DESALINATION CONCENTRATE DISPOSAL INJECTION WELL EXPERIENCES IN THE USA AND CARIBBEAN. Abstract

Transcription

1 DESALINATION CONCENTRATE DISPOSAL INJECTION WELL EXPERIENCES IN THE USA AND CARIBBEAN Robert G. Maliva, Schlumberger Water Services, 1567 Haley Ln, Suite 202, Fort Myers, FL 33907, Ph: William S. Manahan, Schlumberger Water Services, Fort Myers, FL Abstract Injection wells may be a viable disposal option for desalination concentrate where favorable hydrogeological conditions exist and environmental protection regulations allow for the practice. The key technical issues for injection well systems are that the well(s) must reliably and economically provide the target disposal capacity over the life of the membrane treatment plant, and that injection should not cause environmental harm, particularly the contamination of fresh groundwater resources. Successful implementation of deep well injection thus requires identification of an injection zone that has both a high enough transmissivity to efficiently accept the concentrate flows and effective confinement from aquifers that might be used for drinking water supplies. Clogging is a primary operational concern for injection well systems in general. Adverse fluid-rock interactions may result in mineral precipitation and alteration that can clog pores and reduce system capacity. Technical challenges and opportunities lie in optimization of well design, construction, and operational procedures (e.g., pretreatment) to maximize injection well performance and reliability. Introduction Identifying and developing an economic, environmentally sound, and permittable method for the disposal of waste flows is a critical feasibility and design issue for membrane desalination systems. Injection wells may be a viable disposal option where favorable hydrogeological conditions exist and environmental protection regulations allow for the practice. Deep well injection may be the only economical disposal option at inland areas where a surface water outfall or blending with wastewater are not viable options. The key technical issues for injection well systems are that the well must reliably and economically provide the target disposal capacity over the life of the membrane treatment plant and that injection should not cause environmental harm. The overriding environmental concern is that injected liquid wastes must not migrate into, and contaminate, potential drinking water sources. A review was performed of some desalination concentrate injection wells in the United States and Caribbean. A diversity of well designs have been employed for concentrate disposal wells including angle and horizontal directionally drilled wells. Historical injection well experiences and knowledge of regional and local geology allow for an initial screening of injection well feasibility in a given area and identification of potential well design options. The design of injection well systems should be integrated with the desalination system design, rather than as separate elements. The recovery of the process design will impact the volume and quality of the concentrate generated by the plant. Water quality requirements for deep well injection, for 1

2 example, may impact treatment system design. In general, the design and operation of injection well systems are much more complex than that of production wells. Regulatory Issues The construction and operation of injection well systems requires regulatory approval. Countries differ as to whether they either have enacted regulations and permitting requirements specific to injection well systems or address injection wells through a general environmental impact assessment process. In the United States, the Safe Drinking Water Act (1974), and subsequent amendments, require the U.S. Environmental Protection Agency (USEPA) to establish a system for the regulation of underground injection activities, which resulted in the formation of the USEPA Underground Injection Control (UIC) program. The overall objective of the USEPA UIC program is to prevent endangerment of Underground Sources of Drinking Water (USDWs). A USDW is defined as a non-exempted aquifer that contains water with less than 10,000 mg/l of total dissolved solids. Endangerment is considered an activity that results in the presence of any contaminant such that it results in non-compliance with any national or state primary drinkingwater regulation. With respect to desalination concentrate injection, there are two basic options. The concentrate may be injected into a non-usdw aquifer, which typically contains greater than 10,000 mg/l of TDS, or it can be injected into a USDW aquifer provided that the discharge either meets primary drinking water standards or the concentrations of constituents of concern in the discharged water are below the concentrations in the ambient (native) groundwater. Concentrate injection wells are categorized as either Class I or Class V. Class I injection wells, by definition, inject liquid wastes beneath the lowermost formation containing, within one-quarter mile of the well bore, a USDW. Class V is a very broad category that includes all injection wells not included in Classes I through IV and VI. Concentrate might also be disposed of in Class II injection wells, which are defined as wells used for the disposal of water produced during oil and gas production and for enhanced recovery of oil or natural gas. In general, Class I injection wells have stricter construction and monitoring requirements than Class V wells. In practice, there are four regulatory types of injection wells used for concentrate disposal in the United States (Figure 1). Class V injection wells are divided herein into types, A, B, and C: Class I inject below the deepest USDW Class V, Type A inject into a USDW aquifer, typically containing brackish water Class V, Type B inject into a non-usdw aquifer that is underlain by a USDW aquifer Class V, Type C inject into a non-usdw aquifer in a location where USDWs do not occur. A key issue for Class I injection wells is that upward vertical migration of injected fluids must not occur into overlying USDW aquifers. Class V, Type A injection wells have the constraint that the concentrate must meet either primary drinking water standards or have the concentrations of chemical constituent be less than those in the ambient groundwater, which is often not practically possible. Class V, Type C injection wells have the least constraints because there are no nearby USDWs that may be endangered. For disposal within shallow coastal aquifers, offshore seepage of injected concentrate might be a regulatory concern. 2

3 Figure 1. Concentrate injection well types There is interest in using existing Class II injection wells for concentrate disposal, particularly in Texas. Depleted oil fields occur in many parts of the state, and oil-field operators already have considerable experience injecting oil-field brine wastes in these fields (Mace et al. 2005; Nicot & Chowdury 2005). Costs would be low, as existing wells would be used, environmental impacts would be negligible to non-existent, and many fields are located near water-scarce, small- to large-sized communities. Key issues are the geochemical compatibility of the concentrate with the native waters and minerals in the injection zone and potential injection rates. Oil-field injection wells are usually operated at much lower injection rates than the concentrate flows generated at municipal desalination plants. From a regulatory perspective, concentrate could be used in lieu of other water sources for oilfield water flooding operations. The desalination plant owner/operator would need assurances that the oil/gas field operator could consistently accept the target volume of concentrate for a set period of time. Alternatively, no longer needed Class II injection wells could be repermitted as Class I injection wells, if they meet Class I construction and mechanical integrity standards. However, this has not been done to date in the United States. Injection Well Design Injection wells are constructed in a similar manner as production wells. The well drilling method used depends largely upon the well site and local geology. Underground injection control regulations may require additional casings strings. For Class I injection wells, a surface casing that seals off the USDWs is normally required. Class I injection wells used for concentrate disposal are considered industrial disposal wells and are required to have a tubing and packer design. Depending upon the hydrogeology of the injection zone, injection wells may be completed with either an open hole, screen, liner, or perforations. Injection wells need to be designed to maximize well efficiency, which means minimizing head losses during injection from frictional losses within the casing and during flow into the formation. The bottom-hole pressure in the well during injection should be close to the increase in the adjoining formation. Head losses within the casing can be reduced by increasing the casing diameter. A more important issue is 3

4 minimizing head losses as the injected water passes through the screen and filter pack and enters the formation. Screens (if used) need to be selected or designed with sufficiently large total open areas to minimize head losses. Screens should ideally be over-designed so the well injection capacity can be maintained even after some clogging. The well design should also accommodate the expected need for periodic well rehabilitation. Perforated completions involve the use of shaped charges to penetrate (deform) the casing and crush the cement and adjacent formation. Aquifers are heterogeneous and contain zones of relatively high and low permeability. The most permeable intervals of the formation should be perforated, which can be identified via high resolution borehole geophysical logging. The advantages of perforated completions are that they allow for detailed selection of production and injection intervals, drilling related formation damage can usually be bypassed (perforations may extend through formation damage and into the formation), and that additional perforations can be made at a later time (Bellarby 2009). In general, the preferred (most efficient) completion is an open hole or an open hole with an uncemented liner. Concentrate Injection Wells in the United States and Caribbean Florida Hydrogeological conditions for the disposal of concentrate by deep well injection are ideal in South Florida because of the presence of the so-called boulder zone of the Lower Floridan Aquifer. The boulder zone is a sequence of fractured dolomites (Figure 2), located approximately 2,500 to 3,500 feet below land surface, that has extraordinarily high transmissivities and well capacities (Maliva and Walker 1998). Some individual wells used for wastewater disposal have capacities in excess of 20 million gallons per day (MGD) with wellhead injection pressure of less than 100 psi. A single injection well may be able to accept the entire concentrate flow from a brackish water desalination plant, although a second well is commonly installed for back-up capacity. Upward migration of injected concentrate has not been documented for concentrate disposal wells largely due to its relatively high salinity and thus density. Upward migration of injected liquid wastes in South Florida is driven largely by buoyancy. Modeling results have demonstrated that injected, low-salinity, municipal wastewater tends to migrate upwards in the seawater-salinity injection zone and confining strata, whereas high-salinity concentrate is more stable (Maliva et al. 2007). Class I injection wells are also used for concentrate disposal from brackish water desalination plants in the Tampa Bay region of east-central Florida using the Avon Park permeable zone ( Zone C of Hickey 1982) as an injection zone. Peninsular Florida is underlain by the Floridan Aquifer System, whose upper part contains fresh or brackish water and is thus a USDW. Class V, Type B injection wells are uncommonly used for concentrate disposal in coastal areas where the shallow aquifer contains groundwater of seawater salinity. Examples of shallow Class V, Type B concentrate disposal injection wells are systems on Little Gasparilla Island on the Gulf of Mexico Coast and the City of Highland Beach system on the Atlantic Coast. The latter consists of two injection wells constructed with 15-inch PVC injection casings set to ft and open holes to ft (CH2M Hill 2008). The injection zone is the Pleistocene Anastasia Formation, which is quartz-rich limestone or calcareous sandstone. A shallow (150 ft deep) injection well system is also used on Marathon in the Florida Keys, which uses the reefal Key Largo Limestone as an injection zone. 4

5 Figure 2. Downhole video image of the boulder zone (Hialeah, Florida) Texas Deep well injection is used for concentrate disposal at the Kay Bailey Hutchison Desalination Plant in El Paso, which is the largest inland desalination plant in the world. The brackish groundwater desalination plant officially opened August 8, 2007 and has a finished water design capacity of 27.5 MGD. The injection well system consists of three wells completed in fractured dolomite (Silurian Fusselman and Montoya Formations, Silurian; Hutchinson 2008). The injection wells are permitted as Class V (Type A), as the salinity of the injection zone is less than 10,000 mg/l, but the wells are constructed to Class I injection well standards. The injected water has a TDS of less than 8,000 mg/l, and is injected under gravity. Any two wells could be used for injection for the plant s design concentrate flow of 3 MGD. Deep well injection will be used for concentrate disposal for the San Antonio Water System (SAWS) Brackish Groundwater Desalination Plant. Phase One of the project will produce 12 MGD of drinking water and upon completion of Phases Two and Three, the plant will have a production capacity of 30 MGD. The injection wells will be Class I and discharge into the Edwards and upper Glen Rose Limestones. The wells will have total depths of 5,000 to 5,300 feet, be completed with approximately 800 feet of open hole, and have a target capacity of 450 gpm each (Stein 2014). Kansas Class I injection wells are used in Kansas for the disposal of the effluent from reverse-osmosis treatment and other liquid wastes. The Kansas Department of Health and Environment allows only gravity injection and does not permit the use of pumps to increase the injection pressure. Gravity injection is required as it allows only the amount of fluid that the formation can naturally accept, prevents pressure buildup in the disposal zone, and significantly limits the potential for induced seismic activity. Deep ( 4,800 ft) Class I concentrate disposal injection wells have been constructed in Garden City (Wheatland Electric Cooperative) and Hutchinson, Kansas. Both 5

6 systems use the Arbuckle Formation, which consists of sequences of dolomites, limestones, and occasional sandstone units as an injection zone. Oil and gas disposal wells are common in parts of Kansas. The Class I injection wells were constructed using oil and gas well drilling and construction methods. Angle well drilling was used in the Garden City well to increase the total length of the hole in the Arbuckle Formation to 1,425 ft (the formation is 780 ft thick at the RO plant location). The wells are completed with a perforated liner. Colorado Deep Class I injection wells have recently been constructed in Colorado for reverse-osmosis concentrate disposal. The wells are of oil-field design with perforated completions. The East Cherry Creek Valley Water & Sanitation District Northern Project Class I injection well has a total depth of about 10,380 ft with a target capacity of 200 to 400 gpm and injection pressure of psi (Kaunisto et al. 2010). Secondary concentration of RO concentrate using brine minimization was employed to reduce the concentrate flow to 3 to 6% of the raw water flow, which minimizes the water rights loss and the number of deep disposal wells required (Rynders 2011). The City of Sterling constructed two Class I injection wells with total depths of approximately 7,000 ft. The wells had a target capacity of 350 gpm, but through the use of advanced formation evaluation techniques and completion workflows, the well capacity was increased to 2,000 gpm. Hawaii Injection wells have historically been widely used in Hawaii for the disposal of wastewater, with most of the wells privately owned and operated. The aquifers in Hawaii are volcanic rock with some overlying sedimentary rocks, referred to as caprock. A key distinction in Hawaii is between exempted aquifers and USDWs. The division between exempt and USDW aquifers on the islands is mapped as a UIC line. Class V (Type C) injection wells may be constructed seawards ( Makai ) of the UIC line and are prohibited landwards ( mauka ) of the UIC line (i.e., in USDWs). Voids may be encountered during drilling and it is required that it be verified that voids do not slope landwards (i.e., towards USDWs). The Shores at Kohanaiki desalination plant, which started operation in November 2008, has eight groundwater production wells and one injection well, and is permitted to reinject up to 0.7 MGD. The volcanic injection zone crops out off shore, and an important technical issue is that the salinity of the injected water matches as closely as possible to the salinity of the native groundwater to minimize the potential change in salinity in near shore waters. California California generally lacks high-transmissivity carbonate aquifers that are used elsewhere as injection zones. Class V injection wells discharging into coastal shallow beach or dune sands are a viable disposal option for small-capacity systems. A vertical injection well was used at the City of Marina desalination plant (which was subsequently mothballed). The injection well reportedly had severe scaling problems (AWWA 2011). The Sand City desalination plant (0.6 MGD) disposes of concentrate using a 6-inch diameter, 700 foot horizontal well installed parallel to the beach, 30 ft bls. The well was installed below coastal dunes. The plant was designed to maintain a brine salinity below seawater quality (35 g/l) and may require dilution with raw water when 6

7 salinity is high. The horizontal well was designed to not affect the existing freshwater/seawater interface or increase salinity in the bay. Deep high-pressure injection wells are a potential concentrate disposal option in California. The City of Los Angeles Terminal Island Renewable Energy Project investigated the feasibility of injection of slurry mixtures of varying ratios of digested residuals, biosolids wetcake, and concentrated brine from alternative water supply systems into a deep sand formation. The wells are of oil-field design with perforated completions. The expected average injection rate is 10 bbl/min (420 gpm) and average injection pressure is 4000 psi (Bruno et al. 2011). Two hundred eighty (280) million gallons were injected by mid 2014 (City of Los Angeles 2015). Arizona Arizona, as one of the driest states in the Unites States, has a need for desalination. Concentrate disposal is a primary challenge facing desalination in Arizona (Eden et al. 2011). All aquifers in Arizona are designated by default as drinking water sources, so a permit for deep well injection would require a demonstration that the aquifer is isolated and only contains water that is unsuitable for drinking. An additional issue is that the Phoenix basin contains large deposits of salt. Caverns left over from mining are potential disposal zones, but there is a concern that toxic ions in concentrate might compromise future salt production (Eden et al. 2011). The Arizona Department of Environmental Quality has historically looked unfavorably on deep well injection for concentrate disposal, but is now willing to consider applications (Eden et al. 2011). Caribbean Islands Vertical injection wells are used for concentrate disposal in Caribbean Island nations including the Bahamas, Barbados, and Cayman Islands. The injection zone on Grand Bahama Island is a cavern system between depths of 400 and 600 ft bls, formed during Pleistocene sea level lowstands. The cavernous interval has been used for wastewater disposal for over 40 years, and some wells have capacities as high as 10 MGD (Cant 2012). Vast volumes of water flow through system, which dilute the wastewater prior to open-marine discharge. The surficial freshwater occurs down to a maximum of about 110 feet is a protected zone in the central Bahamas. The next 150 feet is reserved for seawater extraction with the reject zone extending below 400 feet (Cant 2012). Elsewhere in the Caribbean, a lesser separation of production and injection zones has been successfully used. For example, at the Ellsmere/Hyatt site on Cayman Island, the base of the production zone for the seawater supply wells ranges from 65 to 92 ft bls, while the top of the injection zone occurs at a depth of about 100 ft bls (Missimer and Winter 2003). Confining strata and the greater density of the concentrate compared to water within the production zone prevents short-circuiting of the concentrate into the raw water. Concentrate Volume Reduction Liquid waste can be treated to varying degrees to reduce its volume. It can be more cost-effective to treat concentrate further to reduce its volume than to construct additional injection well capacity. High recovery systems were defined by Mickley (2008) to have recoveries of 92% or greater. Liquid wastes can also be treated to the extent that only a solid residue remains. Zero liquid discharge (ZLD) methods are of particular interest for inland desalination facilities in which other conventional disposal options are not feasible. Volume minimization and ZLD 7

8 systems for desalination facilities were recently reviewed by Mickley (2006, 2008), Bond and Veerapaneni (2007), and Bond (2010). ZLD systems commonly involve high recovery processes to increase freshwater production and reduce concentrate volume, followed by one or more steps to reduce the concentrate to a solid, which may include brine concentrators, crystallizers, spray dryers, and evaporation ponds. The greatest costs associated with ZLD are often the final steps to reduce high salinity brines to a solid. There are additional costs associated with the disposal of the solids if they cannot be put to a beneficial use. High recovery desalination systems increase the concentration of all solutes in the raw water including contaminants and other constituents of regulatory concern. Very high levels of recovery could increase the concentration of some constituents (e.g., arsenic, radionuclides) to such an extent that the wastestream exceeds thresholds for being considered a hazardous or radioactive waste, which, in some jurisdictions, may preclude underground injection (Mickley 2008; Carollo 2009). As salt concentration increases, scaling of membranes and other treatment elements with sparingly soluble salts and silica becomes increasingly problematic. The main salts of concern are calcium sulfate, calcium carbonate, silica, and barium sulfate. Scale inhibitors are usually used, which allow systems to operate at supersaturated levels without precipitation. Scale inhibitors lose their effectiveness with increasing degrees of supersaturation. Scaling could clog injection wells, in some instances, essentially irreversibly. Hence, a detailed geochemical evaluation, including modeling of fluid-rock interactions, is critical for injection of concentrate from high recovery systems. Conclusions Injection wells have been demonstrated to be a cost-effective and reliable means for the environmentally sound disposal of desalination concentrate. However, injection wells are inherently more complex to successfully design, construct, and operate than production wells because often chemically dissimilar water is being forced into the formation. Deep well injection requires favorable hydrogeological conditions for the wells to be able to reliably accept target flow rates over the planned operational life of the desalination plant and to prevent the injected water from impacting potential drinking water sources. The most favorable condition for an injection zone is a carbonate (limestone or dolomite) formation zone with well-developed secondary porosity and an associated high transmissivity. The major operational challenge of concentrate injection wells is loss of injectivity due to clogging. Any suspended or dissolved material present in the injected water must pass through a relatively small surface area, the borehole wall. Failure to adequately address all design and operational performance criteria can result in an under-performing system and, in some instances, irreversible well and formation damage. Carbonate aquifers have the advantage that injection wells can be readily rehabilitated through acidification. Sand and sandstone aquifers tend to be less transmissive and more susceptible to clogging with these types of injection wells either having low capacities or high injection pressures. Technical challenges and opportunities lie in the optimization of well design and construction and operational procedures (e.g., pretreatment) to maximize injection well performance and reliability. 8

9 References AWWA (2011) Desalination of Seawater. Manual of Water Supply, Practices M61, Denver, AWWA. Bond, R. (2010) Zero-liquid discharge: desalination of water with high organic content, IDA Journal, v. 2, no. 2, pp Bond, R., and S. Veerapaneni (2007) Zero liquid discharge for inland desalination, Denver, AWWA Research Foundation. Bruno, M.S., J. Couture, J., and J.T. Young (2011) Concentrate and brine management through deep well injection, Proceedings 26th Annual WateReuse Conference, Phoenix, AZ Sept 11-14, Cant, R.V. (2012) The Bahamas use of deep wells for effluent disposal, and as a source of seawater usable for multi-purposes, Caribbean Water and Wastewater Association 21st Annual Conference and Exhibition, Paradise Island, Bahamas, Oct 1-5, 2012 Carollo (2009) Water desalination concentrate management and piloting West Palm Beach, Florida, South Florida Water Management District. CH2M Hill (2008) Assessment of the feasibility of shallow demineralization concentrate disposal in coastal areas of the St. Johns River Water Management District: Literature review, Palatka, St. Johns River Water Management District Special Publication SJ2009-SP3. City of Los Angles (2015) Deep Well Injection: T.I.R.E., Eden, S., T.W. Glass, and V. Herman (2011) Desalination in Arizona a growing component of the state s future water supply portfolio. Arroyo (Water Resources Research Center, College of Agriculture and Life Sciences, University of Arizona) 2011, pp Hickey, J.J. (1982) Hydrogeology and results of injection tests at waste-injection test sites in Pinellas County, Florida. U.S. Geological Survey Water-Supply Paper Hutchinson, W.R. (2008) Deep-well injection of desalination concentrate in El Paso, Texas, Southwest Hydrology, March/April 2008, pp Kaunisto, D., K. DiNatale, K., and D. Brown, D. (2010) Planning, Permitting and Design of an Inland Brackish Groundwater Supply Project, 25th WateReuse Symposium, September 12-15, 2010, Washington, D.C. Mace, R.E., J.-P. Nicot, A.H. Chowdhury, A.R, Dutton, and S. Kalaswad (2005) Please pass the salt. Using oil fields for the disposal of concentrate from desalination plants, U.S. Department of the Interior Bureau of Reclamation. Technical Service Center, Desalination and Water Purification Research and Development Program Report No. 112 Maliva, R.G., and C.W. Walker (1998) Hydrogeology of Deep-Well Disposal of Liquid Wastes in Southwestern Florida, U.S.A., Hydrogeology Journal, v. 6, pp Maliva, R.G., W. Guo, and T.M. Missimer (2007) Vertical migration of municipal wastewater in deep injection well systems, South Florida, U.S.A, Hydrogeology Journal, v. 15, p Mickley, M.C. (2006) Membrane concentrate disposal: practices and regulations (2nd Edition) Denver, U.S. Department of the Interior, Bureau of Reclamation. Mickley, M.C. (2008) Survey of high-recovery and zero-liquid discharge technologies for water utilities, Alexandria, VA, WateReuse Foundation. 9

10 Missimer, T.M. and H. Winters (2003) Reduction of biofouling at a seawater RO plant in the Cayman Islands, Proceedings of the International Desalination Association World Conference on Desalination and Water Reuse, BAH Nicot, J.P., and A.H. Chowdhury (2005) Disposal of brackish water concentrate into depleted oil and gas fields: a Texas study, Desalination, v. 181, no. 1, pp Rynders, T. (2011) Design and Piloting of a Brine Minimization System for Concentrate Disposal, 56th Annual New Mexico Water Conference, December 13-14, 2011, Alamogordo, NM. Simonitch, R. (2011) Seawater Desalination in California: The Sand City Approach. West End Event - Green Lecture Series (August, 2011). Stein, B. (2014) San Antonio Water System Brackish Groundwater Desalination Project, Groundwater Protection Council 2014 UIC Annual Conference. Wetterau, G. (2009) Tapping the Ocean in Monterey, CA: The Sand City Desalination Facility, 24th Annual WateReuse Symposium, Seattle, WA, September