Natural gas extraction is a complex process that involves navigating various geological, engineering, and operational challenges. Even when wells boast sufficient reservoir pressure, porosity, and permeability within surrounding sand formations, several common problems can hinder gas flow.
Understanding these common challenges becomes paramount for a sustainable and optimized future in energy production. Experts at CNPS offer insights into some common natural gas well production problems.
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Declining Well Productivity
One of the most prevalent issues in natural gas well production is the decline in well productivity over time. This decline is often a result of reservoir depletion, where the natural gas reservoir loses pressure as the gas is extracted. Additionally, factors such as water intrusion and solid deposition in the wellbore can contribute to reduced productivity.
To combat declining productivity, operators implement various strategies. Enhanced oil and gas recovery techniques, such as hydraulic fracturing and nitrogen injection, can help maintain or increase reservoir pressure. Regular well maintenance and the use of corrosion inhibitors also play a crucial role in preventing wellbore issues.
Gas Flow Restriction through Casing Perforations
Natural gas well production encounters a critical challenge when gas flow through casing perforations is restricted, primarily due to the accumulation of sand. Perforation blockage or sand production is a multifaceted problem stemming from various causes.
Wellhead Choke Opening
The issue may arise when the wellhead choke opening is excessively large, allowing sand particles to enter the production stream.
Extended Well Shut-In Periods
Prolonged well shut-ins can lead to suspended sand settling at the bottom, causing blockages in the perforations.
Mechanical Formation Breakdown
Mechanical formation breakdown or collapse can result in the production of formation sand “clumps” or individual grains along the produced fluids.
Gravel Pack Failure
In cases of gravel pack completion, gravel pack failure can contribute to sand production issues.
Siliceous or Clay Fines
Formations containing clay or siliceous fines may produce these particles with hydrocarbons, causing plugging in both the wellbore and reservoir.
To investigate and confirm whether sand is obstructing the perforations, a weighted wireline is descended through the tubing. If the wireline loses tension, indicating a “tagged bottom,” the depth is compared to a record of well completion to tally the perforations covered by sand. If 20% to 30% of perforations are covered, well washing with a coil tubing unit is recommended.
Sand production can have several adverse effects, including sand erosion resulting from the solids, especially when combined with high velocity. This erosion ensues in pipework, tubing, and turbulence, such as elbows, chokes, and diameter restriction zones.
Additionally, the production loss is a consequence of sand control equipment installation, as it decreases production rates because of the pressure drop across the unit. With a production 0.1% rate, the produced sand disposal becomes a concern, generating a notable amount of solids per unit of production.
To overcome the challenges posed by sand production, various techniques and methods are employed both at the surface and at the bottom hole. Gravel packing systems are commonly used at the bottom hole to control sand.
Three purpose-built types of sand removal units by Schlumberger are utilized at the surface during well testing: the sand separator, dual-pot sand filter, and cyclonic desander. These technologies aim to mitigate the adverse effects of sand production, ensuring the smooth and efficient extraction of hydrocarbons from natural gas wells.
Liquid Loading of Production Tubing with Condensate or Water
Liquid loading of production tubing represents another significant obstacle in natural gas well production, particularly in mature wells or those experiencing declining reservoir pressure.
Liquid-related challenges in gas wells can manifest in various forms, with the presence of an aquifer beneath the gas zone potentially leading to water encroachment or coning. This becomes particularly pertinent when the well completion type is open hole, as liquids may originate from other zones.
The liquids produced alongside gas may include free water inherent in the formation, and the entry of hydrocarbon vapor and water into the well can result in condensation during the ascent up the production tubing, emerging as a liquid.
Identifying the source of these liquids is crucial for effective problem resolution. Water coning may occur when a high gas rate “sucks” water from a zone below the perforated zone.
Alternatively, pressure sustenance from a water zone can cause the water to “travel” to the perforations. Liquids may also come from another zone, or they may be free-formation water originating from the same zone as the gas.
Furthermore, condensation, influenced by temperature decreases or pressure increases, can occur higher in the well, causing water to fall back and accumulate at the perforations.
Several factors influence the phenomenon of liquid loading, including surface pressure, tubing size, and the volume of liquids produced with the gas. Recognizing liquid loading is vital over the life of a gas well, as liquid production tends to increase while gas production decreases. This can lead to the accumulation of liquids in the wellbore, impacting well performance and potentially causing reservoir damage if unnoticed.
To overcome these challenges, various strategies can be employed. Plunger lift systems utilize well shut-in pressure buildups to lift fluid columns out of the well efficiently without venting. Well shutting allows the bottom hole pressure to increase, subsequently venting the well to the atmosphere (well blowdown) is another approach.
Velocity tubing installation, well swabbing to get rid of accumulated fluids, and incorporating artificial lift systems are additional solutions. Moreover, the use of foaming agents can assist in mitigating the effects of liquid loading, ensuring the continued productivity and efficiency of natural gas wells.
The incorporation of advanced monitoring tools, such as echometer devices and memory gauges, further aids in the early detection and management of liquid-related issues, minimizing potential losses and safeguarding the integrity of gas wells over their operational lifespan.
Back Pressure on Wellhead
The critical issue can impede gas flow even in wells with sufficient reservoir pressure, porosity, and permeability. This problem arises from inadequate infrastructure for gas transportation and processing, regulatory constraints on production rates, and insufficient capacity in surface facilities.
The effects of back pressure are far-reaching. Reduced gas flow rates are a direct consequence, as back pressure resists the natural flow of gas, leading to diminished production rates.
Prolonged exposure to back pressure can result in damage to the wellbore and surrounding reservoir, further complicating the operational landscape. Additionally, back pressure interferes with maintaining the ideal pressure conditions for efficient gas extraction, presenting challenges in reservoir management.
Addressing back pressure requires a strategic approach. Upgrading surface facilities to handle increased production rates is crucial. Collaboration with regulatory bodies to address constraints and find mutually beneficial solutions is essential for sustainable operations.
Moreover, implementing advanced wellhead and compression technologies can effectively manage and mitigate back pressure, ensuring optimal gas flow conditions.
Gas Hydrates Formation
Gas hydrates, ice-like solids formed by the combination of natural gas and water under specific pressure and temperature conditions, can obstruct wellbores and pipelines. Hydrate formation is a significant concern, particularly in offshore wells and subsea pipelines.
Insulation and heating systems are used to prevent hydrate formation in pipelines. In some cases, chemical inhibitors are injected into the well to inhibit hydrate formation. Researchers are continually exploring innovative methods to mitigate hydrate-related issues, such as the development of hydrate inhibitors.
Formation Damage
During drilling and well completion, various substances, including drilling fluids and formation damage during the drilling process, can hinder the natural flow of gas from the reservoir to the wellbore.
Acidizing and hydraulic fracturing are common techniques employed to remove formation damage and enhance wellbore permeability. Reservoir stimulation methods are applied to increase the productivity of the well by improving fluid flow.
Corrosion
Corrosion is a pervasive issue in the oil and gas industry, including natural gas well production. Corrosive elements in the produced fluids, combined with environmental factors, can lead to the degradation of wellbore equipment and infrastructure.
The use of corrosion-resistant materials, regular inspection, and the application of corrosion inhibitors are essential to mitigate corrosion. Additionally, proper coating and cathodic protection systems used by CNPS help extend the lifespan of wellbore equipment.
All cutting-edge oilfield equipment and solutions by CNPS redefine industry standards, ensuring optimal performance and safety. From advanced drilling technologies to state-of-the-art production equipment, we are your trusted partner in enhancing operational excellence.
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