase), will develop. Figure 1 presents a conceptual illustration of the distribu- tion of water, LNAPL. and air in a porous medium, as pre- sented in API Publication 1628, i. The continuous pore volume is occupied by water, LNAPL, and/or air and the spaces
33、 between represent the porous medium. Several zones are present in the porous medium: a. A three-phase zone containing water, LNAPL, and air, where the relative saturations of the three fluids will deter- mine the mobility of each. This section is considered part of the vadose or unsaturated zone. b
34、. A two-phase zone, or capillary zone, containing water and LNAPL, where the relative saturation of these fluids will determine their mobility, c. A two-phase zone below the water table, but within the limits of water-table fluctuations, where residual hydrocar- bons are present. d. A one-phase zone
35、 containing only water at some distance below the water table and outside the zone of water-table fluctuations, where only dissolved hydrocarbons are present. The primary zone of lateral movement of LNAPL near the water table is the two-phase zone water and LNAPL), where LNAPL saturation can reach a
36、 high enough level to become mobile. Figure 2 shows the relative saturation curves for water and LNAPL in this zone and the relation- ship to LNAPL accumulation in a monitoring well. In gen- eral, there is an over-accumulation of LNAPL in the well relative to the formation; this accumulation can be
37、calcu- lated through the saturation-capillary pressure relationships Chiang and Kemblowski, 2; Fm, et al., 3). This concept of a two-phase system where both water and LNAPL occupy the pore spaces is extremely important in the evaluation of remedial systems and the recovery of LNAPL. The ability of t
38、he porous medium to transmit flu- ids (its permeability) is a function of the relative saturation of the two fluids and is referred to as relative permeability. Relative permeability involves the flow behavior of two immiscible fluids existing in the same porous medium. It means that as the saturati
39、on of one fluid decreases relative to the second fluid, its flow capacity will also decrease. Thus, as the saturation of LNAPL decreases relative to water, the 1 API PUBL*lb28C 9b W 0732290 0559158 T87 D 2 API PUBLICATION 16286 HORIZONTAL MOBILITY OF HYDROCARBONPHASES LIQUID VAPOR DISSOLVED Immbile
40、Mope Mobile (.) I I 1 Mobile Immobile T Immobile i 4 Mobile Zone of water table fluctuation LEGEND Free hydrocarbons - y - Effective water table - 0 Sand grain B Water Liquid hydrocarbons 0 AirNapor (*) During infiltration or due to unsaturated flow GENERALIZED CROSS SECTION FLUID SATURATION Unsatur
41、ated zone with I residual hydrocarbons and hydrocarbon vapor Hvdrocarbon I 1.3 Capillary zone with free liquid hydrocarbons Limit of L immobile / n hydrocarbons Water table fluctuation zone I with residual hydrocarbons Saturated zone with dissolved hydrocarbons Source: Modified from Lundy and Gogel,
42、 1988. (FROM API PUBLICATION 1628, AUGUST 1989) Figure 1 -Vertical Distribution and Degrees of Mobility of Hydrocarbon Phases in Earth Materials API PUBLX162C 96 W 0732290 0559359 933 OPTIMIZATION OF HYDROCARBON RECOVERY 3 ability of the LNAPL to flow will also decrease (as shown in Figure 3). The r
43、elative saturation of the LNAPL (the non- wetting phase) must reach a certain level for it to become mobile; then its mobility and relative permeability increases rapidly with increased saturation. The increase in relative permeability of the wetting phase (water) is more gradual and proportional to
44、 the incremental increase in saturation. The relative permeability effect, coupled with the entrap- ment of LNAPL below the water table and residual losses in the unsaturated zone, result in the relatively low recoverabil- ityof LNAPL. Average Oil Thickness Residual LNAPL losses are very important t
45、o overall remediation at a site. In addition to residual losses that occur above the water table in the unsaturated zone, fluctua- tions of the water table will also result in entrapment of LNAPL below the water table. Fine-grained sands tend to retain more of the liquids in a residual state than co
46、arse- grained sands. The type of hydrocarbon also impacts LNAPL residuals, and residual LNAPL tend to increase with more viscous products. These residual LNAPL are immobile and remain as a source of dissolved and vapor phase concentrations. Monitoring well f t 7- Water ywater O Saturation 1 Figure 2
47、-Hydrocarbon Distribution in Formation and Monitoring Well API PUBLrLb28C 96 m 0732290 055Lb0 635 m 4 API PUBLICATION 1628C 100 lo- 10-2 .- L. 9 E g 10-3 .- 2 d - al c Ca - 10-4 10“ IO“ 0.0 0.2 0.4 0.6 0.8 1 .o Wetting fluid saturation Figure 3-Relationship Between Wetting Fluid Saturation and Relat
48、ive Permeability SECTION 3-GOAL DEFINITION AND THE EFFECT ON OPTIMIZATION 3.1 General Establishing the goals or cleanup target levels for the remediation of a site is of primary importance since the goals determine the selection of the remedial technology. An example would be a one-acre site, locate
49、d in an arid environment, with a 200-foot depth to groundwater, with 1.0 part per million (ppm) of benzene in the soil, that origi- nated from a gasoline release. If the goal at this site is to achieve cleanup target levels that provide an acceptable level of risk to human health and the environment, the opti- mal solution based on a risk assessment may be no further action or monitoring only. On the other hand, if the goal is to achieve regulatory-driven benzene levels of 5 parts per billion (ppb) in the soil in one year, venting may be se
