Slurry density meter · PS7000

On-line Cement Slurry Density Measurement in Oil-Well Cementing

Oil-well cementing slurry

Cementing operators struggled with real-time density control in narrow-pressure-window wells due to inaccurate Coriolis and hazardous radioactive meters. The PS7000 online slurry density meter delivers stable, accurate 1.0–3.0 g/cm³ measurement during on-the-fly mixing, enabling reliable automatic density control.

Applicable industries
Tunnel Boring (TBM)
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On-line Cement Slurry Density Measurement in Oil-Well Cementing

On-line Cement Slurry Density Measurement in Oil-Well Cementing

1. Process Background

Cementing is a critical operation in oil & gas drilling and completion: cement slurry is pumped through the cementing pump into the annulus between casing and formation, where it sets into a cement sheath that isolates oil/gas/water zones, supports and protects the casing, and safeguards long-term wellbore integrity. Cement-slurry density is the single most important real-time control parameter of a cementing job — it must fall precisely within the “safe density window” between formation pore pressure and fracture pressure. If the density is too low, the annular hydrostatic column is insufficient, risking formation-fluid influx or even a blowout, with weak set cement and poor zonal isolation; if too high, it exceeds the formation fracture pressure, causing lost circulation, slurry losses and channeling, and a failed cementing job. In deep, ultra-deep and HPHT wells with narrow pressure windows, the allowable density margin is often only 0.02–0.05 g/cm³.

Modern cementing increasingly relies on continuous on-the-fly mixing by cementing units (skids/trucks): cement powder and water are blended on-line in proportion, and the density fluctuates in real time throughout mixing. “One-button” automatic mixing — in which the control system adjusts the water/cement ratio automatically to a target density — depends entirely on an on-line instrument that measures slurry density in real time, accurately and stably; once the density reading is distorted, automatic control becomes impossible and operators must fall back on manual experience. The growing use of ultra-low-density (anti-loss) and weighted (high-pressure-formation) slurries further demands a density meter with a wide 1.0–3.0 g/cm³ range.

2. Pain Points of Conventional Density Measurement

• Radioactive-isotope (gamma-ray) density meters: reasonably accurate, but the built-in radioactive source is a regulated radiation device requiring a Radiation Safety License; during cross-region redeployment of cementing units and on offshore platforms, transport, storage and decommissioning of the source are strictly controlled, with high purchase and annual-maintenance costs and significant safety/environmental risk.

• Coriolis (bent-tube) mass-flow density meters: the current mainstream choice on cementing units, but they show large errors on low-density slurry and on the gas–liquid two-phase (bubbly) medium produced during mixing, preventing the “one-button” cementing unit from running under automatic remote control; the tube is also prone to wall caking and scaling, after which the whole meter fails and parts/maintenance costs are high.

• Tuning-fork / vibrating density meters: maximum working pressure is typically only 10 MPa (20 MPa for special versions), inadequate for the high-pressure manifold of cementing pumping; performance is mediocre on crystallizing, scaling media.

• Differential-pressure density meters: affected by the cementing-unit structure and by uneven up-and-down slurry surging during mixing, the reading drifts; diaphragm life is short under high pressure and severe abrasion.

• Manual pressurized mud balance: relies on periodic manual sampling — data is delayed and discrete and cannot participate in closed-loop control.

3. The PS7000 Solution

The PS7000 measures by the ultrasonic acoustic-impedance method: two transducer probes are welded onto flats milled on opposite sides of the pipe; the ultrasound is emitted from outside the pipe wall and the acoustic-impedance signature of the returning echo is analysed to derive density — never contacting the cement slurry. Because the probes do not intrude into the bore and the pipe wall itself is the pressure boundary, the high-pressure version withstands cementing-pump and wellhead pressures (HP version rated 150 MPa), fundamentally unlike wetted instruments such as tuning forks and differential-pressure cells. Combined with the Chirp wide-band analysis algorithm, it delivers a stable output even on the gas–liquid two-phase, bubbly and low-density slurry during mixing, solving the core “inaccurate, jumping readings” problem of Coriolis and tuning-fork meters.

Typical deployment: the PS7000 is installed on the mixing-return / high-pressure manifold line of the cementing unit (skid), outputting real-time slurry density at process conditions; via dual 4-20 mA and RS485 Modbus it feeds the cementing-unit control system to support closed-loop water/cement-ratio control for “one-button” automatic mixing. The same meter can also monitor spacer- and flush-fluid density. The range covers 1.0–3.0 g/cm³, response time is < 1 s, and the reading is verified to be independent of flow velocity (3–15 m/s).

On-line Cement Slurry Density Measurement in Oil-Well Cementing

Figure 1 Process layout for on-line cement-slurry density measurement in continuous-mix oilfield cementing

Core value of the PS7000 in oil-well cementing

▸ Chirp wide-band anti-bubble algorithm — stable output on two-phase, bubbly and low-density slurry, ending the “inaccurate / jumping” readings of Coriolis and tuning-fork meters;

▸ Probes welded to the pipe exterior, no intrusion into the bore — the pipe wall is the pressure boundary; HP version withstands 150 MPa cementing-pump / wellhead pressure;

▸ Non-contact · no wall caking, no clogging — no cleaning, no zero drift; ends the bent-tube meter’s caking shutdowns and high upkeep;

▸ Range 1.0–3.0 g/cm³, covering ultra-low-density (anti-loss) to weighted slurry; identical reading across 3–15 m/s flow;

▸ Completely non-nuclear · zero radiation — no Radiation Safety License for cross-region redeployment or offshore work;

▸ < 1 s response + dual 4-20 mA / RS485 Modbus — seamlessly supports “one-button” automatic-mixing closed-loop control.

4. Customer Value

The PS7000 acoustic-impedance density meter has passed a dedicated cement-slurry density test at the cementing institute of a leading national petroleum-engineering technology research institute: five slurries at 1.3, 1.6, 1.9, 2.3 and 2.5 g/cm³ were measured continuously at three flow velocities (3, 9 and 15 m/s) and compared point-by-point against a manual balance densitometer. The instrument readings agreed closely with the weighing method (deviation ≈ ±0.02–0.03 g/cm³) and were unaffected by flow velocity, confirming the feasibility and accuracy of high-pressure cementing-fluid density measurement.

Dimension

Conventional (nuclear / Coriolis / tuning-fork)

PS7000 solution

Operational safety

Radioactive-source control · license required

Intrinsically safe · non-nuclear, zero radiation

Bubble / low-density measurement

Large two-phase error · jumping data

Chirp anti-bubble · stable at low density

High-pressure capability

Tuning fork ≤ 20 MPa · limited

Pipe-wall pressure boundary · HP up to 150 MPa

Wall caking / clogging

Bent-tube caking shutdown · high upkeep

Non-contact · no caking, no clogging

Automatic-mixing control

Inaccurate · hard to close the loop

< 1 s response · supports “one-button” loop

At a cementing-equipment manufacturer and operating site in Southwest China, the PS7000 was deployed on the cementing-unit mixing line; in repeated comparisons against manual sampling and laboratory analysis it has maintained stable long-term accuracy. For offshore high-pressure cementing, a wellhead high-pressure PS7000 variant is also being trial-produced and applied. The combination of non-nuclear operation, high-pressure tolerance and bubble immunity makes the PS7000 the ideal choice for on-line cement-slurry density measurement and “one-button” automatic mixing.

More applications for Slurry density meter

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Online Measurement of Gypsum Slurry Density in Absorption Towers

In the wet flue-gas desulfurization process, real-time monitoring of gypsum slurry concentration is crucial for ensuring the quality of the by-product gypsum and the proper operation of equipment. However, conventional concentration meters—such as mass flow meters, tuning fork sensors, and differential pressure concentration meters—suffer from issues like radiation safety concerns, bubble interference, and scaling. Pisonics’ PS7000 employs ultrasonic technology for non-contact measurement, can penetrate bubble layers to deliver stable and reliable concentration data, and requires no maintenance, with a service life exceeding five years.

Online Density Measurement for Limestone Slurry Preparation

During the preparation of limestone slurry, conventional density-measurement solutions suffer from issues such as wear and scaling, leading to inaccurate data and compromising flue-gas desulfurization efficiency. The PS7000 acoustic impedance concentration meter overcomes these challenges through non-contact ultrasonic measurement, delivering stable, high-precision online density monitoring and ensuring consistent control of slurry concentration.

Online Measurement of Desulfurization Wastewater Density

In the flue-gas desulfurization process at power plants, online monitoring of the slurry density in the underflow from the thickener is critical. Conventional contact-type instruments are prone to scaling and corrosion, making it difficult to meet the demands of long-term, stable operation. Pisonics’ PS7000 acoustic impedance concentration meter employs a non-contact ceramic probe and a corrosion-resistant lining, effectively addressing severe corrosion and fouling while ensuring the accuracy and stability of the measurement data.

Online Density Measurement for the AFT Tower (High-Concentration Desulfurization Slurry Processing Tower)

In the AFT tower, measuring the density of high-concentration, high-viscosity, and easily crystallizing slurries has long been a challenge. The PS7000 acoustic impedance concentration meter, employing non-contact measurement, overcomes the failures of conventional instruments caused by clogging, wear, and crystallization, enabling real-time, continuous monitoring of slurry density and automated control of the discharge process, thereby ensuring stable system operation.

Selection support

Guides

Comparisons

Voices from users of this product

"Our original tuning fork and differential pressure meters on the absorber gypsum discharge main had recurring problems with bubbles and scaling — we had to shut down weekly to clean them. After switching to PS7000, both problems disappeared. Basically maintenance-free now, accuracy is stable, and it fully meets our FGD process control needs."

Thermal Control Foreman Wang
Thermal Control Specialist
A certain thermal power plant in Inner Mongolia

"After switching to the PS7000, our overflow density readings finally stabilized — we stopped tuning reagent dosing by feel. The unexpected win was not having to clean the sensor weekly; our previous radiometric meter needed window-wiping almost daily in the scaling slurry."

Director Li
Mineral Processing Workshop Director
A certain copper mining enterprise

"Our potash blending tank is a harsh environment — KCl near saturation, 30~40% crystal content, temperature swinging 5~20°C. Traditional density meters can't hold up here. After two weeks of PS7000 service, the deviation from manual lab samples stayed in the 0.5~0.8% range, even during concentration peaks. No anomalies."

Director Xie
Process Engineer
A potash fertilizer plant in Qinghai

FAQ

How is dredge production (dry solids per hour) measured?
You cannot get it from density alone. Dry-solids production P_dry (t/h) = Q x Cv x rho_s, where Q is the volumetric flow (from a flow meter), Cv = (rho_m - rho_w)/(rho_s - rho_w) is the volumetric concentration from the mixture density rho_m (from an inline density meter such as the PS7000), and rho_s is the dry-solids density. The Pisonics Dredge Production Monitor reads the density and flow meters over Modbus and computes this every second, with dashboard and shift totals. See /guides/dredge-production-calculation-density-flow.

Can I measure dredge slurry density without a radioactive source?
Yes. An ultrasonic acoustic-impedance meter (PS7000) reads discharge-line slurry density to +/-0.005 g/cm3 with no radioactive source, so there is no shipboard radiation licence, no port-inspection delay and no radiation-safety officer. A clamp-on option (PS7010) allows no-hot-work retrofit. See /guides/non-nuclear-density-meter-for-dredgers.

What density meter should go on a cutter-suction dredger discharge line?
A PS7000 ultrasonic acoustic-impedance meter suits CSD discharge lines (DN50-DN1000): flush sapphire window for abrasion, Chirp wideband to reject entrained air, non-nuclear. For no-cut retrofit use the clamp-on PS7010. Pair with a flow meter and the Dredge Production Monitor to also get dry-solids t/h. See /industries/dredging.

Is the PS7000 ultrasonic density meter a radiometric device? Does it need a radiation license?

The PS7000 is an acoustic-impedance ultrasonic density meter with no radioactive source whatsoever. No radiation license is required. It uses only piezoelectric transducers to send and receive ultrasonic signals — the same physical principle as medical and NDT ultrasound.

If you're currently using a Cs-137 / Co-60 source-based meter and want to remove the regulatory burden, PS7000 is a drop-in alternative. We also offer the PS7500 gamma meter, which uses an exempt-activity Na-22 source (< 1000 KBq) — also requires no radiation license.

Can an ultrasonic concentration meter measure mine backfill slurry?
Yes. Ultrasonic acoustic-impedance meters (PS7000) are well suited to online concentration/density of high-solids, abrasive mine backfill (tailings / paste-fill) slurry: the flush sapphire window resists wear with no protruding parts, and Chirp wideband processing rejects entrained-air scatter. It is a non-nuclear alternative to Cs-137 gauges — see /industries/mining.

Can PS7000 really measure stably in bubbly mining slurries?

Yes.

The PS7000 employs a linear frequency-modulated (Chirp) acoustic impedance algorithm—after transmitting a broadband ultrasonic pulse, the host unit analyzes the echo signal in the frequency domain, and multiple-reflection interference caused by bubbles is identified and eliminated by the algorithm. This is the core difference between the PS7000 and conventional reflective ultrasonic density meters: traditional single-frequency reflection is highly sensitive to bubbles, whereas the PS7000’s Chirp algorithm is virtually immune to them.

At the gypsum discharge line of an absorption tower in a thermal power plant in Inner Mongolia (under conditions of continuous air oxidation that generate dense bubbles), the PS7000 has been operating stably for several years after replacing the original tuning fork concentration meter.

What installation requirements does the PS7000 have?

The installation requirements for the PS7000 flanged direct-insertion type are as follows:

  1. Straight-run pipe sections: ≥5D (upstream) + 2D (downstream), where D is the nominal pipe diameter;
  2. The installation point must operate with a full pipe to avoid stratification of gas and liquid phases;
  3. The applicable pipe sizes range from DN50 to DN1000 (larger sizes can be customized);
  4. The flanges are compatible with ANSI/DIN/JIS standards;
  5. In highly abrasive conditions, it is recommended to use a 316L probe with special ceramics or a 2205 duplex stainless steel probe;
  6. In strongly corrosive environments, a PTFE-lined option is available.

If the pipeline does not allow for tapping, please consider the PS7010 clamp-on type instead.

PS7000 vs nuclear density gauges: which costs less over the life cycle?

On purchase price alone, ultrasonic and nuclear gauges sit in a similar bracket. The gap opens over 5 to 10 years of ownership.

Hidden cost list of a Cs-137 / Co-60 nuclear gauge:

  • Radiation safety licensing and annual reviews, plus operator training and certification;
  • Licensed transport and installation filing for the source;
  • Dose monitoring and record keeping during service;
  • Source replacement as activity decays (purchase, transport, commissioning, return of the old source);
  • End-of-life disposal of the spent source — often the single largest bill.

PS7000 acoustic-impedance ultrasonic gauge: no radioactive source and no permits of any kind; non-contact sensor with zero wear and zero clogging, sensor life of 5 years or more, virtually maintenance free with no consumables. Power plant, potash and iron ore sites have run 2+ years at near zero maintenance.

Bottom line: on a 5-year basis the total cost of ownership of the PS7000 is typically far below a nuclear gauge. Where a nuclear principle is genuinely required (such as dense-medium coal washing), the PS7500 with an exempt-activity Na-22 source needs no license, though the roughly 2.6-year half-life still implies periodic source renewal.