Hydrocyclones have been used as a mode of sand separation within oil industry for many decades. The type generally used in oil and gas industry is the solid-liquid hydrocyclone and will be termed as “desander” throughout this manuscript.
Desanders have been used all over the industry for sand separation in applications related to separation of mud from drilling fluids during drilling, during the initial testing of exploratory wells wherein sand production is anticipated, for post frac production during the clean-up and also during production phase of the wells with sand ingress.
There are other methods used in the area of sand separation in surface facilities for the similar purpose like sand jetting inside vessels, using vessels itself as a means of separating solids via deposition and later cleaning them on regular basis and also conventional desander system. This paper would mainly deal in the latter conventional system.
When separating sand from a multi-phase or single phase stream, it is not only hydrocylone but is the installation of an entire system which can separate sand from the system, clean the separated sand and even includes the transfer of cleaned sand to safe area.
Hydrocyclone Desander For Solids Control Realated Topics
- Cyclonic Technology
- Design of Hydrocyclone for Drilling Solid Separation
- Desanders, Desilters And Hydrocyclones Arrangements
- Hydrocyclone Desander
- Hydrocyclone （Mud Cleaner, desander, desilter）Troubleshooting
- Why Desander Desilter (Mud Cleaners) Important In Solids Control
The basic designing of solid handling systems constituting of five key areas (Figure-2) i.e. separation of solids (via hydrocyclone or jetting or filters), collection of solids (via an accumulator), cleaning of solids from oil contamination (via washing systems), dewatering (disposal of liquid slurry being separated from cleaned sand) and haulage (transportation of sand to onshore or disposal as per local authority requirement.
Further, depending on the location, desanders in a production platform can be classified into various categories on the locations it is installed.
- Well head desanders – installation of hydrocyclone system with accumulator and flushing mechanism preferably at the upstream of choke designed for the particular well condition and flow rates;
- Bulk desander – to cater to many well streams and located preferably at the downstream of header;
- Other Locations – these are specific locations within the facility like separation of sand downstream of separator vessels, or installation of a single phase hydrocyclone at upstream of crude oil transfer pump or cleaning up the well post completion or post fracturing.
Later sections will discuss the key factors important for selection of bulk or well head or other desander. Company had been facing serious sand production issues in many of their fields since last few decades. To resolve the issues related to sand, a dedicated team was set-up and a structured approach (Holistic Sand management approach) was applied since 2014.
The approach constituted of development of a centralized multi-disciplinary team (as the company operates on an asset based model) named as ‘Central Sand Team’ (CST) along with asset based Regional Sand Teams. The approach till date has resulted in developing a culture within the Company to tackle sand in a focussed way. The approach includes consideration of all aspects of sand within the system right from sub-surface, surface handling and disposal.
Use Desander Execution Strategy
With holistic sand management approach being applied in various fields and platforms, the initial study recommended installation of desanders in a few platforms to handle sand at surface for integrity of the facility and production optimization. This led to the need of looking into retrospect on the performance of existing desanders and strategize the selection, procurement and installation of upcoming desanders.
The entire enhancement of process to combat the challenges of >10 years was planned to be conducted in following way:
- Initial data collection of existing desanders;
- Finding gaps in technical selection and entire procurement strategy, if any
- Conduct market survey to gauge technical capability / technology in the current market
- Strategize on technical selection of desander
- Strategize on procurement and contract management strategy
Existing Process & Gaps
During the study of past installations of desander systems within the Company, team had to dig up earlier records some of them were available and others not.
Initial Data Collection
The team collected data from the existing desanders along with the results and performance. The main highlights of the initial findings i.e. company experience on past decade on the desanders (all well head type) were as follows:
- Total number of desander installations: 33
- Operational i.e. separating sand: 11
- Installations on-going till the results were out: 7
- Non-operational: 15
On the non-operational part, there were 7 desanders which were out of specifications i.e. the flow rate for which they were designed and installed were non-existence and due to all the 7 being in a category (mentioned above), no retrofit can be done. They were termed under absolute. 5 out of 15 had maintenance issues due to erosion in liners, etc. or no spare parts and rest had the well issues and therefore were nonoperational.
Out of the 33, only 6 were under Category B and rest all were Category A. It is to be highlighted that even for the desanders which were termed as operational, it was characterized so, because the sand was being collected in the accumulator. Uncertainties still lied on the efficiency and the amount of sand being carry over downstream of desander.
It was concluded from the entire data collection and basic analysis that there was a gap in a standard process to select, procure, install and utilize desander systems. First objective like any other process improvement effort was to identify gaps.
Finding Gaps in technical selection and execution processes
The main findings of the previous studies and related gaps were as follows. For clarity on the challenges, they have been classified under technical & management challenges.
- Technical Gaps
- Technology limitation: Hydrocyclones concept is mainly on separation of liquid-liquid, liquid-solid, gas-solid, etc. i.e. only on the 2-phase separation, but with slurry mixture and hydrocarbon flow, the challenge was to separate solid from both liquid and gas stream. For some cases, the desander did not perform due to high gas flow variation resulting in efficiency.
- No defined process of selection: One of the biggest technical gap was less awareness on the selection of desanders and process of how to select the type of desander that best for specific environment. This particular reason resulted in other gaps as mentioned below.
- Deployment of mainly static desanders: It was observed that few wells flowed out of the operating envelope and with no flexibility of changing the basic design of separators, they resulted in non-functioning category.
- Pressure drop and size separation: Due to old and mature fields, the THP on the surface were in low ranges (<70 psi). With the efficiency of particle size separation and limited pressure, few desanders were not able to separate the sand efficiently.
- High reliance on service provider for technical design and specifications.
- Minimal performance monitoring: It was a general consensus obtained from Operators offshore, that they considered desander as successful functioning as long as they were able to observe sand being separated after flushing the accumulator. This was the reason that few of the existing desanders were assumed working and later after a little more investigation turned out to be not as efficient as expected.
- Managerial / Execution Challenges
- Ad-hoc solution: The records stated that installation of desanders were more on the reactive basis than a well-planned basis. With sand being produced in a particular well and avoiding that well to be kept idle, desanders were adopted as quick solution but with various gaps as had been already mentioned and will be detailed in points to follow. This was the biggest gap and root cause of many other gaps below in the entire process. This not only lead to high cost but events like single sourcing, get from the one easily available.
- No One discipline: Due to the fact that there was no focal point for the technology, it was mainly driven by surface operations and process engineers. There was minimal or at times no input from production surveillance or the production technology group who had better understanding on well parameters and future performance of the well, which lead to incomplete selection.
- No after sales services and only Purchase strategy: Desanders earlier were considered as one-time buy product. Due to less awareness on the designing and long term usage, the scope was only limited to purchase rather than a rental contract or even maintenance contract. This resulted in few non-working absolute products.
- Value leakage: As every purchase above was not an onus of a single discipline or team, there was a huge gap from purchase till performance monitoring and efficient reporting.
- Data Management: With no one onus and also dearth of any long term maintenance, the data base on the performance, design and other critical parameters on desanders were never constantly updated or recorded.
- Vendor capability & Service quality: With mainly ad-hoc requirement, there was very basic quality check on the service being provided by vendor and due to time limitations on delivery even capability of vendor to be technically capable in understanding such sand management solutions were not thoroughly done.
With series of gaps being observed and numerous lessons learnt as in this section, it was obvious that the entire strategy needed a revamp. As the installations were relatively not new and sand management efforts within industry had obviously rose to higher levels, it was necessary for the team to gauge the existing technology emerging within the industry.