Application in petroleum industry
Oil&Gas
Description
1. The application of inverters in the oil industry is crucial. The petrochemical industry plays a fundamental role in national economic development, but it also consumes a significant amount of energy. Its primary production processes rely on various pumps and air compressors. Currently, these devices are predominantly driven by constant-speed electric motors. By converting the majority of non-adjustable-speed motors to adjustable-speed operation and adjusting their power consumption based on load size, substantial energy savings can be achieved. The advancement of modern power electronics technology and AC speed control technology has revolutionized frequency range, dynamic response, precision requirements, and usage effects for AC motor variable-speed control.
1.1 The Application of Inverters in Nodding-type Oil Pumping Units
Nodding-type oil pumping units are widely used as the primary equipment for oil production due to their convenience, reliability, and cost-effectiveness. To minimize load fluctuations during the up-and-down stroke of the pumping unit, balance weights are typically installed. The motor load of the pumping unit exhibits periodic pulsations with instantaneous impacts. Notably, there are two peak values in the load curve corresponding to the "dead points" during each stroke. When restarting or free-parking, the pumping unit always starts from these dead points, requiring a substantial starting torque for its motor.
In order to ensure sufficient starting torque, it is common practice to design and select a pumping unit motor with greater capacity than required by actual loads. However, this approach introduces a new challenge: excessive pumping capacity can lead to reactive or empty pumping states that may result in well blowouts and gas locks – accidents that cause damage not only to drilling tools and pump units but also ground equipment. Moreover, continuous operation at excessive capacity increases mechanical wear and tear significantly, leading to high costs associated with traditional oil pumps along with issues such as loud noise and reduced operational reliability. Effective control of pump cavitation has become an urgent research topic given its detrimental effects on overall system performance. It is worth noting that oil pumps account for approximately 40% of total electricity consumption in oilfields – making them one of the largest energy consumers.
In recent years, there have been two primary types of direct energy-saving technologies available for oil pumps in the market. The first type involves the development of various energy-efficient motors specifically designed for oil pumps, such as super-high slip-torque motors, three-phase permanent magnet synchronous motors, high starting torque and dual stator structure motors, and variable-speed motors with electromagnetic speed regulation. However, due to the substantial investment required, it is still not feasible to completely replace conventional asynchronous motors with energy-saving ones in many oilfields. The second type entails the utilization of energy-saving distribution boxes that incorporate stator winding Y-Δ conversion voltage regulation and capacitor dynamic and static reactive power compensation. By altering the connection of the stator winding, it becomes possible to modify the motor voltage; however, this approach only allows for a fixed voltage output to be obtained by the motor and does not yield an ideal energy-saving effect. Although some devices employ bidirectional thyristors to achieve continuous voltage regulation of the stator voltage based on load conditions resulting in good energy savings effects; they also cause distorted power supply current waveforms leading to significant grid harmonic pollution issues making them unsuitable for large-scale long-term usage. On another note, employing variable-speed control can transform oil pump operations from inefficient prolonged running into a mode that matches actual well loads ensuring efficient extraction every time while reducing low-efficiency or ineffective extraction thereby lowering electricity costs and maintenance expenses while enhancing operational efficiency.
The heavy oil wells in a specific area of the Shengli Oilfield have successfully implemented variable-frequency speed control technology, resulting in a remarkable enhancement in pump efficiency. On average, daily oil production has increased by 2.1 tons, accompanied by an impressive electricity saving rate exceeding 30%. Additionally, the adjustable upstroke and downstroke speeds have effectively reduced labor intensity for workers.
The economic benefits analysis was conducted using the weighted average method for 15 wells, yielding the following annual per well benefits:
(1) Increased production and reduced electricity consumption costs: Production increase worth 504,000 yuan and electricity savings amounting to 61,000 yuan; totaling at 510.01 yuan.
(2) Investment expenses including equipment procurement and civil installation fees summing up to 943,000 yuan.
(3) Annual equipment maintenance and depreciation fees estimated at 136,000 yuan.
(4) Taxes paid annually reaching approximately 856,000 yuan.
(5) Profit generated annually equaling to 410.8 yuan.
(6) Payback period of investment calculated as investment divided by (profit + taxes), resulting in a payback period of only 70 days.
1.2 Application on submersible electric pumps
The production of submersible electric pumps (SEPs) has been widely adopted in oilfields as a highly efficient and easily managed mechanical production method. However, in complex faulty oilfields, the correspondence between oil and water wells is inadequate, leading to insufficient supply in some SEP wells, which negatively impacts their normal production and downhole unit lifespan. Taking an example from an oilfield production plant since 1997, approximately 30% of SEP wells have frequently experienced underloading due to insufficient supply, contributing to 45% of the total laydown rate caused by this issue. The average pumping cycle is only 66 days with an increased average annual maintenance cost per well amounting to 138,600 yuan. To extend the pumping cycle of SEP wells and ensure their normal production, the submerged electric pump variable-frequency control technology was introduced. By adjusting the frequency of power supply, it becomes possible to control the speed of submerged electric motors and adjust pump discharge volume accordingly. This ensures that the working characteristics of submersible pumps align with the oil well's production capacity while operating within optimal parameters for reducing mechanical and electrical faults. As a result, it extends the service life of SEP wells while increasing overall production output and energy savings.
The application of submersible electric pump inverters yielded highly significant results, specifically:
(1) The on-site commissioning success rate achieved a perfect score of 100%, and the measures proved to be highly effective with a success rate of 100% as well.
(2) The average power factor of the submersible wells significantly improved from 0.83 to an impressive 0.94.
(3) The average pumping cycle was extended by an impressive 207 days, increasing it from 66 days to a remarkable duration of 273 days.
(4) A total of 185 wells were successfully rescued from under-loading shutdowns, resulting in a reduction of shutdowns by an impressive amount equivalent to 235 tons of oil production. The average production efficiency of submersible wells experienced a substantial increase from 67.8% to an outstanding level of 98.1%. Additionally, a total number of 42 wells were saved from being laid down, leading to a reduction in oil production loss by an impressive amount equaling to 336 tons.
(5) The return on investment yielded exceptional results with a ratio standing at an impressive figure of 1:4.38.
2. Application of Inverters in Oil Drilling Machines
The drilling process is comprised of several key operations, including derrick raising and lowering, drilling, mud circulation, drill string replacement, casing installation, as well as logging. The primary equipment consists of winches, rotary tables, and mud pumps. The winch comprises a drum, gearbox, clutch, brake, motor and control equipment that are utilized for derrick elevation and descent purposes along with hoisting and lowering the drill pipe and casing. As the well depth increases, the length of the drill string also grows resulting in a rapid increase in weight; consequently imposing greater load on the winch. Currently there are oil wells reaching depths up to 7km with drill strings weighing nearly 600 tons in China. Given that the drill pipe needs to be raised or lowered approximately every 9m during operation; it follows that as well depth increases so does the time spent operating the winch which accounts for an increasingly larger proportion of total drilling time. In order to minimize costs it is preferable to spend less time in field or at sea; this necessitates high-speed operation capability from the winch ensuring smooth start-stop functionality thereby preventing damage to drilling equipment while improving well quality. Additionally good dynamic characteristics are required from driving equipment. If operations take place within an inland well field then power supply can be connected directly to its power grid whereby during drill pipe descent mode; energy generated by motor operation can be fed back into said grid leading to significant energy savings.
In Xinjiang province, a drilling company has installed Vekont's variable-frequency drive on a set of drilling equipment operating at a depth of 3200m. When updating and upgrading drilling equipment, it is recommended to adopt advanced variable-frequency drives, as they have significant potential for widespread implementation and will greatly contribute to the technological advancement of petroleum machinery industry in China.
Furthermore, due to space limitations, it is hard to list all the extensive applications of Vekont's variable-frequency drives in oil and gas gathering and transportation, oil and gas processing, treatment of oil-containing wastewater, water supply systems, drainage systems, and oilfield water injection systems.
