Abstract:
Used drilling fluids, drilled cuttings and salt contaminated soil, etc., are processed for disposal or reuse by staged water-washing and solids separating procedures which are monitored for the salinity of the water contacting the particles and are repeated to the extent necessary to obtain selected low values, in order to produce saline wash water suitable for injecting into a disposal well and size-graded substantially salt-free materials suitable for construction operations or non-hazardous waste disposal.

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part of assignee&#39;s copending application Ser. No. 926,023, filed Oct. 31, 1986, now abandoned on &#34;A Process for Treating Drilled Cuttings.&#34; 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to a process for training used drilling fluids and drilling cuttings, particularly those in which the salt content is high enough to present a disposal problem. More particularly, the invention relates to a staged water washing and solids removal process for converting used salt water drilling fluids, drilled solids and/or drilling fluid mud pit residues to a source of desalinated solid particles of selected sizes suitable for uses as, for example, construction or restoration materials, or for disposal as a non-hazardous waste. 
     In various regions, tanks are used for storing drilling fluids and cuttings because reserve pits are not permitted. In addition, removal may be required from presently existing reserve pits. In such reserve pits, the used drilling fluid contents are mixed with, or contaminated by, top soil and the material used in constructing the pits. The present process avoids the onerous expense of hauling such materials from reserve pits or tanks to hazardous waste disposal locations which may be hundreds of miles from the drilling sites. 
     SUMMARY OF THE INVENTION 
     The invention relates to a process for converting components in drilled cuttings to substantially non-saline solid materials, which may be reused in some useful manner, or disposed of as a non-hazardous waste material. The drilled cuttings components are mixed and agitated with water in successive steps to separate substantially all of the larger particles in a variety of size ranges and to suspend the very fine particles in water. The largest particles are separated and washed with water. The slurry resulting from separation of the largest particles is mixed and agitated with additional water, and particles of various sizes are removed in successive steps of mixing, agitating and separating. In each of these succeeding steps, where the salinity of water on or draining from the separated particles is insufficient to provide a salinity level acceptable for reuse of the materials, or for disposal as a non-hazardous waste, both the mixing and agitating of the various sized particles with fresh water and the separating of a given size range of particles are repeated, to the extent necessary, to provide such a salinity reduction. The separated particles are collected, either by size range, or all together, prior to disposal or reuse. The remaining slurry water containing only very fine particles is reused in the separation process or in some other useful manner, or disposed of in some environmentally acceptable manner. 
     For convenience, the term &#34;drilled cuttings&#34; is used herein to refer to used drilling fluids, drilling solids and/or drilling fluid mud pit residues and/or slurries of such materials. As used herein, the term &#34;salinity&#34; of a substance refers to an amount of disssolved or soluble salt, such as an alkali or alkaline earth metal, which, in solution, releases the same number of ions that would be released by the same amount of sodium chloride (NaCl). Drilled cuttings commonly contain NaCl, potassium chloride (KCl), magnesium chloride (MgCl 2 ), and calcium chloride (CaCl 2 ), and the present process is well suited for reducing the salinity due to any or all of such salts. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The drawing is a flow sheet for a preferred embodiment of the present process. 
    
    
     DESCRIPTION OF THE INVENTION 
     The present invention is, at least in part, premised on a discovery that the presently described combination of procedures and devices are advantageous relative to various other combinations. For example, the ojective of desalinating the components of drilled cuttings might be accomplished by subjecting those components to (a) aggregate washing equipment combined with a clarifier or (b) subjecting such components to such washing equipment combined with mud plant and solids control devices. 
     It was found that the first option, utilizing the clarifier was significantly less efficient in handling fine materials because when isolated, the fine materials have a water content higher than those of the same material isolated by means of solids control equipment. Because of that, less salt would be removed during each cycle through the clarifier and more recycling would be needed to reach a selected reduced salinity. In addition, when the fresh water consumed per pound of salt removed is compared, a clarifier does not perform as well as solids control equipment. 
     The drawing illustrates a particularly suitable treatment of drilled cuttings components by means of a combination of aggregate washing equipment and mud plant solids control equipment in accordance with the present invention. As shown, the salt contaminated materials being treated are dumped from trucks into hopper 1 which feeds a conveyer, such as a belt, for carrying the material to a blade mill and screen 2. 
     A suitable blade mill is basically a horizontal tub which encloses a conveyor shaft on which are mounted screw flights and paddles. The purpose of such a blade mill is to precondition material for separation by forming a slurry of the drilled cuttings. Water is introduced to saturate the materials uniformly while the paddles agitate, scrub, and abrade the material so that lumps are broken up and the individual particles form a slurry. The slurry drops onto a screen associated with the blade mill, where jets spray water onto the cuttings. In the illustrated embodiment, particles which are generally larger than sand size and have average diameters greater than about 3/8-inch, are separated by the screen and are transported to a stockpile. The wet or water-suspended slurry of finer particles that pass through the screen associated with the blade mill are fed, preferably by a chute (not shown), to a sand screw means 3. 
     A sand screw of the type shown separates particles such as coarse sand-sized particles between about 150 mesh and 3/8-inch from finer materials. A suitable form of such a sand screw includes a base tub in which the materials enter and an inclined tub that contains an auger. The particles are subjected to a tumbling action of the rotating continuous screw flights of the auger and an introduction of a rising current of fresh water into the base tub of the sand screw means. A suspension of the finer particles are carried upward by a flow of water and pass over a weir into a mixing tank while the coarser particles are conveyed by the auger and are substantially drained and squeezed dry of water, for example, to a water content of about 18-25 w%. 
     In the preferred embodiment, the salinity of the water drained from the coarse sand-sized particles is measured by an electrical resistivity measuring device (not shown) arranged to control a flop gate 4 for directing separated particles to either a stockpile or a salty particle return. If the water drained from, or remaining on the surfaces of such particles, has a salinity equivalent to no more than a selected target concentration, such as less than about 2500 ppm NaCl equivalent, the particles are sent to a stockpile. The target concentration may be set by criteria for non-hazardous waste disposal. 
     Where the salt concentration of such water (which amounts to a salt-leaching water which contacted the particles) is higher than the target concentration, the particles are returned for remixing and reseparation within the sand screw 3, as indicated by the arrow labeled &#34;salty particle return.&#34; Such remixing and reseparating is repeated until a selected level of salt concentration is reached. During this processing, feeding of the new batches of contaminated materials into the hopper 1 and on the blade mill 2 may be delayed. 
     The water suspended slurry of particles smaller than about 150 mesh are conveyed to a mixing tank 5 in which the water is circulated by a pump 6. More water is added to the suspension, preferably until a precentage of the suspended solids within the liquid is about 5 to 7% by volume, and is within the operational constraints of a relatively fine solids control means, such as a desander 7 and desilter 8. As known in the art, the concentration of such slurried particles can be measured manually by vaporizing water from the slurry or automatically by means of gauges of the types used in municipal sewage plants. The slurry is displaced by pump means 9 into desander 7. 
     A suitable desander consists of a series of tapered cones in which solid particles are separated from liquid by means of the centrifugal force generated by the swirling of the slurry inside the cones. The solid particles exit through the tapered end of the cones while the liquid flow out the top. The desander 7 is preferably arranged to remove isolated fine sand-sized particles having average sizes in the range of about 80-100 microns to 150 mesh. Most of the liquid and the clay and silt-sized or smaller particles are displaced by pump 10 into the desilter 8. 
     The water draining from, or left on the surfaces of the relatively fine sand-sized particles separated from desander 7, is measured for salinity by a measuring device (not shown) which controls flop gate 11 to direct those particles onto the shaker 12 or, where the salinity is equivalent to a value higher than the target concentration, to tank 13. In that tank, the salty particles are mixed with relatively fresh water circulated by pump 14, and delivered through the salty particle return line to a point upstream of the desander for redilution and reseparation within the desander. 
     The slurry of substantially clay and silt sized particles, which may have sizes ranging from about 12 microns to about 80-100 microns, are separated in desilter 8 in a manner analogous to that of desander 7. The separated clay and silt-sized particles are similarly measured for salinity and directed by a flop gate 15 to either the shaker 12, when their salinity is equivalent to or less than a selected target value, or to tank 16, in which they are mixed with fresh water circulated by pump 17 through the salty particle return line for redilution and separation in desilter 8. 
     The slurry water separated by desilter 8 is preferably monitored for salinity and where it is substantially fresh water, it is either directed through the water recycle line 19 for reuse. Where the water is unsuitable for reuse in the process, it is directed to some environmental acceptable disposal, such as injection into a saltwater disposal well 18 for underground injection. The water could also be used in a secondary recovery water flooding operation, or for some other useful purpose. 
     A suitable shaker 12 is arranged to receive the relatively fine sand-sized particles from desander 7 or clay and silt sized particles from desilter 8, and to allow any free moisture to drain through the shaker screen and return to tank 13. The particles separated from shaker 12 are conveyed to a stockpile. 
     In the illustrated embodiment of the present invention, substantially salt-free particles from drilling fluid cuttings are made available for some useful purpose, such as the construction of well site access roads, drilling pads or central production facilities, etc. In the winter the sand-sized materials can be used for sanding roads. Very fine materials having no construction value can be added to topsoil or tilled with other soils for restoration of construction or drilling sites. Other useful purposes are considered to be within the scope of the invention. Alternatively, the separated particles may be disposed of in a manner suitable for non-hazardous wastes. 
     The present invention is particularly applicable to the treating of salt water muds and drilled cuttings saturated with saline fluid or substantially any mixture containing significant proportions of dissolved and granular salt, as well as the reserve pit residues inclusive of the drilling fluid permeated layers of soil underlying such mud pits. Examples of suitable types of drilling fluids include any brine mud made from water and commercially prepared salts or brine water produced in association with oil and gas. 
     In general, the equipment such as pumps, screens, blade mills, sand screws, desanders, desilters, shakers, and the like, can be substantially any of the currently available devices or techniques designed for use in oil field operations such as the drilling of oil and concrete batching operations. Examples of particularly suitable items of such equipment include the SWECO 12 cone desilter, Model PO4C12, and Brandt SE-10 desilter; SWECO 2 cone desander, Model P10C02, and Brandt SRC-2 desander; Kolberg Series 8000 Log Washer blade mill, and Eagle 18-inch×24-foot blade mill; Eagle 44 in. Single Screw Washer-Classifier-Dehydrator sand screw, and Kolberg Series 5000 Sand Prep, Single Screw sand screw. 
     Where desirable or necessary, the present process can be operated to reduce the salinity of the produced solid materials to salinities significantly lower than 2500 ppm NaCl equivalent. In a preferred operation, the recycling stages are repeated to the extent necessary to reduce the salinities to less than about 1000 ppm NaCl equivalent.