Abstract:
A water blending system and associated method for a gas shale well is provided, which includes a first inlet pipeline that receives water from a freshwater source. The first inlet pipeline has a first valve. A second inlet pipeline receives flow back water and has a second control valve. A third pipeline receives water flow from the first and second pipelines. The first pipeline has a salination level detector, the third pipeline flowing water into a tank; wherein the water flow of the first and second inlet pipelines is adjusted based on a salination level detected by the salination level detector.

Description:
STATEMENT OF RELATED APPLICATION 
       [0001]    The present application claims the benefit of priority under 35 U.S.C. 119(b) to Canadian Patent Application Serial No. 2750776 filed Aug. 26, 2011, in the name of inventor David J. Elliot, entitled “Frac Water Blending System”, all commonly owned herewith. 
       FIELD 
       [0002]    This invention relates to the provision of water for use with gas shale wells, and more particularly for provision of frac water therefor. 
       BACKGROUND 
       [0003]    Hydraulic stimulation (fracture) is used in shale gas wells by using frac water to stimulate, or fracture the shale. Frac water includes either fresh water, or a blend of fresh and ‘flow back’ water. Flow back water is water that has previously been pumped into the shale formation, and is returned to the surface during testing and production periods. The flow back water generally contains dissolved solids, typically with high concentrations of dissolved salts. Flow back water can be generally reused if the salinity level, as measured in parts per million (ppm) is below a certain threshold. Generally, this threshold is in the range of 30,000-90,000 ppm, and in some applications may be even higher. Higher salinity levels mean higher fluid friction, making the water more difficult to pump at high pressures. 
         [0004]    It is difficult to accurately and easily blend two streams of water (fresh and flow back) into an output stream with a consistent desired salinity level. Previous solutions have been to pump individual streams of fresh and flow back water into a frac water tank (such as a Westeel™ c-ring), circulate the water, and constantly sample the water for salinity. The challenge is that fresh and salt water tend to stratify due to the difference in density, and they tend to separate with the heavier salty water sinking to the bottom of the tank. This makes getting a true water sample difficult as the water may not have blended well. It is also typically a manual operation, with many inaccuracies, and is also not energy efficient due to the increased pumping power needed for agitation (mixing) of the water. 
       SUMMARY 
       [0005]    The invention provides a means to maximize the flow back water that is reused, and maintain the maximum salinity allowed, in order to minimize the use of fresh water, use less energy than in previous methods and provide a more consistent blending of both streams of water. 
         [0006]    The system according to the invention blends the flow back water and fresh water prior to entering the tank, and discharges water with the correct salinity into the tank. The system includes an intake pipe for fresh water, an intake pipe for flow back water, with control valves on each pipe, a junction of the two streams and a long mixing pipeline which mixes the water either by making use of the turbulent flow regime of the individual streams of water from each intake pipe, or the mixing pipeline can be configured with agitation plates for mixing the incoming streams of water (useful if the flow is laminar), as well as a conductivity meter that measures the salinity levels of the mixed stream of water. The input water streams can be throttled with the valves to achieve the desired salinity (or conductivity) as displayed on the meter. 
         [0007]    There are several ways of adjusting the intake pipelines. As an example, two different modes may either provide for maximum flow back water flow or maximum fresh water flow. If the maximum water flow is desired, then typically the fresh water pipeline valve will stay at maximum open and the flow back water pipeline valve will be throttled to provide the maximum salinity permitted; and if the maximum reuse of flow back water is desired, then the flow back water pipeline valve is open to its maximum and if the resultant salinity is higher than the maximum permitted, the fresh water pipeline valve is gradually closed to achieve the permitted salinity. Therefore, the mixing of the flow back water and fresh water depends on the flows of the two pipelines, the flow back water salinity and the resultant salinity permitted. An operator may have confidence that the frac water being used for fracture stimulation is indeed at the correct salinity level, and maximum reuse of the flow back water is achieved, which is best for the environment, and for longevity of the industry. 
         [0008]    The system according to the invention is portable and can be installed quickly, and it allows a large flow rate while under high pressure. The control valves can be automated with a simple algorithm, or can be manually controlled. Flow meters are used to track values of fresh and flow back water used for reporting purposes. The system is compatible with commonly used open top tank systems currently being used in the industry, with a small modification of the discharge/blending tube to discharge into a manifold or directly into a closed top tank. 
         [0009]    A water blending system for a gas shale well is provided, including: a first inlet pipeline receiving water from a freshwater source, the first inlet pipeline having a first valve; a second inlet pipeline receiving flow back water, the second inlet pipeline having a second control valve; and a third pipeline, receiving water flow from the first and second pipelines, the first pipelines having a salination level detector, the third pipeline flowing water into a tank; wherein the water flow of the first and second inlet pipelines is adjusted based on a salination level detected by the salination level detector. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a top view of a blending pipe system according to the invention; 
           [0011]      FIG. 2  is a side view thereof; 
           [0012]      FIG. 3  is a rear view thereof; and 
           [0013]      FIG. 4  is a flow chart showing a control process using the system. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    The system, as shown in  FIGS. 1 through 3 , includes support skid  100  which structurally supports the system, and provides contact with the ground surface. Skid  100  provides stability, and may be an oilfield skid with features such as winching ears and lifting points, allowing skid  100  to be moved easily. 
         [0015]    Fresh water intake pipeline  110  and flow back water intake pipeline  120  lead into discharge pipeline  130 . Fresh water intake pipeline  110  receives water from a fresh water source. Flow back water intake pipeline  120  receives water that had previously been pumped into the shale formation, and has been reclaimed. Discharge pipeline  130  is configured to run the mixed water flow over wall  140  of tank  150  to allow the mixed water to enter tank  150  for use as frac water. 
         [0016]    Fresh water intake pipeline  110  and flow back water intake pipeline  120  are configured according to the incoming water system parameters, such as flow rates. In general, the water should enter pipelines  110 ,  120  via approximately  10 ″ pipelines. Pipelines  110 ,  120  and  130  may be made from high-density polyethylene (HDPE) or stainless steel and may be internally coated with steel to resist the corrosiveness of the flow back water. The pipe diameter reduces along pipelines  110 ,  120  as they approach junction  230  to increase the velocity of the water therein and provide a full pipe cross sectional flow as may be required by flow meters  190 ,  200 . Control valves  170 ,  180  are positioned downstream of flow meters  190 ,  200 . By-pass tubes  210 ,  220  may be placed to relieve pressure on pipelines  110 ,  120 , if required. 
         [0017]    Pipelines  110 ,  120  join and form a single discharge pipeline  130  at junction  230  wherein the fresh water and flow back water mix. Discharge pipeline  130  may include agitation plates (not shown) to assist in mixing the two incoming water streams. The mixed water is directed up and over the wall  140  of tank  150  by discharge pipeline  130 . Conductivity probe  240  is positioned near the top of discharge pipeline  130  (above the high water level) and several pipe diameters downstream of junction  230  to ensure that the water is well mixed. The mixed water is horizontally discharged into the depths of tank  150  to provide for mixing of the water within tank  150 . 
         [0018]    Siphon tubes  300 ,  310  may be used to break the continuity of the water flow between tank  150  and discharge pipeline  130  in case remedial work is necessary or should pipeline  130  be disconnected. Siphon tubes  300 ,  310  allow water to be easily emptied from discharge pipeline  130 . Drain port  315  is also present to drain discharge pipeline  130  easily. 
         [0019]    Flow meters  190 ,  200  may be magnetic flow meters, which require no moving parts, and are not susceptible to fouling from harsh water conditions. Meters  190 ,  200  are used to track total and instantaneous flows of the two input water streams from pipelines  110 ,  120  and can serve as part of the automated system for control of the water streams. Conductivity probe or salinity meter  240  measures the conductivity of the output mixed water stream in pipeline  130 . The conductivity level is displayed in a convenient location, and water conductivity can be converted to a salinity level. Meter  240  can be configured to display salinity in PPM or uS/cm (micro Siemens/Centimetre). 
         [0020]    Flow meters  190 ,  200  and conductivity probe  240  and display may be powered by a solar panel and/or a 24V battery system built into skid  100  or by a power system located at a control center nearby. 
         [0021]    As shown in  FIG. 4 , in use, the system, either manually or automatically, first determines the salinity level of the mixed water flow in discharge pipeline  130  (step  1000 ). If the sanity level is at an acceptable level between predetermined maximum and minimum salinity levels (step  1050 ), no action is taken (step  1100 ). 
         [0022]    If the salinity level is greater than the acceptable maximum salinity level (step  1050 ), then either the freshwater intake pipeline flow is increased and/or the flow back water intake pipeline flow is decreased using control valves  170 ,  180  (step  1200 ). Then the salinity level is determined again (return to step  1000 ). 
         [0023]    If the salinity level is less than the acceptable minimum salinity level (step  1050 ), then either the freshwater intake pipeline flow is decreased and/or the flow back water intake pipeline flow is increased using control valves  170 ,  180  (step  1300 ) depending on whether maximum flow or maximum flow back water reuse is desired. Then the salinity level is determined again (return to step  1000 ). Flow rates are considered in determining either the maximum flow rate or the maximum reuse of flow back water, which depends on the flow of the fresh and flow back water streams and the incoming water salinity. 
         [0024]    Alternatively, if the salinity level is greater than the maximum wanted, then the flow back water flow is decreased or the fresh water flow is increased (step  1200 ). Again the end goal of the user, be it to maximize the overall flow rate, or maximize the use of flow back water, will affect the determination. 
         [0025]    For example, two desired modes of operation my be to achieve maximum flow of water to tank  150  or the maximum reuse of flow back water, depending on the volume of water needed for frac purposes, and while maintaining the desired salinity levels between and maximum and a minimum. In the first mode, to obtain maximum flow of water to tank  150 , the fresh water valve  170  remains at the maximum open position and the flow back water valve  180  is adjusted to the maximum level at which the maximum salinity level permitted is reached. In the second mode, the maximum reuse of flow back water, the flow back water valve  180  remains at the maximum open position and if the resultant salinity is higher than the maximum level permitted, then the fresh water valve  170  is gradually adjusted to achieve the desired salinity. The valve adjustments thus depend on the flows of the individual streams, the flow back water salinity level and the resultant salinity permitted 
         [0026]    The system can also be configured to mix the water in tank  150  to further reduce salinity levels by having pipeline  120  receive water from a bypass pipeline drawing water from tank  150 . 
         [0027]    The above-described embodiments have been provided as examples, for clarity in understanding the invention. A person with skill in the art will recognize that alterations, modifications and variations may be effected to the embodiments described above while remaining within the scope of the invention as defined by claims appended hereto.