Multiphase pumps are finding added use as a supplement to conventional artificial lift systems to reduce the production footprint and environmental disturbance by combining oil and gas transport in a single multiphase pipeline to a central process facility. In tight shale production, the typical rapid decline of the natural reservoir pressure and added associated gas production demands solutions justifying increasing drilling, fracking, and completion costs.
The desire to extend ultimate recovery and leave minimum hydrocarbons behind requires a flexible multiphase pumping system that can deal with low reservoir pressures. At the same time, legislators in many regions, as well as public opinion, want reduced environmental impact from oil production and reduction of flaring and venting. When all these challenges are facing the operator, applying screw pump technology could be the best way forward.
With maturing reservoirs, the natural pressure declines, causing production to decrease without being able to overcome the backpressure of the gathering system. Multiphase pumps are able to draw down the flowing wellhead pressure while at the same time boosting the pressure and overcoming the downstream backpressure from flow lines, separators, etc.
The lower wellhead pressure transfers into lower bottom hole pressure, which improves the well inflow and the liquid level in the well. Downhole pumps will benefit as intake conditions improve, allowing uninterrupted operation above the bubble point, which adds to downhole pump uptime, total recovery, and shortens the production cycle. It also reduces wear and tear on sucker rod pumps and electric submersible pumps (ESPs).
Rather than separating the gas from liquids at the production site or pad, treating the liquids and compressing the gas, or sorting the liquids in stock tanks and flaring the gas, multiphase pumps can transport the untreated well flow in a single multiphase pipeline back to central processing.
Removing separators, heater treaters, flares, stock tanks, conventional pumps and compressors and replacing them with one piece of equipment – a multiphase pump system will result in significant savings. The economic returns are further improved by reducing truck transport of liquids. Gathering and monetizing associated gas production, which is often an undesired byproduct today, significantly improves well cluster development economics when it is possible to use centralized processing.
Twin-screw multiphase pumps deliver practically constant flow at a given speed independent of the gathering system backpressure. By changing the pump speed, the pumps can vary the flow rate and thereby control the pump inlet and the gathering pressure. Lowering the pressure can allow the opening of a pipeline prone to hydrate blockage, or make liquid logged wells flow again. Paraffin build-up and emulsions can be mitigated against and thus reduces the frequency of chemical injection and well treatment. The pump, which has low internal velocity will limit shearing and not aggravate oil/water emulsions, facilitating downstream treating.
Modern onshore and offshore topside multiphase pumps deliver flow rates of 4500,000 bpd (total inlet flow of oil, water and gas) at pressure boosts of up to 1500 psi. With the current trend moving towards new deepwater development and longer tie-backs, the industry has recently identified the need for subsea multiphase pumps capable of flows of up to 600,000 bpd and differential pressures exceeding 2500 psi. In addition, the longer step out distances require higher voltage power transmission, subsea power distribution, transformers and variable frequency drive (VFD) development. Onshore, the size of the multiphase pump installations increases as operators strive to centralize processing and production for savings in OPEX and to comply with stricter emission control regulations. In shale and tight formation production operators are reviewing options to move oils and gas to the market in pipelines instead of using trucks and rail tankers. Using multiphase flow lines will bring significant savings and will reduce exposure, making the process environmentally friendly. In addition, associated gas, which in some places is considered a nuisance byproduct, can be transported for use with a multiphase flow line.