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Using Artificial Lift to Enhance Oil Recovery
Priyanka Thamma, Technical Sales Engineer Artificial Lift, Schlumberger Growing energy demands and depleting natural resources around the world necessitate the use of various artificial lift techniques to enhance oil recovery. Any method that imparts energy to the fluid or reduces the opposing hydrostatic force to enhance the production or even enable wells that cannot flow naturally to flow is an artificial lift method.

If a well is producing 5000 bpd, then by installing a suitable artificial lift system the production could even go up to 7000 bpd. From Sucker Rod Pumps to Electrical Submersible Pumps (ESPs), the last century has seen a tremendous development in the technologies deployed in the field of Artificial Lift, enabling the operators to produce oil even in the most challenging environments. The artificial lift methods currently in vogue are beam pumps, jet pumps, Gaslift, progressive cavity pumps (PCPs), ESPs etc. The decision to choose the best artificial lift method is based on surface, reservoir, fluid and operational conditions.

With a long history, beam pumps are extensively used onshore to produce fluids at low flow rates. It converts the rotary mechanism of the motor on the surface to a vertical reciprocating motion to drive the pump shaft, thereby imparting a vertical movement to the fluid. On the other hand, PCP is a positive displacement pump employing a stator-rotor combination creating cavities that move from inlet to outlet creating the pumping action as the rotor is driven by the surface motor. Both these pumps are efficient in handling viscous fluids. The next variety of pumps i.e., Jet Pump uses the Bernoulliís principle and enables a high pressure source to boost the low pressure fluids. All these methods are limited by the flow rates and depths.

The most flexible and widely used artificial lift method is Gaslift. It can handle rates from 10 bpd to 80,000 bpd. In a typical gas lift application high pressure gas is injected into the casing-tubing annulus. The gas then enters the tubing through Gaslift valves to lighten the hydrostatic column and reduce the load on the formations thereby enabling the well to flow. One of the major advantages of gas lift lies in the flexibility of design, as the gas lift valves are all slickline retrievable. For example if the well conditions change over the life of the well such as water cut increase, the existing valves downhole can be retrieved and new valves (designed to the new conditions) can be installed using standard slickline methods thus eliminating the need for pulling out the completion. This in turn has proved to be cost effective over the long term due to minimal operating costs to maintain the gas lift system.

Nowadays, the conventional operating orifice valves are being replaced by NOVA series orifice venturi operating valves that have an exclusive computer-generated flow profile to promote a constant flow gas-injection rate. Its design maximizes efficiency, reduces costs, and improves productivity. A major operator in Egypt, seeking to improve their Gaslift operation, installed NOVA valves. The first NOVA valve installation resulted in a decrease in casing injection pressure (from 85 bars to 75 bars) and a dramatic reduction in pressure surges (from 6-18 bars to 7-9 bars). The optimum gas injection rate was achieved, resulting in stable production and better utilisation of the gas available for injection. Latest developments in Gaslift technology required to address the higher operating envelopes as client requirements demanded increased performance and reliable gas lift systems.

The barrier mandrel and barrier valve were developed recently to address those requirements. The barrier valve effectively ensures zero communication between tubing to casing annulus by increasing reliability of sealing elements and the barrier mandrel is a patented dual pocket technology that offers the client complete assurance of casing to tubing integrity at all stages during the life of the well. The available Gaslift Products cater to a wide range of H2S and CO2 downhole conditions, ranging from its metallurgy (standard steels to Inconel925 & Incoloy718) and range of mandrels suited for gaslift, waterflood and chemical injection applications.

Gaslift technology today has come a long way from when it was first implemented 60 years ago. Changes in the product design offering have ensured that Gaslift is not limited by packer depth but can be injected below a packer to pass gas to a long perforation interval (PerfLift Technology), in addition to meeting demands for a extreme high pressure, subsea applications (XLift) and not to mention SensaLine (slickline with Fiber Optics) for real-time visual action of all gas lift valves, problem identification & immediate rectification and ability to monitor simultaneously the Reservoir and Gaslift valves.

Another lift system that is capable of handling huge volumes (upto 90,000 blpd) and from great depths is an ESP system. ESPs can operate in high angle and horizontal wells. Generally ESPs are considered to be the most efficient and economic lift method for high flow rates. Variable Speed Drives can widen the operating range of the ESP allowing the lift system to adapt to the changing reservoir conditions. Contrary to the myth that ESPs cannot handle sand, gas etc, todayís ESP technologies have performed outstandingly well in abrasive as well as gassy environments. Development of abrasion resistant zirconia bearings with a shaft-bearing design that withstands the rigors of the oilfield has enhanced the run life of ESPs in abrasive environments.

Advancements in gas handling technologies put forth equipment like Poseidon (a multiphase, axial flow gas-handling device) that enables the ESP to handle upto 70 per cent free gas without any gas-locking issues. The Poseidon system can increase production and extend the use of ESPs in oil wells with high gas cut in which production is limited by the centrifugal pumpís ability to handle gas. This technology has enabled the operators working with high volumes of gas to increase the drawdown and operate the pump effectively at lower intake pressures resulting in enhancement of production.

To recover heavy oil reserves, thermal methods have proven to be efficient in some parts of the world. A reliable artificial lift system is a key to the success of such a project. In line with the needs of the industry, ESPs that can work at bottomhole temperatures as high as 425 deg F have been designed. In Canada, REDA Hotline pumps are increasing oil production from Steam Assisted Gravity Drainage (SAGD) recovery operations. Installed to replace beam pumps in one SAGD field, these ESPs are averaging 4,400 bbl/d [700 m3/d], or 55% more oil than the original pumps. In this field, run lives exceeding 900 days are proof of exceptional engineering and reliability.
The ESPs can be connected in series or parallel configurations using Y-tools and POD systems giving the operator the power and reliability demanded in highrisk, high-cost producing wells. In series, the two ESP systems work together to provide double the lift or horsepower. The lower system in the well charges the upper system and produces a high volume of fluid at a greater distance. Essentially, the system is used to provide a greater drawdown, thus increasing the production from deep or remote wells.

Parallel systems can virtually eliminate the cost of deferred production caused by workover rig delays or scheduling. They provide reliable in-well backup systems when the performance of the initial ESP systems declines or ceases. The systems can be configured to automatically switch from one system to another without slickline or human intervention. With automation, production losses are effectively eliminated.

To enable a rigless deployment and a faster and safer retrieval, ESPs can also be run using coil tubing units (REDACoil). Here, the fluid is produced through the annulus and the power cable is protected inside the coil tubing. Efforts are now being put into developing a cable deployed ESP systems that will considerably reduce the workover time.

The key for a lift system to have a longer run life, lower operating costs and fewer early failures and also for increased production and ultimate recovery is to monitor the performance of the well and take proactive actions. Hence it is extremely important to have a gauge downhole that transmits the downhole pressure and temperature data which can be used to monitor, trend, protect, validate & analyze and use the analysis results for optimisation. Variable speed control for ESPs can be based on direct downhole readings. The downhole lift system can be protected by setting alarms and trips that are based on downhole sensor readings. Real time surveillance can help monitor early warnings to avoid tripping and prevent adverse events. Causes of alarms can be identified through real time diagnostics and recommendations can be sent to field personnel in real time.

More than half of all artificially lifted wells offer potential for production optimisation. On average, oil production improves by 20 per cent as a result of the optimisation process. A powerful optimisation package can be achieved by putting together a reliable and efficient pump technology, advanced diagnostic tools and Data consulting services expertise by which Inflow and Outflow analysis can be performed to find out every opportunity to produce that extra barrel of oil or to avoid deferred production, leading to ultimate recovery.