I. BACKGROUND
For companies that business lies in upstream industries where continuously to explore new reservoirs to deliver the amount of gas according to a contract agreement. Exploring new potential reservoir, installing wellhead and tie-in the flow line to existing manifold called well connection. Well-connection is the heart that pumps the company (upstream industries) to operate and run. The various engineering work of well-connection is repetition and could be grouped based on typicality. Since well-connection is repetitive work and a tight schedule, often it is overlooked. Improvement is always open if we have comprehensive knowledge of technology.
Improvement along with cost reduction will have outcome optimization. For a mature exploration field, the term “optimization” plays a major role in cost savings. Optimization is targeted to reduce significant costs either Capex (Capital Expenditure) or Opex (Operating Expenses).
Cost reduction is responsible for all entities in the organization.
As a Senior Instrument and Control Design Engineer, you often encourage yourself to bring a new idea for improvement and delve into the details. On several occasions, improvement is proposed and requested by the production and process department. Other disciplines such as electrical, instrument and control systems will support this request. This particular improvement, it is initiated by self-insight. The objective was to gain self-accomplishment to give added value to the company.
II. OBJECTIVES
For this case improvement and cost optimization is addressed on wellhead and wellhead flow line measurement which is part of well-connection work.
III. EXISTING DESIGN
III.1. WELLHEAD
Below are the typical schematic connection to measure pressure and temperature on the wellhead x-mass tree. The Wellhead platform is located remote where no electrical power is available. The measurement uses a paper chart recorder. The paper chart recorder movement is either powered by internal batteries or mechanical key wounding.
Paper chart recorders (well-known brand Barton) are measuring and recording wellhead parameters as follows:
- Annulus Pressure (Casing Pressure)
- Tubing Pressure (Production Pressure)
- Tubing Temperature (Production Pressure)
III.2 FLOWLINES
Whilst the typical measurement flow rate (compensated) on flow line as seen below. Measure parameters are as following:
- Differential Pressure (inH2O)
- Pressure upstream Flow Element(static, barg)
- Temperature flowline (degC)
Within this configuration, NUFLO Scanner 2000 is using internal battery 7.2V 17Ah. The internal battery is not rechargeable. The internal battery should be continuously expedited. The other problem is a decision when to purchase the internal batteries in order not too long place in storage. Guidelines for storing batteries should be followed to avoid excessive self-discharge.
IV. THE IMPROVEMENT and OPTIMIZATION
Based on the two device measurement on wellhead and flow line, it could be integrated only using NUFLO Scanner 2000 as schematic connection below
This improvement is to optimize the capability of NUFLO Scanner 2000. NUFLO Scanner 2000 able to receive additional 2 analogue input if it utilizes additional cards (expand I/O).
2 Analogue input will be assigned for:
- 1 ea analogue input to be assigned for Pressure Tubing (production)
- 1 ea analogue input to be assigned for Pressure Annulus (casing)
The remaining tubing temperature will utilize the RTD sensor currently being used for the temperature flow line. Meanwhile, RTD on the temperature flow line will be replaced with a temperature gauge.
You will instantly notice, the temperature is different between the wellhead and the flowline. The temperature on the flowline is lower than the temperature on the wellhead. If we use input temperature from the wellhead it will affect the flow rate calculation. But this difference is not significant and it is acceptable.
Since this application is not for metering purposes but rather to control manual choke valve opening. In addition, throughout the well life cycle, fluid density is held constant, thus temperature will not main factor for flow rate compensation.
The other option is to use temperature on wellhead only for recording, not as input for flow rate compensated equation. The temperature for flow rate compensated is considered as constant, set by the metering team.
Both pressure sensor for pressure casing and tubing signal is conveyed with an output of 4-20mA. As stated previously, an existing configuration is using internal power. In order NUFLO Scanner 2000 could be as loop power two wires, it will require an external power supply 24VDC.
The external power supply 24VDC is provided by the lithium-ion battery power pack. It is rechargeable meanwhile internal battery is not rechargeable.
The lithium-ion battery power pack should be equipped with a protection feature such as a protection circuit that limits the peak voltage of each cell during charge and prevents the cell voltage from dropping too low on discharge. In addition, the cell temperature is monitored to prevent temperature extremes. The maximum charge and discharge current on most packs are is limited to between 1C and 2C. With these precautions in place, the possibility of metallic lithium plating occurring due to overcharge is virtually eliminated.
V. ADVANTAGE & DISADVANTAGE
Despite improvements with its advantages, any modification has its drawback to be considered. Often disadvantage comes from other aspects which not related to improvement.
The following are advantage of this improvement
- Paperless
- Higher accuracy reading due to digitizing reading
- All data parameters are recorded for up to 30 days
Meanwhile the disadvantage as following
- High initial cost for battery power pack (including charger)
- Additional work for carrying battery power pack for recharge
- To define who will be responsible to maintain the lithium-ion battery pack, electrical team or the instrumentation team.
- Not yet found a product that conforms to hazardous area certification for this battery type. Hence, it should be located outside zone 2 (non-classified area
VI. POWER CONSUMPTION
The remote wellhead platform does not have an electrical source. External power will be provided by power pack batteries. Batteries power packs are very custom, in order to able to select the battery power pack. Power consumption should be calculated.
Based on the average lifetime of an internal battery, the average current consumption NUFLO Scanner 2000.
1 ea lithium-ion battery pack with 24VDC and 46.99 Ah may have different weights among the manufacturer. Battery lithium-ion with a capacity of 40 – 50Ah 24VDC would weigh around 11 – 13 kg. It is considered heavy. In this design, I decided to select batteries with weights 5 up to 7 kg. However, within this selection weight, the capacity will be rated 20 – 25 Ah. The selection of battery weight is related to the charging method. The expected duration of the lifetime will reduce up to 45 days.
VII. CHARGING METHOD
A lithium-ion battery is critical during charging. This is why I decide no automatic charging onsite. Moreover, power by solar panels is not considered since this material is highly attractive for thievery. If the batteries have reached minimum level voltage, then the batteries will be carried out to onshore (accommodation) for recharging. Since the charging is onshore, attention should be address to consider the weight of batteries to be hand carry.
1 ea lithium-ion battery pack will cover 1 NUFLO Scanner 2000 with associated sensors. Yes, you could increase capacity Ah by configuring parallel but since this installation is in a hazardous area it would be safer not to configure batteries in parallel or series. Parallel/series battery configuration has the possibility to generate a spark when fixing or dismantling the connection bar. So I recommend only using an individual battery pack. As possible the location battery should be categorized as a non-classified area (outside zone 2).
Onsite, batteries will continue to discharge. Therefore, the lithium-ion battery pack should be facilitated with a battery management system in order to maintain the voltage does not go below the minimum voltage. When the battery has reached the minimum it should able to give an indication to the operator and it will automatically cut power to the device (load) in this case NUFLO Scanner 2000 and accessories sensors.
VIII. BILL OF MATERIAL
Next are selection material to perform the modification
IX.CAPITAL COST
I could not provide comprehensive capital cost. This capital cost intended for comparison. I didn’t consider the cost of man-hour to perform this modification.
The gain of improvement is estimated USD 1788.45 (USD 5500 – USD 3711.55). Usually, this value is small compared to overall well-connection work. However, if in 1 year at least there are 50 well connections, this saving is worthy.
Conventional Barton Chart approximately $ 5500 USD
X. IMPLEMENTATION
I have not yet implemented this improvement and optimization due to the procurement company policies of batteries. Company has restricted import product directly without any local agent. We are trying to solve this issue. Hopefully in the future, I could update the result.
XI. REFERENCES
Instrumentation and Control System 