Abstract:
An automated high speed drill cuttings processing and injection module having a relatively small foot print, capable of operation in zone 1 hazardous environments, for injecting drill cuttings into an earth formation. Capable of handling high drilling rate cuttings surges. The process including conveying systems, holding and slurry tanks, circulating pumps, high speed grinding mill, high pressure injection pump, fragmentation system and automation system for controlling electrically driven injection pump having automatic speed control regulation with torque and horsepower limiting features. Thereby allowing high speed injection without plugging the formation while still allow for high pressure formation fracturing when necessary. The processing system further insures cuttings slurry homogenization and entrained particle size to less than 100 micron for both hard and soft particles. Being unitized the system reduces installation cost dramatically. The system further provides continuous automatic control, measures and records hole cleaning, viscosity, slurry density, as well as surface and bottom-hole pressure.

Description:
This application is a continuation-in-part of application Ser. No. 08/896,205, filed Jul. 17, 1997, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the collection and processing of drill cuttings separated from a drilling rig&#39;s solids control system and more particular to the processing and injections of such cuttings into fractures in the earth formation adjacent the well being drilled via the annulus between a well casing and well bore or into other such cuttings disposal scenarios. 
     2. General Background 
     In the oil and gas drilling industry the processing of drill cuttings and their disposal has been a logistics and environmental problem for a number of years. Various systems have been developed for handling and processing the cuttings for disposal and reclamation. Such systems include returning the cuttings via injection under high pressure back into the earth formation in a manner such as that described in U.S. Pat. Nos. 4,942,929, 5,129,469 and 5,109,933, and the treatment of drill cuttings as disclosed by U.S. Pat. Nos. 4,595,422 5,129,468, 5,361,998 and 5,303,786. However, in practice, the injection process is not as simple as it may seem. The preparation of the cuttings into a homogeneous mix which is acceptable to high pressure pumps used in pumping material down a well is essential. Transforming the cuttings into a pumpable slurry is complicated by variable drill rates producing large volumes of cuttings at times thereby creating surges in drill waste materials, the need to pump the slurry at high pressures into the earth and/or formation fractures hundreds if not thousands of feet below the surface. Complications also arise due to the need for constant velocity and high horsepower while pumping. On offshore platforms space is at a premium. Therefore, cuttings treatment units must be compact and as light in weight as possible. Solids control equipment is most often placed in hazardous areas, near the well bore, where large horsepower internal combustion engines are not permitted due to the possibility of high gas concentration. Therefore, any additional equipment used for processing solids must meet stringent explosion proof requirements for such areas of the rig. 
     Heretofore, cuttings injection has not gained wide acceptance in offshore drilling operations such as may be found in the North Sea, primarily due to the problems discussed above and the inefficiency and ineffectiveness of the cuttings preparation and injection processes. 
     Although, other cuttings processing system have been developed for preparing drill cutting for disposal and some have been tried in an attempt to inject such processed drill cuttings into a well bore, as is disclosed by U.S. Pat. Nos. 4,942,929, 5,129,469, and 5,109,933 and 5,431,236. However, none combine, individually or collectively all of the advanced features, required for problem-free cuttings injection, disclosed herein by the instant invention. 
     The problems associated with cuttings injection are numerous as expressed by Warren in U.S. Pat. No. 5,431,236. Starting with processing of the cuttings for injection, we find that the particles are not uniform in size and density making the slurification process very complicated. The cuttings mixture often plugs circulating pumps, the abrasiveness of the cuttings also abrade the pump impellers causing cracking, some attempts have been made to use the circulating pumps for grinding the injection particles by purposely causing pump cavitaion, thereby shortening pump life, hard cakes build up in tanks creating circulation problems and circulation pumps cavitate unexpectedly due to irregular particle size. Therefore, it is known that a uniform particle size of less than 100 micron must be maintained for proper formation injection at the well site. Maintaining such consistency with hard and soft materials is very difficult. The use of shear guns to reduce particle size as taught by Warren does not insure consistency and requires continuous recalibration thereby reducing the volume capacity of the processor. Warren also teaches that sand should be separated through the use of hydrocyclones which further reduces throughput volume. 
     Next we find that since no two earth formations are alike it is very difficult to prevent plugging of the formation fractures in the well bore especially when there are long delays in placement of the injection slurry in the formation. Plugging of the formation fractures often occurs as a direct result of large particle size, often in the range of 300 micron or greater, combined with high pressure high volume applications. Plugging of the well formation results in extensive well drilling downtime which is very expensive. 
     Cuttings injection failures have occurred primarily due to the inability to, handle large volumes of cuttings surges, fine tune the injection process by providing particle size control, uniform slurry density and to provide volume and pressure control over the injection process. Further, attempts to inject cutting slurries into the earth have met with failure as a result of the inability to manually control all facets of the process and injection operation. As a result of such failures most offshore drilling operators in the North Sea have ban the practice and have resorted to using expensive synthetic drill fluids. 
     It is to this end that the present invention has been developed, the proprietary know-how of which has been maintained until disclosed herein thereby, disclosing a unique efficient system and method for injecting drill cuttings into an offshore oil and gas well in a drilling environment requiring compactness, relatively light weight, low maintenance, full automation and operability in hazardous potentially explosive environments. 
     SUMMARY OF THE INVENTION 
     The instant invention has overcome the problems of the prior art and has proven itself by successfully performing cuttings processing and injection in wells where others have failed under identical conditions. The instant invention relates to a drill cuttings processing and injection system for use in hazardous oil and gas well drilling environments where compactness, smooth high performance injection pumping which provides zero downtime and volume variability, and where reduced maintenance are essential. In accordance, a modular processing system is provided comprising a shaker package, a grinder and/or roll mill package, a slurrification control package, Slurrification tanks, transfer pump package, injection pump package, air control system , hydraulics package, and Electrical package. The self-contained system transfers drill cuttings from the drilling rig&#39;s cuttings shaker discharge trough to the system slurrification package where the cuttings are further processed for injection, via a high pressure pump, deep into the earth&#39;s formation. These and other aspects of the present invention together with certain advantages and superior features thereof may be further appreciated by those skilled in the art upon reading the following detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a further understanding of the nature and objects of the present invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings, in which, like parts are given like reference numerals, and wherein: 
     FIG. 1 is a side elevation of the process module; 
     FIG. 2 is top view of the process module; 
     FIG. 3 is schematic diagram of the process system; 
     FIG. 4 is a cross section view of the holding tank particle fragmentation system; and 
     FIG. 5 is a cross section view of the flow path of the cutting slurry into the earth formation via a well bore annulus; 
     FIG. 6 is a front elevation of a second embodiment of the cuttings and injection module; 
     FIG. 7 is a top view of the second embodiment illustrated in FIG. 6; 
     FIG. 8 is a right side view of the embodiment illustrated in FIG. 6; 
     FIG. 9 is a left side view of the embodiment illustrated in FIG. 6 taken along sight line  9 — 9 ; 
     FIG. 10 is a partial section view of the embodiment illustrated in FIG. 6 taken along sight lines  10 — 10 ; 
     FIG. 11 is a partial exploded view of the arrangement shown in FIG. 10; 
     FIG. 12 is a cross section view taken along the sight line  8 — 8  in FIG. 10; 
     FIG. 13 is schematic diagram of the process system of the second embodiment illustrated in FIGS. 6-9; and 
     FIG. 14 is an isometric view of an alternative injection pump. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning first to FIG.  1  and FIG. 2 we see the invention  10  comprises a processing module  12  which, when assembled, is self contained and fully operational for operation on an offshore drilling location. The Module  12  system as best seen in FIG. 3 further comprises an in-feed cuttings conveyor  14  or other such means which feed overflow drill cuttings  5  from a drilling rig&#39;s drilling fluid mud recovery system&#39;s shell shakers to the process module  12  where the cuttings  5  are deposited into a first slurry tank  16 . The tanks are configured with special baffles and a conical lower portion to prevent plugging and caking of the solids and increase the speed in which the cuttings in a slurry are feed to the grinder pumps  18 , 19 . The cuttings slurry  15  is agitated and ground by the centrifugal shredding or the grinding pumps  18 ,  19  located adjacent the slurry tank  16  where water is added as necessary to provide a pumpable slurry solution. The slurry  15  is then pumped via either of the two grinding pumps  18 , 19  to a system shale shaker  20  where the slurry  15  passing through the shale shaker&#39;s screens is fed to a second slurry tank  22 , where it is further agitated and mixed, or to a holding tank  24 . Overflow entrained cuttings which do not pass through the shale shaker&#39;s  20  screens is gravity fed to a roll mill  26  where the oversize cuttings  5  such as sand, limestone and shale are instantaneously ground into fine particles and fed back to the first and second slurry tanks  16 , 22 . This high speed milling operation performed by roll mill  26  serves to significantly reduce particle size to a uniform consistence, thus reducing the possibility of restricted flow rates caused by irregular size particles entrained in the slurry during the cutting&#39;s  15  first pass through the slurry tanks  16 , 22 . A third pump  28  is provided for recirculating slurry  15  between the holding tank  24  and the two slurry tanks  16 , 22 . The second circulating pump  19  also serves as backup for the first grinding pump  18  thus allowing either of the slurry tanks  16 , 22  to be the primary tank. Pumps  18  and  19  are fitted with special oversize impellers having large tungsten carbide particle impregnated matrix coatings to prevent cracking and wear. These large impellers shred the cuttings  5  in a manner whereby the softer cuttings are degraded and become entrained in the slurry immediately. Cavitation of the pumps  18 , 19  is purposely avoided thus reducing wear and cracking of impeller blades. Connection lines are provided for feeding the homogenous slurry, resulting from thorough mixing and slurry particle reduction, to a high pressure injection pump  30  for injection into the annulus  44  of a well bore  46  and ultimately into the earth formation  48  as seen in FIG. 5 or to cement pumping operations if needed. A hydraulics package  32  is provide for driving conveyor motors and an electrical control package  34  is provided for operations of all AC operated equipment. i.e. agitation motors, pump motors, sensors, etc. 
     A special electrical AC/DC “Speed Control Regulator” (SCR) package  36  is provided for controlling the large, electrical motor driving the high pressure triplex or piston type injector pump  30 . This type of motor control has been widely used for industrial plant systems for many years. However, SCR systems have not been employed in the offshore oil and gas industry for drill cuttings  5  injection use in Hazardous locations. It has been found that due to its complexity, its maximum horsepower and speed limitations and its ability to meet class  1  zone  1  hazardous location requirements SCR drives are ideal for such applications. Such zone classifications are used in the industry to designate potentially hazardous gas locations which could become flammable. Hazardous locations are generally limited to equipment having heavy gas-tight enclosures for all electrical apparatus. Therefore, in this case zone  1  on an oil or gas well drilling platform is considered more hazardous than zone two due to its closer proximity to the well head (generally within 50 feet) would require a much higher safety factor with regard to the equipment&#39;s probability of causing sparks which could ignite gases emitted from the well. 
     Problems with such drives in the past have more recently been overcome with the more common use of solid-state circuitry and computer logic systems making such systems less complicated and maintenance free. The SCR system  36  is ideally suited to this particular operation due to its ability to control a wide range of motor speeds, adjustable torque control, excellent speed regulation, dynamic braking, fast, stable response to changing load conditions encountered in deep well pumping operations, horsepower limiting, pressure limiting on well cuttings injection, high efficiency and automatic operation. 
     A very high horsepower drive, in the 1000 horsepower range, is required for driving the high volume injection pump  30 . The injection pump  30  has a discharge pressure of up to 15000 PSI. Several types of injection pumps may be used including triplex and large displacement piston pumps. The prior art usually utilizes a large direct drive diesel engine located in zone  2  (semi-hazardous area) or an inefficient hydraulic drive motor powered by a remote engine or an explosion proof electric motor and pump package as a drive means approved for location in zone  1  areas. However, hydraulic drives have proven to be incapable of controlling high pressure injection pumps of this magnitude (over 200 horsepower) in a satisfactory manner. Primarily due to their high maintenance, heat, inefficiency and noise levels. Noise levels being restricted to 80 decibels or less on offshore drilling rigs in the North Sea increases the difficulty of their use. 
     The instant invention utilizes a direct coupled electric motor drive for the injection pump  30  controlled by the Speed Control Regulation system  36 . The Speed Control Regulation (SCR) system  36  allows an explosion proof motor to be close coupled to a high pressure injection pump. The SCR system is then controlled electrically by a programmed computer system. Thereby providing small foot print, light weight, constant or variable horsepower and torque at selected operating speeds thus reducing surging and stalling of the cuttings injection pump process. There are several methods which may be used to provide speed control for drive motors coupled to the triplex injection pump. For example an engine driving a DC generator which in turn drives a DC driving motor having speed control capability. A second options may be the use of an AC motor driving the DC generator, an AC frequency controlled motor drive, or an AC motor with SCR capability. In any case the advantages of an electric speed controlled drive system far exceeds that of a hydraulic pump and motor drive. 
     Automated electrical speed control and pressure controls allow other control systems to be implemented which are computerized to assist in automating and controlling the injection process system. Therefore, it is possible to fully automate the process based on formation reaction information. Such a system has many advantages, for example, automation of the system&#39;s injector pump speed and torque also prevents formation plugging and is interlocked to protect the well from over pressurization. The systems may also be run at very low speed and low pressure thereby preventing large formation fractures. However, when the need arises high pressure and high horsepower can be applied to fracture the formation. 
     It is also important to have the ability to leave the slurry in the formation for long periods without plugging the formation or the casing annulus. Therefore, a process has been developed and included into the system for automatically injecting premixed gels having yield strength and fluid loss properties into the slurry solution thereby allowing for formation sensitivity. Such automatic injection may be programmed to a predetermined rate based on formation requirements or to meet real time changing conditions. 
     Automation further allows computer control of multiple processes thereby drastically reducing or eliminating the need for excessive manning of the system on a constant basis, thus reducing cost of operation. 
     It is highly desirable to reduce the entrained particle size to less than 100 micron in order to insure long term success of cuttings injection and significantly increase the cuttings volume a well will receive. The smaller the particles size the less plugging and fracturing occurs in the earth formation. Therefore, an important feature of the injection process module  12  is its ability to size and fragment cuttings particles suspended in the slurry  15  at high speed and pressure and thereby preventing constipation of the drill cuttings  5  processing system. This feature prevents shutdowns of drilling operations due to cuttings out flow plugging. One aspect of this high speed process includes an impingement system whereby a line  38  is connected to the discharge line of the injection pump  30  is routed to the holding tank where it is divided into two nozzles  40  which are directed onto heavy plates  42 . When necessary this line  38  may be charged at high pressure, thus directing discharge flow from the injection pump  30  directly into the holding tank  24  via said nozzles  40 . The entrained cuttings then strike the heavy plates  42  at high velocity thus fragmenting such particles making the slurry even more homogeneous. This system further serves to hydrate the introduced gel chemicals and enhance the fluidity of the drill cuttings  5  thus aiding in slurry preparation and to provide cuttings slurry  15  quality control. 
     The second embodiment  50  as illustrated in FIG. 6 perform the essentially the same function as the first embodiment  10 . However, this arrangement provides a more compact and efficient unit. For example the holding tank  24  and the two slurry tanks  16  and  22  have been unitized. As seen in FIG. 6 the holding tank  52  occupies one end of the skid  54 . A lower portion of the holding tank  52  is removed, as seen in FIG. 8 to provide a space for the super charging and recirculating pump  28 . The two slurry tanks  56 , 57  occupy the remaining portion of the skid  54  adjacent the holding tank  52  separated only by a petition  58 . The slurry tanks  56 , 57  have sloping bottoms  60 , as seen in FIG. 9, extending the width of the skid  54 . This allows room to mount the grinding pumps  18 ,  19  below the tanks. This arrangement allow the width and the height of the skid  54  to be kept to a minimum while maintaining maximum capacity. Thereby producing a smaller foot print where space is at a premium. To improve service ability, quick couples  62  are provided on all pump connections thus allowing fast pump clean out and/or replacement. As seen in FIG. 7 the shaker  20  is mounted above the holding and slurry tanks  52 , 56 - 57  which allows for easy access and visual inspection of the tank interiors via screen decks  64 . Turning now to FIG. 10 we see a somewhat different arrangement of the particle size control apparatus which takes the place of the high pressure impingement system illustrated in FIG. 4 of the first embodiment  10 . This embodiment  50  utilizes the grinder pumps  18  and  19  to direct the slurry  16  upwards through a stand pipe  66  which is removable by disconnecting the deck plate  68  and uncoupling the quick couple  62  the stand pipe is coupled to a replaceable nozzle  70  via a pipe union  72 . The slurry  16  is then directed towards a replaceable impingement member  74  having a conical portion therein which is in turn connected via threaded rod  76  and pin  78 . The impingement member may therefore be adjustably lowered into close proximity with the nozzle  70  by simply turning the hand wheel  80  connected to the threaded rod  76 , thus adjusting the particle size of the slurry  16 . As seen in FIG. 11 this arrangement not only allows the slurry  15  particle size to be adjusted from the top of the tanks  56 , 57  but also allows quick removal for cleaning or replacement of the stand pipes  66 , nozzle  70  and impingement member  74  from the top of the tanks  56 , 57 . As seen in FIG. 12 the threaded rod  76  is supported by removable, threaded nut, assemblies  100  mounted to frame members  98 . 
     It should also be noted that by having the slurry tanks  56 , 57  located adjacent the holding tank  52  separated only by a common partition which is slightly below the level of the surrounding walls thereby allowing the slurry  16  in the holding tank to overflow into the slurry tanks  56 , 57  if necessary. 
     As seen in FIG. 6 piping  82  leading from the outlet of the super charging pump  28  may be directed via a valve  84  to the stand pipe  66  located in the first slurry tank  56 , thereby further reducing the particle size of the slurry in the holding tank. Piping  86  is also provided in each of the slurry tanks as seen in FIG. 11 which directs flow of the slurry from the grinding pumps  18 , 19  back to the vibrator screen  20  via valve  88  where the cuttings were first delivered via a transfer system  14  for separation. The shaker or vibrator screen  20  delivers all fluids and particles of a predetermined size passing through the screen as underflow directly to the holding tank, while the oversize cuttings materials are discharged as overflow into the cuttings slurry tanks  56 , 57  for processing by the grinding pumps  18 , 19  and the particle quality assurance system controlled by the impingement and recirculating system discussed above. 
     As seen in FIG. 13 the second embodiment further includes both temperature sensors  96  and viscosity and density sensors  94  located in each of the slurry tanks and controllers for same. It is also anticipated that chemicals used for controlling the viscosity of the slurry  16  may be piped via line  102  into each of the slurry tanks  56 , 57  as well as waste water  104  and sea water  106  or fresh water to control the density. 
     As previously explained herein the injection pump  30  may be replaced by a piston or cylinder intensifier pump such as that illustrated in FIG.  14 . This type of pump  200  utilizes a double acting hydraulic cylinder assembly  202  having dual rods one extending from each end of the piston thereby forming a double rod cylinder. Each rod is then enclosed or encased in a product cylinder  204  having inside diameter slightly larger than the rod diameter. Thereby intensifying the force of the cylinder rod by the difference between the hydraulic cylinder piston displacement and rod displacement multiplied by the hydraulic pressure. Each product cylinder  204  is fitted with a pipe tee fitting  206  at one end whereby a check valve  208  is attached to the each of the two remaining ends. An inlet manifold line  210  is connected to one of the check valves  208  at each product cylinder  204  in a manner whereby the manifold line  210  is also connectable via a quick coupling  212  to the drill cuttings tank. An outlet manifold line  214  is also connected to the remaining check valve  208  at each product cylinder  204  in a manner whereby the manifold line  214  is also connectable via quick coupling  216  to the well head injection line. The hydraulic cylinder  202  is connected to a hydraulic power unit and valve system having electric sensors and controls which alternately stroke the cylinder  202 . The linear configuration of the pump unit  200  allows the unit to fit snugly within the confines of the skid package of the units  12  and  50  discussed herein. 
     Because many varying and different embodiments may be made within the scope of the inventive concept herein taught, and because many modification may be made in the embodiments herein detailed in accordance with the descriptive requirement of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in any limiting sense.