Oilwell Cementing Unit

Overview

An oilwell Oilwell Cementing Unit is the surface equipment that places cement around the casing of an oil or gas well. After a section of casing is run into the borehole, cement slurry is pumped down inside the casing and back up the annulus between the casing and the rock. When it sets, the cement seals the annulus, supports the casing string, and isolates the producing zone from water-bearing formations above and below it. The unit performs three jobs in sequence during a single operation: it blends dry cement powder with water to a specified density, it pumps that slurry at high pressure into the well, and it records the density, pump rate, and pressure so the operator can confirm the slurry placed correctly.

The complete unit is built around two Triplex Plunger Pump assemblies driven by a single diesel Diesel Power Pack. A Recirculating Mixing System prepares the slurry, a pair of Displacement Tanks measures the volume pumped, and a high-pressure HP Discharge Manifold routes the slurry to the wellhead. The whole assembly sits on a Skid Frame that mounts to a truck chassis or a stationary skid.

High-Pressure Pumps

The core of the unit is the Triplex Plunger Pump, a positive-displacement pump with three plungers that deliver slurry against well pressures as high as 15,000 psi. Each pump is split into two halves. The Fluid End is the wetted section: a forged Fluid End Block holds three Pump Plunger bores, each served by a Suction Valve and a Discharge Valve seated on a Valve Seat and held closed by a Valve Spring. A Plunger Packing Stack seals each plunger against the block. Cement slurry is abrasive, so the plungers, valves, and seats are surface-hardened wear items replaced on a regular schedule.

The Power End converts rotation into reciprocating motion. A Crankshaft running on a Ball Bearing set drives three Connecting Rod links, each pushing a Crosshead and a Pony Rod that connects to a plunger. The crankcase is pressure-lubricated by a Crankcase Lube Pump, with an Oil Seal at each rod opening to keep oil in and slurry out.

Power and Drive

Mechanical power comes from the Diesel Engine, a turbocharged six-cylinder unit producing roughly 600 hp. It uses a cast Engine Block, six Piston Assembly sets, a forged Engine Crankshaft, and six Fuel Injector units managed by a Engine Control Unit. A Turbocharger raises charge density for the high power output. Engine output passes through a Transmission, a multi-speed gearbox that uses a Helical Gear Pair set and a Hydraulic Clutch Pack to step engine speed down to the pump shaft speed required for a given rate and pressure. A Drive Shaft couples the transmission to each triplex pump. A Engine Radiator cools the engine and a Fuel Tank feeds it through an Engine Air Filter.

Mixing the Slurry

Slurry is blended in the Recirculating Mixing System using the recirculating jet method. Water enters the Jet/Venturi Mixer, where it passes through a Venturi Throat and a Mixing Nozzle. The high-velocity jet draws dry cement from the Cement Hopper and entrains it into the stream. The throat and nozzle are lined with tungsten carbide because the cement-water mix erodes ordinary steel quickly. The mixed slurry drops into the Mixing Tub, where a Tub Agitator keeps solids in suspension. A Centrifugal Recirc Pump, a centrifugal pump built on a Stator Assembly and Rotor Assembly with a Pump Impeller in a Pump Volute, continuously recirculates slurry between the tub and the mixer. Recirculation lets the operator trim density by adding water or cement until the densitometer reads the target value before the slurry is sent downhole. A Mechanical Seal keeps slurry off the pump bearings.

Delivery and Measurement

Slurry leaves the triplex pumps through the HP Discharge Manifold, built from a forged Manifold Block, several HP Plug Valve units, and articulated Chiksan Swivel Joint joints. The swivels and Treating Iron Pup Joint sections, joined by Hammer Union connections, make up the treating iron that carries slurry to the wellhead while allowing the rig-up to flex. A Pressure Relief Valve and a Pressure Sensor protect the line against overpressure. Volume is tracked by the Displacement Tanks, a pair of calibrated Measuring Tank vessels read through a Sight Gauge. Clean displacement fluid drawn from these tanks pushes the slurry out of the casing and into the annulus at the end of the job. Water and chemicals come from the Water & Additive System, where a Water Charge Pump supplies the mixer and two Additive Metering Pump units meter liquid additives.

Instrumentation and Control

The Instrumentation & Data System system records the job. A Densitometer continuously measures slurry density, two Slurry Flow Meter units track rate, and several Pressure Sensor units watch line pressure. Their signals feed a Data Acquisition Board that logs the full job. The operator works from the Control Cabin, where the Operator Console drives engine throttle and pump rate, and two LCD Panel displays show density, rate, and pressure in real time.

Variants and Use

Units are configured as truck-mounted for land work or as skids for offshore platforms and barges. Single-pump units handle small casing jobs, while twin-pump units like this one support higher rates and provide redundancy for critical cement placements. Pressure ratings of 10,000 psi cover most shallow and intermediate casing strings, while 15,000 psi units are used on deep wells and high-pressure formations. The same unit also performs squeeze cementing to repair leaks and plug-and-abandon work to seal wells permanently at the end of their life.