DeSander and Separator sand level realtime monitoring for automatic removal

The ability to monitor the level of sand in desanders, separators, and flowback systems allows for automation and higher efficiency of sand removal processes and improved usage and lifetime of equipment.

Introduction

Sand production is one of the major concerns in the Oil and Gas Industry. The sand is created from the fluids and rocks extracted from wells. As a consequence of sand presence, the overall transport and transformation process is affected by deterioration in equipment (wellbore, pipelines, tubing, valves, choke, separator), production stops, decrease in production rate, early maintenance, etc. High economic efforts are therefore put into sand management and control in the field.

Sand production is an issue present on the Upstream side of Oil and Gas, which deals with the exploration, extraction, and production of crude oil and gas. After a well is drilled and vetted with economically extractable quantity of hydrocarbons, wellheads are used to control the extraction rate and conditions. Single or multiphase separators are then used to obtain the hydrocarbons needed for refining or processing, which is known as the Downstream side of the industry.

This article describes the Rheonics Sand Detection SDP sensor and how it is used to monitor the sand level in the sand separation equipment, allowing quick actions for better sand management.

Rheonics sensors are also used for mud weight monitoring of drilling fluids in realtime on rig sites.

Figure 1: Oil and Gas extraction and sand production overview

Sand Managament level monitoring and control

Sand Management relates to the “Sand life cycle”, which includes procedures such as initial modelled predictions, actual monitoring, and final disposal of sand accumulation, considering the environmental, safety, and economic aspects.

During sand management required actions are: separation, collection, cleaning, measurement, and monitoring.

Sand Separators

Separation is a process used to isolate solids from liquid contained in the multiphase fluid coming from the well. Equipment used for sand separation, aka. Desanders, can be gravity vessels (i.e., free water knockout (FWKO) with a sand jet), sand trap desanding, hydro cyclone, or filter systems.

These desanders vary in designs, sizes, and working principles. The selection depends on the required capacity, flow rate, solids size, location in the production line, economic impact, etc. There are different stlye of desanders suited for specific use case like multi-liner desander, insert desander, etc.

Wellhead desander are multiphase soild-fluid cyclone separators designed to treat full wellstream flow. They can work with mixed oil, gas, water streams and can operate at full gas void fractions and are used in both gas and oil wells. They are used for both handling temporary solids production during well testing and clean-up as well as for permanent ongoing sand production processing. They are built to meet ASME and API-6A design ratings.

The next figure shows common desanders used in different locations and where inline Rheonics sensors can be used.

Figure 2: Desander types and locations in upstream oil and gas processes

Installation of a desander can be defined by its location related to the choke valve. Choke valves are used to control the flow rate and pressure in the line. Desanders located before the choke or at the wellhead, protect all equipment downstream (including the wellhead choke) but require high-pressure design. Desanders located after the choke require much lower pressure ratings, may be cheaper, but will not protect the choke (maintenance or replacement required), and are usually bigger in dimensions.

An additional advantage of desanders installed before the wellhead choke is that the filtered sand is usually cleaner, with a low percentage of hydrocarbons (up to 0.5% of concentration by weight – kg oil per kg dry sand) [5].

Hydrocyclones:

A cyclonic separator device, also called “desanders”, “desanding cyclone“ or “desanding hydrocyclone“, uses a swirling flow with the effluent multi-phase fluid to capture and separate solids. The centrifugal forces force solids, like sand, to move near the wall and are pulled down by gravity along the conical-shaped vessel as underflow. During this process, a flow of clean fluid, water, or hydrocarbons is induced to exit the vessel through the top, at the center of the swirling flow.

Figure 3: Cyclonic sand separator representation [3]

The underflow with the solids filtered is stored in an accumulation section below, that may be integral or separated from the cyclone.

Figure 4: Desander design variants

A known issue with cyclonic separators is the accumulation or solidification of sand that can plug the system. This can happen if the rate at which the sand is created exceeds the rate at which the sand is removed through pipes and valves. Dump valves with a predefined open cycle are ineffective since the sand formation can be non-constant and often varies. If the valve opens when no sand is formed, the multi-phase effluent fluid can directly go through the underflow, losing the product. If is opens too late, sand will fill the vessel, compromising overall operations.

Leaving the accumulator discharge valve open a little has continuous liquid loss and erosion on the discharge valve. For low pressure operation (<100 psig at the inlet) this method of operation is often used. However, for high pressure operation (>100 psig), or multiphase flow with oil in the fluid stream, or very abrasive solids, or problems with handling large volumes of discharged liquids – cracking open the discharge valve is not a reasonable solution (4).

An improved solution is to use flux lines or flow lines in the vessel. Using pressure sensors, the pressure difference created by the accumulation of sand can be detected and the flux line creates a downward flow avoiding sand plugging. These are however also ineffective if the sand creation rate is too high.

Operators can monitor sand production in separators and any other equipment, using a variety of techniques, such as analyzing fluid samples, numerical simulations and other indirect measurement techniques besides direct sand level measuring sensors like Rheonics Sand Detection Probe SRV-SDP. The objective in all these cases is to identify and address sand production problems early on and in some cases to automate the removal of sand.

Figure 5: Flux line in desanders

Need for real-time monitoring of sand level

Using equipment to monitor the sand level or concentration allows the user to:

Identify sand accumulations without human intervention
Schedule maintenance and cleaning of equipment
Take action early on (before sand deposits cause serious damage)
Plan process improvements
Analyze tendencies of the rate of erosion
Stabilize basements for full automation control
Reduce the need for visual checks and human supervision
Improve safety of operation and safety of personnel onsite

Different strategies for sand monitoring

Some technologies used for sand monitoring are listed in the next table.

Table 1: Sensor technologies for sand monitoring

Technology	Description	Pros	Cons
Acoustic sensors	Non-intrusive Measures the sound waves generated by sand due to particles hitting the surface of a wellbore, pipeline, or any equipment	Easy to install in multiple points of production. Useful to identify concentration locations and, up to some level, the size of particles.	Affected by fluid flow, bubbles, external vibration, etc. Hard to calibrate - lack of reliable calibration equipment. Does not work at high pressures or when there are deposits on the transducer.
Erosion probes	Intrusive and invasive probe. Measures the electrical resistance differences due to the loss of material from the probe’s metal surface caused by sand impact.	Provides direct and quantitative information on the amount and distribution of sand production. Used as a sample of potential damage to the equipment.	Affected by corrosion, fouling, or plugging. Performance and durability are compromised. Needs close monitoring for replacement. Measurement sensitivity is compromised due to process artefacts.
Sand concentration sensor	Measures the electrical resistance or capacitance of the fluid, expected to relate to sand concentration and mass flow rate in the fluid.	Offers continuous and real-time data Alerts any changes or anomalies.	Influenced by other properties of fluid, such as temperature, pressure, and salinity. Measurement sensitivity and confidence is severely affected by process artefacts like deposits.
Ultrasonic probes	Not intrusive or invasive The sensor works by sending out sound waves and determines the time in which they return. Works like a radar to determine if solids are formed in a certain section of equipment.	Provides real-time information without being intrusive. Handles vibration, infrared radiation, ambient noise, and EMI (Electromagnetic interference )radiation.	Readings can be affected by the external properties of fluids. Requires in-field calibration for each installation unless a specific flow cell or housing is used. Severly affected by wall deposits and need re-calibration to work with changing vessel wall conditions.
Vibration probes	Intrusive and invasive Operates at a certain frequency and detects the changes or deviations of frequency when it is in contact with fluid and solids.	Detects build-ups over time Can be set as a level alarm Can detect corrosion	Can be plugged by deposits.

Rheonics SDP - Sand Detection Probe

Rheonics SDP is an inline sand detection probe based on Rheonics viscometer SRV. The SDP sensor is used along with Ostrich software (Rheonics Sand Level Detection Software) for live infield detection of sand in separator equipment, including cyclone separators.

Rheonics SDP can be used to monitor the sand level in oil and gas industry equipment such as separators. This helps to protect production elements on the surface (oil and gas) and subsea side (subsea equipment).

The sensor operation is based on a torsional resonator that detects the changes in viscosity and density of a single- or multi-phase fluid. The sensor perceives the damping induced by the fluid in which it is immersed and its impact on resonant frequency.

The SDP is configured to sustain the working conditions of the system, for high pressures of up to 10K psi, with versions available for 15K psi and 25K psi. The sensor probe could also be mounted with different process connections like API flanges, Grayloc, Hammer Union, etc. This helps in the integration of the SDP sensor into different desanders and upstream or midstream pipelines and reservoirs.

Table 2: Specifications Rheonics Sand Detection Probe – SDP

Rheonics Sand Detection Probe - SDP
Extension Length	Customizable
Process Connection	Customizable
Max. Pressure Rating Variants	10,000 psi (690 bar, 69 MPa) 15,000 psi (1035 bar, 103 MPa) 25,000 psi (1724 bar, 172 MPa)
Material	Stainless Steel 316 Hastelloy C22 available for high corrosion environment
Certifications	Ex (ATEX, IECEx, JPEx, etc. )
Drawing	Rheonics SDP Drawing

Figure 6: Rheonics SDP – Sand Detection Probe

Visit the next article to learn about an installation case of the SRD Density and Viscosity Meter in oil and gas pipelines along the API standards.

Sand Level Detection Probe SDP Installation

As shown in Figures 2, 4, and 5, the SDP sensor can be installed in different points, or desander types, of the oil and gas upstream section.

The SDP sensor can be used to detect the presence of sand or particles that could “cement” and plug the underflow outlet on desanders. The sensor is placed at a predefined height in the desander that would indicate if the level and volume of sand are high enough to alert that action is needed from the controller (e.g. PLC) and actuator (e.g. valve) to remove the sand. Two probes can be used to signal low and high levels for better automation of sand removal valve control and avoiding any fluid from exiting the vessel in the solids outlet line.

The SDP readings of sand level provide information on the level of solid deposits in a multi-phased fluid. For example, if the fluid is mainly composed of water, the sensor outputs a reading of approximately 1-2cP. But when additional particles or fluids are presented (i.e. sand, oil, etc.), the readings change significantly.

Applications:

Automate accumulator solids removal in Desanders and separators used for

Oil and gas drilling
Produced sand removal
Well testing operations
Coiled tubing cleanup
Underbalanced drilling operations
Waste water treatment
Industrial process water treatment
Stormwater runoff treatment
Desalination plant
Recycling facility

Benefits:

Compact, robust design
No moving part, zero maintenance or servicing
Reduces cost of operating desander, making high-sand producing well production economical
Reduces solids erosion of accumulator discharge valve through event based activation
Helps reduce oil contamination of sand preventing sludge formation and alleviates difficult solids accumulation problems

Operations:

Available in a wide range of size and pressure rating
Available with ASME and API 6-A compliant flanges and other process connections
No onsite commissioning or calibration needed
Comes with Sand Level monitoring software with easy to set alerts and alarm levels
Possible to also activate the accumulator discharge valve directly from the sensor system
No operating pressure loss due to installation of sensor in desander or accumulator

Installation & Support:

Easy to install
Sensor probe built to fit any port on the desander
EX certified
No need for commissioning or calibration
Test mode to check operation and sensitivity of the sensor
Global support with remote diagnosis and configuration of the sensors

Automated Sand Removal System

The Rheonics sand level detection probe, SDP, leads the way for automated removal of sand accumulations in desanders and separators used in the Oil and Gas Industry. This is done by detecting the presence in line of sand or solids before they cause serious damages to the equipment, and sending a signal to activate a valve in the underflow line for sand transport and later removal.

Figure 7: Sand Removal Control with Rheonics SRV-SDP Sand Detection Probe

Numerous companies manufacture and operate Desanders catering to various industrial applications. Some of them are:

More on the Oil and Gas Industry

The oil and gas industry comprises the exploration, extraction, refining, transportation, and marketing of petroleum products. It is a multi-phased and complex process that heavily impacts the world’s economy, as it provides today’s most used energy source.

The steps comprised in the oil and gas industry are divided into the following areas or segments:

Upstream: The upstream segment is responsible for the exploration, discovery, and extraction of crude oil and natural gas from underground reservoirs.
Midstream: The midstream segment deals with transporting and storing crude oil and natural gas.
Downstream: The downstream segment focuses on refining the crude oil into its various products and marketing these products to consumers.

Nowadays, the oil and gas industry faces many challenges. From all of them, the environmental aspect is of utmost importance more so as alternative cleaner energy sources such as solar or wind power have emerged. The cost involved in this industry plays a key role nowadays and will have an increasing relevance in the future to determine the sustainability and profitability of this industry. The Oil and Gas companies are investing in cleaner strategies and are always on the lookout to improve efficiency as much as possible.

Wellbores used in the oil and gas industry [1]

More on Sand Production

Also known as sand ingress or sand invasion, this issue can be described as the access, accumulation, and solidification of sand or other particles inside the pipelines or machinery used in the oil and gas industry during extraction, transportation, and storage.

Wellheads are equipment used in the upstream area of the oil and gas industry to regulate the flow of hydrocarbons extracted from an underground well. These are the first pieces of equipment that risk deposits of sand, so they mostly work with Desanders or Sand Separators, detailed later in this paper.

The sand formation is a recurring issue, particularly in wells drilled in unconsolidated sandstone reservoirs. When the pressure in the reservoir drops below the formation’s strength, the sand grains can detach from the surrounding rocks and flow into the wellbore along with the produced oil or gas.

Some of the consequences of sand production are:

Reduced well productivity: Sand production can partially or completely block the wellbore, reducing the flow of oil or gas. This can lead to a decrease in production volume, quality, and revenue. Productions below forecast or economic levels can impact the profitability of a well detrimentally.
Damage downhole equipment: Sand deposit can erode and plug the tubings, valves, pumps, etc., causing costly damage and requiring premature replacement. This can affect the upstream and midstream segments if filtering or removal of sand is not correctly performed at extraction. Increased costs of operation can quickly make a well uneconomical to produce.
Wellbore instability: Sand production can destabilize the wellbore, increasing the risk of well collapse. This can be a serious safety hazard and may require the well to be shut in or abandoned. In addition, the financial impact would be significant and can compromise the overall reservoir access.

To solve the sand production problem, sand filtration and separation methods are usually applied in the production facilities.

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