Report on Shahbazpur Gas Field

SHAHBAZPUR GAS FIELD

1.  Description of Field

Introduction

Shahbazpur Gas Field was discovered by BAPEX (Bangladesh Petroleum Exploration and Production Company Ltd) in 1995 at Bhola, Bangladesh. The production was commenced in 11^th May, 2009. In the earlier stage of production, the plant was based on LTX units till late 2014. In 2015, the plant was changed to TEG Dehydration unit base from LTX unit base due to the high condensate and water production rate. Till now, it has the highest production rate compared to the other gas fields owned by BAPEX.

Objective

• To supply gas to local residents in Bhola
• To get attached with the national energy grid of Bangladesh
• To supply gas to the 220 MW power plant which is under planning (Project Name: Bangladesh Bhola IPP)

Salient Features

1.	Location	:	Borhanuddin, Bhola
2.	Number of Wells	:	04
3.	No of Producing Wells	:	03
6.	Daily Production	:	50 MMSCF (10th January, 2019)
7.	Type of Process Plant	:	Glycol Dehydration
8.	Capacity	:	70 MMscf/D (2 Glycol Dehydration Tower, Capacity of 35 MMscf/D each)
9.	Cumulative Production	:	39.03 BCF (Dec’17)
10.	Total Reserve	:	1.6 TCF

1: Geology

The Shahbazpur gas field is located in Foredeep area of Bengal basin or can be said more precisely in the Hatia trough. The Foredeep part of the Bengal basin is located towards west from eastern fold belt where intensity of folds decreases continuously and Foredeep unit is characterized by only mild or no folding. So, the sedimentary layers are generally horizontal to sub horizontal and are free from major tectonic deformation in the Foredeep area. This unit covers the central part of the basin and is represented by river to delta plain topography at the surface.

Table 1.2.1: Stratigraphy and Lithology in Shahbazpur Structure 

Depth	Age	Group	Sequence	Lithology
0-480	Recent		Alluvium (480)	Loose unconsolidated sand with occasional clay
480-1505	Pleistocene	Dupi Tila	SB-I (1025)	Shale with occasional occurrence of interbedded sandstone and siltstone
1505-2010	Pleistocene- Pliocene	Tipam	SB-II (505)	Shale and Sandstone
2010-2750	Plio- Miocene	Surma	SB-III (740)	Sandstone and shale
2750-3631	Miocene		SB-IV (881)

2. : Reservoir and Well Condition

Reservoir Condition

The Shahbazpur structure is a subsurface anticlinal structure situated in the middle of the Bhola Island in the northern margin of Hatia trough of Bengal Foredeep. The Hatia trough is bounded by the Chandpur-Barisal high in the northwest, and by the Chittagong-Tripura Fold Belt in the southeast. The alignment of the NW-SE trending oval shaped Shahbazpur structure is parallel to the Kutubdia structure which is located in Bay of Bengal to the south. Shahbazpur Structure is surrounded by Muladi Structure to the Northwest and Kutubdia Structure to the Southeast. The structure started growing probably during Late Miocene and its acme of development took place during Mio-Pliocene sedimentation and ended in Pleisto-Pliocene time (Mondal et al.9). This structure is relatively 69.4 m higher than the Kutubdia structure. The amplitude of the structure increases with depth. There is no surface expression of the Shahbazpur structure

Reservoir Depth: 3480 m 

Reservoir Pressure: 5400 Psi 

Reservoir Temperature: 195 F

Well Condition

 Tubing Diameter: 4 in 

Casing Diameter: 7 in

Table 1.3.1: Well Conditions of Shahbazpur Gas Field

Well Name	Type of Well	Condition	Wellhead Pr (psi)
Well-1	Vertical	Under Workover	4000
Well-2	Directional	Under Production	3600
Well-3			3800
Well-4			4200

Figure 1.3.1: Well-03 of Shahbazpur Gas Field

3. : Fluid Properties

Sales Gas:

The sample was tested at 94 F and 540 psi by BAPEX Lab.

Table 1.4.1: Molecular Composition

Components	Mol%	Wt%
Nitrogen	0.473	0.766
Carbon Dioxide	0.809	2.056
Methane (C1)	93.384	86.515
Ethane (C2)	4.152	7.212
Propane (C3)	0.785	2.000
iso-Butane (i-C4)	0.233	0.782
n-Butane (n-C4)	0.083	0.280
iso-Pentane (i-C5)	0.026	0.110
n-Pentane (n-C5)	0.013	0.052
Hexanes (C6)	0.012	0.061
Heptanes+ (C7+)	0.029	0.166
Presence of Hydrogen Sulfide	Absent

4. : Process Flow Diagram

The process flow diagram and site view of the process plant, Shahbazpur Gas Field are given below:

Figure 4.5.1: Process Flow Diagram of Shahbazpur Gas Field

Figure 1.5.2: Site View of Process Plant of Shahbazpur Gas Field

5. : Control System

In this field, the operations are controlled by Distributed Control System (DCS). Still, there are some operations controlled manually to reduce the complexity of the plant.

Distributed Control System (DCS)

A distributed control system (DCS) is a computerized control system for a process or plant usually with a large number of control loops, in which autonomous controllers are distributed throughout the system, but there is central operator supervisory control.

Basic Elements of DCS: There are three basic elements of DCS. These are:

1. Engineering PC controller
2. Communication Media (Transmission Cables)
3. Distributed Controller and Logic Unit

Principle of Working: These distributed controllers are connected to both field devices and operating PCs through high speed communication networks as shown in Figure 4.6.1. Discrete Field devices such as sensors and actuators are directly connected to input and output controller modules through communication bus. These field devices or smart instruments are capable of communicating with PLC’s or other controllers while interacting with real world parameters like temperature, pressure, etc. Controllers are distributed geographically in various section of control area and are connected to operating and engineering stations which are used for data monitoring, data logging, alarming and controlling purpose via another high speed communication bus.

Figure 1.6.1: Architecture of DCS Panel

6. : Process Units

There are two process plants (Plant-A, Plant-B) and each plant has same process units. These are:

1. Three Phase Separator
2. Header
3. Water Bath Heater
4. Two Phase Separator
5. TEG Dehydration Tower
6. Sales Gas Scrubber
7. Condensate Flash Separator
8. CPI Unit (Corrugated Plate Interceptor)

Three Phase Separator:

A vessel that separates the well fluids into gas and two types of liquids: oil and water is called a Three Phase Separator. A three phase separator can be horizontal, vertical or spherical. This type of separator is commonly called a free-water knockout because its main use is to remove any free water that can cause problems such as corrosion and formation of hydrates or tight emulsions, which are difficult to break.

 

Figure 1.7.1: Three Phase Separator

 Header:

In a gathering system, Header is a pipe arrangement that connects flow lines from several wellheads into a single gathering line. A header has production and testing valves to control the flow of each well, thus directing the produced fluids to production or testing vessels. Individual gas/oil ratios and well production rates of oil, gas and water can be assigned by opening and closing selected valves in a header and using individual metering equipment or separators.

Figure 1.7.2: Production Header

Water Bath Heater:

The primary applications for Water Bath Heaters include:

• Heating Natural Gas prior to pressure reduction manifold to prevent freezing or expansion
• Hydrate Prevention
• Increasing separation efficiency by heating processed upstream fluid

The heater consists of three main components:

1. Shell
2. Fire Tube
3. Process coil

Two Phase Separator:

A vessel that separates the well fluids into gas and total liquid is called a Two Phase Separator. A two phase separator can be horizontal, vertical or spherical. The liquid (oil, emulsion) leaves the vessel at the bottom through a level-control or dump valve. The gas leaves the vessel at the top, passing through a mist extractor to remove the small liquid droplets in the gas.

Figure 1.7.4: Two Phase Separator

 TEG Dehydration Tower:

The purpose of a glycol dehydration unit is to remove water from natural gas and natural gas liquids. When produced from a reservoir, natural gas usually contains a large amount of water

and is typically completely saturated or at the water dew point. This water can cause several problems for downstream processes and equipment. At low temperatures the water can either freeze in piping or, as is more commonly the case, form hydrates with CO2 and hydrocarbons (mainly methane hydrates).

Figure 1.7.5: Glycol Dehydration Tower

 Sales Gas Scrubber:

The purpose of a gas scrubber is to eliminate harmful particulates and liquid hydrocarbons from natural gas. A natural gas scrubber system works by using particle filters, coalescers, mesh pads, and other devices to remove pollutants from the gas stream. This type of gas scrubbing is the preferred way to ensure that natural gas is clean and dry for industrial use.

Condensate Flash Separator:

Flash Separator separates condensate from water and sends the condensate part to the storage tank. The water portion then goes to the CPI unit.

CPI Unit:

Process Group CPI Units are designed to remove free oil and suspended solids from water as a primary stage of water treatment and utilize plate packs as the main separation device. The plate packs are designed with specific spacing and alignment to allow solids to settle and fall to the bottom while simultaneously allowing oil drops to rise and coalesce, thereby reducing the oil and solids loading from the downstream water treatment train and smoothing out flow slugging.

Figure 1.7.6: CPI Unit

7. : Equipments

Globe Valve:

A globe valve, different from ball valve, is a type of valve used for regulating flow in a pipeline, consisting of a movable disk-type element and a stationary ring seat in a generally spherical body.

Butterfly Valve:

A butterfly valve is a valve that isolates or regulates the flow of a fluid. The closing mechanism is a disk that rotates.

Non-Return Valve:

A non-return valve allows a medium to flow in only one direction. A non-return valve is fitted to ensure that a medium flows through a pipe in the right direction, where pressure conditions may otherwise cause reversed flow.

Pressure Control Valve (PCV):

A PCV valve that's supposed to regulate the flow of these gases is the heart of most PCV systems (some newer vehicles don't have a PCV valve). The PCV valve routes air and fuel from the crankcase back through the intake manifold to the cylinders rather than allowing them to escape into the atmosphere.

Temperature Control Valve (TCV):

A temperature control valve is just like any other control valve. The only difference is that  the control valve helps to maintain the temperature of a desired process at a specific level.

Level Control Valve (LCV):

A level control valve or altitude control valve is a type of valve that automatically responds to changes in the height of a liquid in some storage system.

Plug Valve:

Plug valves are valves with cylindrical or conically tapered plugs which can be rotated inside the valve body to control flow through the valve. The plugs in plug valves have one or more hollow passageways going sideways through the plug,

Measuring Tape:

It is used for measuring the water and condensate level in the condensate storage tank. Water finding paste is placed on the measuring tape and then the measuring tape is inserted into the tank. When it finds water it changes its color and thus it indicates the water level where the color is changed. Once the water level is read, the condensate level is calculated from the previous record of condensate level comparing with the water level and the total height of the storage tank.

Figure 1.8.5: Reading Water and Condensate Level by Measuring Tape

Kimray Pump:

It is such a pump that uses energy exchange theory and doesn’t need any external energy to start. So it has a great use in industrial purpose where external power is quite difficult to manage. It generally starts by differential pressure. It is mainly used for Glycol Regeneration process.

Figure 1.8.6: Kimray Pump

I2P Converter:

A “current to pressure” converter (I/P) converts an analog signal (4 to 20 mA) to a proportional linear pneumatic output (3 to 15 psig). Its purpose is to translate the analog output from a control system into a precise, repeatable pressure value to control pneumatic actuators/operators, pneumatic valves, dampers, vanes, etc.

Figure 1.8.7: I2P Converter

Barton Chart Planimeter:

Barton  chart  recorders  are  the  industry  standard  for  accurate,  reliable  measurement   and recording of pressure, differential pressure, and temperature in a wide variety of applications.  In  addition,  DP  models  utilize  Barton’s   rupture-proof   bellows  DPU  as the actuating unit with features like overrange protection and pulsation dampening.

Components: 1) Case 2) Chart Drive 3) NuFlo^TM Chart 4) Recording Mechanism 5) Pressure Element and 6) Thermal System

Figure 1.8.8: Barton Chart Planimeter

8. : Pipe Schedule, Fittings and Valve Ratings

Pipe Schedule:

There are 5 pipe schedules used in the process plant. These are: XXS, 160, 120, 80 and 40.

Valve Rating:

There are 4 differently rated valves used in the process plant. These are: #2500, #1500, #600

and #150.

Table 1.9.1: Maximum Allowable Non-Shock Pressure (Psi)

Pr Class (lb)   Temp (F)	#150	#600	#1500	#2500
-20 to 100	285	1480	3705	6170
200	260	1350	3375	5625
300	230	1315	3280	5470
400	200	1270	3170	5280

9. : Flow Calculation

Flow Calculation by Digital Meter:

 

Rate of Flow, Qh = C`√(hwPf) in MMSCF/d

Where, C` = Fb * Fpb *Ftb * Fg * Ftf * Fr * Y * Fpr * Fm and Fb = Basic Orifice Flow Factor

Fpb = Pressure Base Factor

Ftb = Temperature Base Factor Fg = Specific Gravity Factor

Ftf = Flowing Temperature Factor Fr = Reynold’s Number Factor

Y = Expansion Factor

Fpr = Supercompressibility Factor Fm = Manomatric Factor

Input Variables: 1. Pipe Inner Dia (ID) in inch

2.               Orifice Inner Dia (ID) in inch

3.               Specific Gravity of Gas

4.               Flowing Temperature (in F)

5.               Gauge Pressure (in PSI)

6.                Avg Differential Pressure (in H2O inch column)

Optimum Flow Calculation by ECLIPSE:

For well no-2, the officials of SBZ gas field have manually found that considering all factors and variables the optimum flow rate is around 14 MMscf/d. But here, we have done an experimental simulation of optimum flow rate using ECIPLSE software and it came out 14.6 MMscf/d which is close to the field result.

Input Variables:

Tube Dia = 4.5 in Casing Dia = 7 in

WGR = 1.1229 bbl/ Mscf CGR = 0.12 bbl/ Mscf

PI = 11.42 Mscf/ d. psi SG of Water = 1.00

SG of Condensate = 0.9 SG of Gas = 0.5992

Max Flow Rate = 20 MMscf/d Min Flow Rate = 5 MMscf/d Reservoir Pr = 5400 psi

Table 1.10.1: Temperature Data

Measured Depth (ft)	TVD (ft)	Temperature (F)
0	0	155
11480	11480	195

Result:

Optimum Flow Rate is 14.6 MMscf/d at THP = 350 psi

Figure 1.10.1: BHP vs Flow Rate Curve with IPR of Well No-02

10. : Consumer

There are four major consumers of the sales gas produced by Shahbazpur Gas Field. These are:

Table 1.11.1: Consumers of Sales Gas

Consumers	Capacity of Power Plant (MW)	Daily Demand (MMscf)
Aggreko	95	20-26
PDB	225	33
PP Venture	34	8
Household	N/A	0.7-1

11. : Health and Safety Management

Fire Fighting System:

For fighting system, the plant was installed following equipments:

1.         Smoke Detector

2.         Fire Alarm

3.         Jockey Pump

4.         2x Diesel Pump

5.         Fire Extinguishers (CO2, Dry powder, Fire bucket etc.)

There is a fire pond for spraying water to deal with fire. It has almost 6000 m³ of water.

Conclusion

Agmor Consortium and Pegasus International were awarded PMC and Design Engineering of the surface facilities of the Shahbazpur Gas Field by BAPEX. The scope of responsibilities included detailed field survey and soils assessment of the plant site, preparation of preliminary design and specification of the Glycol Dehydration Process Plant, Condensate Tank, Flowline, Burn Pit and Generators. Project activities covered Hazards Evaluation and Environmental Impact Assessment Mitigating Measures and Safety Procedures. Other activities comprised of:

• Preparation of EPC Enquiry Documentation
• Bid Evaluation
• Contract Negotiations & Award
• Oversee Contractor’s Detail Design
• Field Supervision
• Progress Monitoring and Control
• Contractor Invoice Approval