Solid control equipment mainly refers to equipment used to remove harmful solid phases in drilling fluid, such as drilling fluid shakers, sand removers, desilters, mud cleaners, and drilling fluid centrifuges.
Mechanical equipment cannot remove most of the cuttings that return to the ground. It is very costly to keep the cuttings in a suitable range. Dilution becomes the main method to solve the solid phase problem. The performance of solid control equipment can be understood through calculation. A simple mass balance calculation, the volume added is equal to the volume discarded. This calculation depends on the drilling fluid treatment system that the solid control equipment can remove 100%, 90%, 80%, or 70% of the cuttings back to the ground. Obviously, 100% removal efficiency is not possible because at the same time a part of the liquid phase is retained in the cuttings. The above percentages simply show the methods and concepts of solid control efficiency.
The average volume concentration of drill cuttings in the waste fluid was 35%. The underflow solid phase volume concentration from the sedimentation drilling fluid centrifuge and drilling fluid mud cleaner is 55% to 63%, and the underflow solid phase volume concentration from the desilter and sand remover is about 35%. The solid phase volume concentration of the waste liquid shaker coarse mesh screen is about 45%, and the solid phase volume concentration of the waste liquid fine mesh screen is about 20%. Taking all these solid control equipment into consideration, the volume concentration of drill cuttings is about 35%. For coarse-mesh screens, most of the fluid is removed when the fluid passes through the drilling fluid shaker to remove large particles. Therefore, although the total volume of screened cuttings is small, the volume concentration of the waste solid phase is much larger than that through the fine screen Solid phase volume concentration. The finer the mesh size, the more drill cuttings and drilling fluids are removed. The reason is related to the specific surface area of the cuttings. For example, if a golf ball is taken from a drilling fluid, it will carry very little drilling fluid. However, when the ball is broken into small pieces, its volume of adsorbed liquid will increase sharply. The total volume of drill cuttings does not change, but the surface area varies greatly. As the surface area increases, the more liquid is absorbed. In order to test (1) the amount of waste material, (2) the volume of clean drilling fluid needed to dilute the cuttings, and (3) the volume of the newly configured drilling fluid, the removal efficiency of the four cuttings will be discussed separately, respectively 100%, 90%, 80% and 70%
1.100% solid phase removal efficiency of solid control equipment
In the example where the solid phase removal efficiency is 100%, all drill cuttings are returned to the ground and all are removed by solid control equipment. In addition to the cuttings, the drilling fluid adsorbed on the surface of the cuttings is also removed. As 35% volume cuttings are removed, the waste will also contain 65% drilling fluid. As shown in Figure 1, because the cuttings and part of the drilling fluid are removed from the system, the level of the drilling fluid pool will also drop (assuming the demonstrated porosity and compressibility are zero). Because drilling fluid systems do not contain cuttings, there is no need to use clean drilling fluids in Lacey. However, 286bbl drilling fluid is needed to replenish the material removed from the system to keep the liquid level of the tank constant, and the volume concentration of drill cuttings is reduced at this time. In other words, the cuttings content will not and cannot be maintained at 4%. In the previous example, 40bbl of cuttings in the drilling fluid were dispersed into 1100bbl of drilling fluid (100bbl of new borehole volume newly drilled on the 1000bbl initial volume machine). The solid content of the cuttings will be 3.6%, (400bbl / 1100bbl) × 100%. The ratio of cleaning fluid required per 1bbl of cuttings is 2.86 (286bbl / 100bbl). In this example, the drilling fluid containing 4% of the cuttings will be diluted and the volume concentration of the cuttings will be reduced.
2.90% solid phase removal efficiency of solid control equipment
Under the condition that the solid phase removal efficiency is 90%, the new cuttings removed from the system is 90bbl. It is further assumed that the volume concentration of drill cuttings in the waste is 35%, and the total volume of the waste is (90bbl / 0.35), or 257bbl (Figure 2). The 10bbl drilling cuttings entering the system must be reduced to 4% using a solid phase volume concentration The new drilling fluid system has a solid phase volume concentration of 4% by 10bbl of new drilling cuttings, so the volume of the new drilling fluid is 250bbl. 250bbl drilling fluid consists of 240bbl clean drilling fluid and 10bbl drilling cuttings. The volume removed by the solid control equipment is 257bbl, which requires the drilling fluid tank to hold the diluent. Because 240bbl of clean drilling fluid is used to dilute 10bbl of cuttings, 7bbl needs to be added to maintain the level of the drilling fluid pool. This is basically a balanced system. There is no excess drilling fluid used to dilute drill cuttings, and it returns to the drilling fluid system. If the volume of waste and the volume used for dilution are exactly equal, the volume of the new drilling fluid is the smallest. To control the content of any target cuttings, the optimal cuttings removal efficiency can be calculated by a mathematical equation. The limiting condition of the equation is that the volume of waste and the volume of diluent are equal. The ratio of diluent required for each bbl cuttings is 2.57. Because the volume of the diluent that keeps the tank liquid level constant is larger than that of the drilling fluid diluted with 10bbl, the volume concentration of all cuttings in the drilling fluid system will be less than 4%.
The volume concentration of cuttings will be less than the target value of 4%. The volume of cuttings is initially 40bbl plus 10bbl remaining in the volume after using solid control equipment. The volume of the drilling fluid system was initially 1000bbl plus the volume of 257bbl of the new wellbore. It is about 1100bbl. The volume concentration of drill cuttings was 3.98%.
3.80% solid phase removal efficiency of solid control equipment
With 80% solid phase removal efficiency, 229bbl of cuttings and drilling fluid will be discharged by solid control equipment (Figure 3). Although the cuttings removal volume is only 20 bbl less than at 90% solids removal efficiency, the volume of the diluent used is much higher. After diluting 20bbl of cuttings retained in the system so that its concentration reaches 4%, you need to add 480bbl of diluent to the system. This 500bbl drilling fluid is composed of 20bbl drilling cuttings and 480bbl clean drilling fluid. The drilling fluid pool can only hold 229bbl volume, so 271bbl drilling fluid must be discarded. The total volume of waste is 229bbl drill cuttings and 271bbl drilling fluid removed by solid-phase equipment. The volume ratio of clean drilling fluid to drill cuttings needed to dilute 1bbl of cuttings is 4.8, and the volume of excess drilling fluid is 271bbl.
4. 70% solid phase removal efficiency of solid control equipment
With the solid control equipment removing 70% of the solid phase, removing 70bbl of cuttings requires removing 200bbl of fluid from the drilling fluid system, of which 70bbl of cuttings and 130bbl of drilling fluid (see Figure 4). Because 200bbl of fluid was removed from the drilling fluid system, the drilling fluid pool surface dropped. The 30bbl remaining in the system must be diluted to 4%. The new drilling fluid contains 4% of cuttings. 30bbl of cuttings must be diluted, so the volume of new drilling fluid is 750bbl. Therefore, 720bbl of clean drilling fluid must be added to the system. In a mud tank, only 200bbl of drilling fluid can be contained, so 520bbl of drilling fluid must be discarded or stored. The volume ratio of clean drilling fluid to cuttings required to dilute each 1bbl is 36/5, which is approximately 7.2, and the excess drilling fluid is 520bbl.
5. The amount of clean drilling fluid required to maintain 4% cuttings concentration
The volume of clean drilling fluid is an influential factor on the target drill cuttings concentration and the efficiency of solid phase removal.
The triangle line in Figure 5 indicates that the volume of clean drilling fluid used to dilute the cuttings is less than the volume of drilling fluid required to restore the drilling fluid pool level to its original position, and the target drillings volume concentration will decrease. The square dot line indicates that after the drilling fluid passes through the solid-phase equipment, the cuttings remaining in the drilling fluid need more clean drilling fluid to be diluted. The surface of the pool will rise a lot, and the drilling fluid beyond the surface of the pool must be removed from the system. The focus of the two lines indicates the minimum volume of diluent required to make the cuttings volume concentration 4% in the system.