Production from wells, in the oil and gas industry, often contain particulates such as sand. These particulates could be part of the formation from which the hydrocarbon is being produced, introduced particulates from hydraulic fracturing or fluid loss material from drilling mud or fracturing fluids, or from a phase change of produced hydrocarbons caused by changing conditions at the wellbore (asphalt or wax formation). As the particulates are produced at surface the particulates can cause erosion and plugging of production equipment. In a typical startup, after stimulating a well by fracturing, the stimulated well may produce sand until the well has stabilized, often up to several months after production commences.
Erosion of the production equipment is severe enough to cause catastrophic failure. High fluid stream velocities are typical and are even purposefully designed for elutriating particles up the well and to the surface. An erosive failure of this nature can become a serious safety and environmental issue for the well operator. A failure, such as a breach of high pressure piping or equipment, releases uncontrolled high velocity flow of fluid which is hazardous to service personnel. Release to the environment is damaging to the environment resulting in expensive cleanup and loss of production. Repair costs are also high.
In all cases, retention of particulates contaminates surface equipment and the produced fluids, and impairs the normal operation of the oil and gas gathering systems and process facilities.
To protect wellsite production equipment, desanding equipment is often employed upstream of the production equipment for a period of time depending on the extent of sand production. The desanding equipment usually operates at well pressures and the vessels are manufactured as pressure vessels. Such desanding equipment typically collects sand until a reserve storage capacity has been reached, after which the desanding equipment should be emptied of accumulated or collected sand for optimal performance.
Methods to remove sand includes opening of a ‘quick closure’ to an off-line vessel and personnel manually remove the collected sand. The manual approach is common in lower pressure horizontal gravity or filtration based vessels. Quick closures are typically specified for ANSI/ASME 2500 applications, or up to about 6000 psig at conventional operational temperature ranges. This method requires depressurizing the equipment and opening the closure to gain entry to the vessel. This may expose personnel and the environment to toxic wellbore gases. Other on-the-fly configurations utilize an unloading valve that can be opened while the vessel is under operating pressure. The stored energy in the vessel is used to forcibly evacuate the sand and any associated liquids collected therewith, through the unloading valve. This method is more common in vertical or spherical vessels with a sump. This method exposes the unloading components to the erosive effects of the sand in a high pressure drop situation. Aside from high repair costs associated with this method, personnel and the environment can again be exposed to the discharging wellbore gases with the expelled sand. Further, erosive failure of the unloading process can cause a breach in the valve or associated connective piping at potentially lethal pressures and velocities.
With reference to FIG. 1, as demonstrated in Canadian Patent 2,433,741, issued Feb. 3, 2004 and in Canadian Patent 2,407,554, issued Jun. 20, 2006, both to Applicant, desanding equipment 10 having an elongate, horizontal pressure vessel 11 is disclosed for sand separation having an inlet 24 at one end and an outlet 16 at another, the outlet separated from the inlet by a downcomer flow barrier 14, such as a weir, adjacent the vessel's outlet or exit. Water L and sand S accumulate in an accumulation zone 15 along a belly portion of the vessel 11. Pressure appropriate, a quick closure 52 can be provided at a discharge end 42 of the vessel. Sand S accumulates along a substantial length of the bottom of the elongate vessel. The length of the vessel increases the difficulty of periodic manual removal, typically performed through the quick closure 52 using long-handled scraper rods and the like.
With reference to FIG. 2, in U.S. Pat. No. 8,945,256, issued Feb. 3, 2015, also to Applicant, another sand separator 20 having a sand separator vessel 22 is disclosed, similar to the above, but being tilted at a non-zero inclination angle α. Again, entrained liquids L and sand S collect in an accumulation zone 15 in the belly portion of the vessel 22. Even at low angles, the heavy door of quick closures can be difficult to handle. At high inclination angles, approaching the angle of repose of the collected sand S, the door is too heavy to lift, and operation of a quick closure is exacerbated as the sand S will accumulate against the closure. Further, the sand S can self-discharge unpredictably through the closure when opened. In other instances, higher pressure vessels rated to ANSI/ASME 2500 and up, are often precluded from using such fittings.
When manual removal is unacceptable, and pressure restrictions preclude quick closures, manufacturers have turned to permanent fittings and an unloading valve adjacent the bottom of the vessel for pressurized ejection of sand therethrough.
With reference to FIG. 3, in U.S. Pat. No. 9,759,057, issued Sep. 12, 2017, to Dynacorp Fabricators, Inc., a double-tube sand separator 30 is disclosed using both unloading valves and backup manual removal. A first lower horizontal tube 33 is coupled to a second upper horizontal tube 64 by a bridging conduit 62. The sand separator removes particulates in three steps: gravity knock-out in the lower tube 33; a screen across the bridging conduit 62 between the upper tube; and a tubular filter in the upper tube. Sand accumulates over time in an accumulation zone in the belly portion of the lower tube 33. For clean out purposes lower tube 33 includes two unloading ports 82 spaced along its bottom surface and a quick release closure 52 at the closure or discharge end 42. Sand-laden fluid F flows from one end 12 of the lower tube to the discharge end 42, up the bridging conduit 62 and back along the filter of the upper tube 64. To remove sand, the inlet 24 and outlet 16 of the separator 30 are shut in, trapping process pressure therein. Unloading valves are then opened and process pressure blows down sand and water from vessel 33 to a blowdown vessel. Once the vessel has been blown down, the unloading valves are closed and the vessel re-connected to the process. The energy of the trapped process pressure in the vessel is limited and may not fully remove all the accumulated sand. Accordingly, the operator opens the quick closure 52 in any event to manually clean out the vessel with a scraper tool.
With reference to FIG. 4, in U.S. Pat. No. 7,785,400, issued Aug. 31, 2010, to Sand Separators LLC, a spherical sand separator 40 having a spherical vessel 44 is disclosed having lateral inlet 24 and a top vertical outlet 16. Sand accumulates in an accumulation zone at a bottom 142 of the vessel. Sand is periodically removed through a drain port 82 and unloading valve The vessel remains on-line and is an example of the risks of sand removal at process pressures to both equipment and personnel.
As shown in FIGS. 5A and 5B, in U.S. Patent Publication 2016/0082377, published Mar. 24, 2016, to Applicant a vertical sand separator 50 is disclosed having a vertical vessel 55 with an inlet 24 at the top of the vessel and a top or lateral outlet 16 separated by a phase baffle. Sand separated from fluid flowing through the vessel accumulates at a bottom 142 of the vessel. The vessel has a drain port 82 at the bottom surface coupled to a double isolation unloading valve or the like for sand removal. The vessel remains on-line and is an example of the risks of sand removal at process pressures to both equipment and personnel.
The periodic removal of the accumulated particulates from the sand separator is a slow and labor-intensive manual process, or alternatively unloading under pressure is known to be abusive to the equipment and poses a risk to personnel. As such, there has been a desire to improve the ease and speed with which the vessel can be cleaned while also being mindful of its structural integrity.