Comprehensive Oil and Gas Production Operations and Operations Guide: Gas Production Operations and Safety Standards and Operations and and Safety and Operations and Operations
Production Equipment and Processing Objectives
Production equipment must be designed and operated to achieve three fundamental processing goals during oil and gas operations. First, processed oil must reach a purity level of or higher, which corresponds to a Basic Sediment and Water (BS&W) content of less than or equal to at the point of sale. Second, natural gas must be treated to remove impurities and achieve a water vapor content of less than . Third, any processed water intended for discharge must comply with environmental standards, maintaining an oily waste and suspended particle content of equal to or less than as a monthly average.
Thermodynamics and Heat Recovery Systems
In gas compression systems, increasing the ratio of compression directly results in an increase in the temperature of the gas. To utilize this energy efficiently, a Waste Heat Recovery Unit (WHRU) may be employed. A WHRU is a specialized heat exchanger that captures heat from the hot exhaust gas stream of an internal combustion engine and transfers it to a working heat media. These systems typically incorporate auxiliary components such as pumps and expansion tanks. Additionally, the efficiency of plate heat exchangers is significantly enhanced by the large surface area provided by the plates themselves.
Methods of Separation and Fluid Dynamics
Separators are in-line pressure vessels equipped with specialized internal components designed to provide the necessary residence time for the separation of gas, oil, and water from reservoir or process streams. A Three-Phase vessel is specifically designed to separate gas from liquids, with the resulting gas and liquid streams being discharged independently. To facilitate the removal of liquids from gas, mist extractors, constructed from wire mesh or vanes, are utilized. Within hydrocyclone assemblies, centrifugal force is leveraged to enhance gravitational separation, allowing for the efficient partitioning of oil and water. Hydrocyclone efficiency is determined by liner cleanliness and the differential pressure across the system. Furthermore, hydrocyclone liners are designed for a primary specific amount of flow per tube.
Glycol Dehydration Processes
Efficient natural gas dehydration typically occurs at a desired operating temperature range of to . In the glycol dehydration process, sparge gas is utilized to strip additional water from the glycol. The process flow involves lean glycol from the glycol pump passing through a Gas/Glycol heat exchanger before entering the glycol contactor. To ensure maximum efficiency in the interaction between gas and glycol on offshore platforms, structured packing is preferred for the glycol contactor internal arrangement to mitigate the effects of platform motion. Additionally, a glycol separator is used to remove liquid hydrocarbons from the glycol stream before it enters the glycol reboiler.
Flow Assurance and Maintenance: Hydrates, Pigging, and Wax
The formation of hydrates in pipelines requires four specific elements: the presence of natural gas (such as methane), the presence of water, low temperature conditions, and high pressure. Other flow assurance challenges include the formation of emulsions, which are predominantly water-in-oil in producing operations and can be prevented by keeping produced fluids as warm as possible. Wax deposition can lead to increased fluid viscosity and may cause the crude to solidify in flowlines during extended shutdowns.
Pigging operations involve the use of "pigs" to perform maintenance without interrupting the flow within a pipeline. Pigs may become stuck due to several factors, including incorrect pig design or size, inappropriate pigging frequency, excessive wear of seals and cups, or unintentional pig bypass. In the Gulf of Mexico, under safety and environmental enforcement (SEE) requirements, subsea well production casing pressures must be documented on a daily basis.
Pump and Compressor Operations and Safety
Centrifugal pumps can be configured as single or multi-stage units and are capable of operating in either horizontal or vertical positions. Potential causes for low discharge pressure in these pumps include low suction pressure, low pump rotation, or excessive wear on the impeller. In contrast, positive displacement pumps are prone to extremely high pressures in blocked flow scenarios. To mitigate pressure waves caused by the reciprocating action of plungers in positive displacement pumps, pulsation dampeners are installed. It is also critical when switching well streams between manifolds that two different manifold valves are not open at the same time to prevent flow interruptions.
Safety instrumentation for gas compressors must include operable high-pressure (PSH), low-pressure (PSL), pressure safety (PSV), high-level (LSH), and low-level (LSL) sensors on the suction and each inter-stage scrubber. The PSH on the compressor suction, inter-stage scrubber, and final stage discharge should be set no higher than or , whichever is greater, above the highest pressure in the operating range. Furthermore, the PSH must be at least or , whichever is greater, below the activation pressure of the PSV.
Safety Integrity and Regulatory Compliance
Safety Integrity Level (SIL) is a metric used to quantify the reliability of safety functions. A SIL 2 device is characterized by a risk reduction factor ranging from greater than to less than . Pressure safety valves (PSVs) are mechanical devices designed to open during over-pressure events; the set pressure of a PSV must never exceed the Maximum Allowable Working Pressure (MAWP) of the protected vessel. For low-pressure vessels (operating at less than ), a "Big Joe" regulator may be used to maintain normal operating pressure. Safety devices like level bridles are often car-sealed open if they are regulatory devices, safety devices, or located in areas where they could be accidentally bumped.
Locked Valve and Isolation Protocols
Locked valves are categorized into two types. Type 1 locked valves prevent high-consequence safety or environmental events, and their movement is managed through operational movement protocols, personal isolation, or team leader approval. Type 2 locked valves are those that prevent lower consequence safety/environmental events or impacts on availability and production. For PSV suction and discharge valves, inspections must verify that P&IDs show the correct normal position, tags are fitted, and Pro-locks are in good condition. An operational movement supported by a Standard Operating Procedure (SOP) is required to open a valve with a Red Pro-Lock.
Workplace Safety and Shift Handover
Effective shift handovers at BP are governed by Procedure 500139 C04.5-0002 and consist of 8 essential elements. Section 6 of this procedure, "Operational Information," includes categories such as abnormal operations, alternate operating modes, and significant changes in unit operating modes during the shift. Before tasks begin, a Performing Authority (PA) must conduct a Tool Box Talk (TBT) at the worksite. The TBT should be clear, concise, and translated if English is not the workforce's first language. TBTs are required for the first task of the day, after breaks, and for each subsequent step of a project.
Safe operating and design limits must be reviewed every 5 years. Plant equipment must not be operated outside the safe operating envelope except for temporary operations covered by risk assessments, Management of Change (MoC), or temporary excursions permitted by engineering codes. For specific maintenance tasks, Level 2 SOPs require step-by-step sign-off by the end user and supervisor.
Leak Detection and Monitoring
Leaks and seeps are classified based on the substance and rate of release. A hydrocarbon release of from a pipe flange is classified as a C1-Hydrocarbon/Hazardous Utility Leak. For a produced water leak of on a pump seal, monitoring frequency is determined by a Risk Assessment. On offshore facilities, fire detection may be achieved via a fusible loop, where a loss of pressure triggers a fire detection signal. The maximum allowable leakage rate for a flowline FSV is a liquid flow of or a gas flow of .
Environmental Standards
The National Pollutant Discharge Elimination System (NPDES) in the US sets strict limits for oil and grease in produced water. The maximum monthly average is set at , while the maximum daily limit is . Crude oil API gravity is determined using a hydrometer, and the reading must be corrected based on the temperature of the oil sample.
Questions & Discussion
Question: A painter reports on the radio that their hand-held gas detector has alarmed. What actions do you take upon arriving in the area? Response: You must stop all hot work or spark-potential work in the area, notify the PTL, and identify the flowpath to depressurize the system. While confirming with a secondary detector is part of the process, immediate safety actions take precedence.
Question: What energy sources must be considered when designing an isolation for replacing a glycol circulation pump? Response: One must consider Electrical, Pressure, and Thermal energy sources.
Question: When flushing a K-Tek float-style level bridle, how do you mitigate the risk of crushing the float if both valves are closed and the float is at the bottom? Response: You should slowly open the upper valve to equalize pressure in the bridle before opening the lower valve.
Question: What setting is appropriate for PSH and PSL on a range chart if the high range is and the low range is ? Response: The settings are PSH and PSL .
Question: What is a Bowtie in the context of risk management? Response: A Bowtie is a qualitative risk management tool used to graphically communicate an event, its causes, consequences, and the barriers in place. It displays the relationship between risk events and barriers, helping to communicate complex risks to the workforce.