Acid Gas Injection (eBook)

Field, Data, Simulation

John J. Carroll, Ying Wu, Mingqiang Hao, Weiyao Zhu (Herausgeber)

eBook Download: EPUB

2025
684 Seiten
Wiley-Scrivener (Verlag)
978-1-394-35627-0 (ISBN)

Infos

This ninth and final volume in the series, Advances in Natural Gas Engineering, covers gas injection into geological formations, one of the hottest topics in the industry, with contributions from some of the most well-known and respected engineers in the world.

This timely book focuses on gas injection into geological formations and other related topics, which are very important areas of natural gas engineering and build on previous volumes. It includes information for both upstream and downstream operations, including chapters detailing the most cutting-edge techniques in acid gas injection, such as acid gas disposal, modeling, and much more.

Written by some of the most well-known and respected chemical and process engineers working with natural gas today, the chapters in this important volume represent the most state-of-the-art processes and operations used in the field. Not available anywhere else, this volume is a must-have for any chemical engineer, chemist, or process engineer in the industry. Advances in Natural Gas Engineering is a series of books meant to form the basis for the working library of any engineer working with natural gas today.

John J. Carroll, PhD, PEng, is the Director, Geostorage Process Engineering for Gas Liquids Engineering, Ltd. in Calgary, Canada. Dr. Carroll holds bachelor and doctoral degrees in chemical engineering from the University of Alberta, Edmonton, Canada, and is a registered professional engineer in the provinces of Alberta and New Brunswick in Canada. His fist book, Natural Gas Hydrates: A Guide for Engineers, is now in its second edition, and he is the author or co-author of 50 technical publications and about 40 technical presentations.

Ying (Alice) Wu is currently the President of Sphere Technology Connection Ltd. (STC) in Calgary, Canada. From 1983 to 1999 she was an Assistant Professor and Researcher at Southwest Petroleum Institute (now Southwest Petroleum University, SWPU) in Sichuan, China. She received her MSc in Petroleum Engineering from the SWPU and her BSc in Petroleum Engineering from Daqing Petroleum University in Heilongjiang, China.

Mingqiang Hao, PhD, is a senior engineer of reservoir engineering and the deputy chief engineer of Oilfield Development at the Research Institute of Petroleum Exploration &Development (RIPED), PetroChina. His current main research interests focus on CO₂-EOR and horizontal well for low permeability reservoirs.

Weiyao Zhu is a Professor of Mechanics at the University of Science &Technology, Beijing, holding the Chair in the Department of Building Environment of Energy Engineering and the Institute of Applied Mechanics. He is also the director of Mechanical disciplines at the University of Science &Technology Beijing. He has served as an editor of some Chinese academic journals, and as an Associate Editor of the Journal of Natural Gas Engineering. He has published twelve books and over 330 research papers and has 17 patents and 26 software copyrights to his credit. He has also been recognized with many professional and academic awards.

Textauszug

1
Acid Gas Injection from Startup to Stability—A Recap of 3 Years of Operation and Troubleshooting

Loni van der Lee1, Jordan Watson1, Laura Creanga2 and James van der Lee3

1Tidewater Midstream, Grande Prairie, AB, Canada

2SLB, Calgary, AB, Canada

3DexPro, Calgary, AB, Canada

Abstract

The following work summarizes operational challenges encountered at the Tidewater Pipestone facility during startup and first years of operation, specific to AGI. Challenges commonly associated with facility startups were experienced at PSGP (Pipestone Sour Gas Plant) and this was also true for acid gas treatment and handling units. Some of the challenges we encountered in the first few years of operation include maintaining amine unit stability, compressor control/loading, temperature control, well tubing failure, diaphragm failures in acid gas pumps, management of acid gas compression/injection during maintenance and unplanned outages, and development of site-specific maintenance and operational best practices. A combination of operational experience, modeling, fluid analysis, equipment failure analysis, and engineering expertise from multi-disciplinary teams was utilized to mitigate and resolve operational challenges including adaptations to the operational procedures utilized at PSGP to minimize process upsets and equipment downtime based on operational history and experience, engagement with third party vendors and strategies developed for improved unit performance, and use of process simulation as a tool to predict the potential impact of deviant operating conditions and their possible contribution to areas of challenge.

1.1 Introduction

The Tidewater Midstream Pipestone Sour Gas Plant (PSGP) is located approximately 20 km west of Wembley, Alberta. Startup commenced in September 2019 of the facility that was designed to process 100 MMSCFD of sour gas from Montney shale production and its associated liquids.

The amine unit was designed to utilize DGA® (Huntsman) for sweetening gas at 5% H2S and 0.3% CO2, with a resulting target composition of the processed dry acid gas of 95% H2S and 5% CO2. As such, acid gas dehydration occurs via two five-stage compression and cooling trains. After the last stage of compression, diaphragm pumps are utilized to raise the fluid to injection pressures of approximately 20 MPa. Dense phase fluid is then injected into two acid gas wells, both in the Stoddart formation (carbonate aquifer) at ∼3,000-m depth, with a reservoir pressure of 28 MPa, with an approximate permeability of 10 mD. Power is generated onsite by two gas turbines.

Table 1.1 Design and current conditions.

	Design	Current

Acid gas flow rate

160 E3m3/day 5.66 MMSCFD

Composition

H2S

90 mol%

80–85 mol%

CO2

5 mol%

9–13 mol%

H2O

5 mol%

6 mol%

Water content after 4th stage

3.4 g/Sm3 214 lb/MMSCF

4.3–4.8 g/Sm3 275–305 lb/MMSCF

1st stage suction temperature

43.3°C

40–45°C

1st stage suction pressure

34.5 kPa [g]

42–45 kPa [g]

5th stage discharge pressure

6,895 kPa [g]

5,250–5,600 kPa [g]

Injection temperature

60°C

40°C

Injection pressure

23 MPa [g] (max pump SD)

15–20 MPa [g]

The original design and current operating range for the acid gas compression/injection train are as shown in Table 1.1.

Figure 1.1 Schematic of acid gas injection train.

Figure 1.2 Design vs. current compression stages.

The acid gas injection train is comprised of three sections/skids—acid gas compression (2X50%), acid gas pump (2X50%), and acid gas injection. Figure 1.1 shows the major pieces of equipment and points of control.

Given the high H2S concentration expected in the acid gas processed at PSGP dehydration was expected to be reasonably achieved via compression and cooling even if CO2 concentration should increase, as can occur in area production. In 2019 acid gas H2S content was ∼90 mol% (dry basis) but since late 2022 this has dropped to 85 mol% (dry basis) as CO2 concentration has increased. Figure 1.2 shows the design and a potential current operating curve, along with two operational phase envelopes and the hydrate curve at compressor suction. The difference in 5th stage discharge pressure is a function of both composition and temperature exiting the cooler upstream of the accumulator on the pump skid.

1.2 Startup: Ideal vs. Actual

The startup of a new facility, let alone a sour gas plant, is always going to be an enlightening experience. Operation is not steady, not typical and not tuned. Every design “assumption” is simultaneously tested under circumstances where even the best design can be challenged at times. It is also an opportunity for the more mundane best practices around valving and isolation to standout as commissioning, startup activities and frequent process trips will direct flow at conditions that are far from ideal and modifications to better align actual and ideal will be frequent and require immediate attention and alteration. An isolation philosophy that considers timely repairs and maintenance will be invaluable. This includes isolation on flare, drain, and utility connections as these are sometimes less considered but can add substantial downtime to repairs and maintenance if no isolation is available to allow for safe work. Also, it is vital that compressor drains on acid gas package be protected with check valves so there is no potential back flow into the compressor/pump skid. The cost of clean-up alone is far greater than that of a few check valves let alone the associated downtime.

During the initial facility startup interactions between the startup sequence and permissives of the separate compressor-pump-injection skids caused some challenges. When operating an acid gas injection system similar to that at PSGP, where each of the three segments are designed as individual packages, it would be helpful for design teams to carefully review the startup and shutdown sequences with the operations team, with vendor and programming support on hand. As one example, a minimum accumulator level will be required to start the acid gas pumps. Once that permissive is met the pumps need to start before the accumulator hits high-level shutdown. The default timer setting for the pump to complete its startup may be calculation based, but what is experienced in a facility processing inconsistent volumes at variable conditions can be quite different than these calculated rates and startup timings or shutdown ranges may need to be adjusted.

The amine unit has a significant impact on the stability of an AGI unit at a gas processing facility. If this unit has a design optimized strictly to design conditions the supply of and condition of acid gas entering the AGI train can be problematic during the startup period as flows may be low and quality poor. Even once amine operation is stabilized adequately, appropriately placed telemetry and control devices on the amine reflux condenser is critical to maintaining acid gas quality. Something as simple as ensuring temperature transmitters are placed as close to the cooler outlet as possible or adding positioners to control valves assemblies can make a significant difference to acid gas feed stability. Once volumes at PSGP were sufficient to operate both acid gas compression trains it became quite apparent that modifications to the original compressor loading philosophy were required to avoid significant operator intervention to manage loading oscillation. This prevented smooth transition anytime units were taken down or started before/after maintenance, leading to additional downtime and flaring. This was resolved at PSGP with the addition of a common suction line pressure transmitter and a Master PID loop and some logic for load sharing/unit selective control.

For sites like PSGP that produce their own power there is an additional startup complication of power stability. After 3 years in operation problems with power stability are infrequent to the point of non-existent, but at startup gas turbines are another piece of equipment that adds to the complexity of startup as there are operational and programming systems to streamline and troubleshoot. In our experience most of these challenges centered around communications between power generation and waste heat recovery, but whatever the cause, loss of power can have serious implications to an acid gas injection train and strategies around unplanned downtime for any reason, including loss of main power should be considered. Will any blowdowns be triggered in the AGI train? Is it possible that any area of the system could drop to temperatures where the acid gas is now over saturated? Is mitigation required if this does occur and what is the mitigation? Is there adequate redundancy/protection...

Produkt-Details

• Erscheint lt. Verlag: 24.2.2025
• Sprache: englisch
• Themenwelt: Technik ► Elektrotechnik / Energietechnik
• Themenwelt: Wirtschaft
• ISBN-10: 1-394-35627-7 / 1394356277
• ISBN-13: 978-1-394-35627-0 / 9781394356270