A pressure drop within the wellbore of a well is both good and bad. The pressure drop between the reservoir and the wellbore that occurs at the perforations is the reason a well flows from the producing zone into the casing. However, anytime you have a pressure drop, you have a temperature drop and that can set up an environment where you begin to deposit iron sulfide and/or paraffin from the oil and precipitate scale deposits from the water. Not only does a well exhibit a pressure drop at the perforations but elsewhere in the casing. We will address that below and how the design of the Slimline® anchor can enhance well performance.
Causes of Pressure Drops in Oil Wells
A reduction in pressure within an oil well can be the result of a wide variety of issues. Some of those issues include:
- Reservoir Depletion: One of the primary causes of pressure drops in oil wells is reservoir depletion. Operators extract oil from the reservoir, which decreases its natural pressure over time. This natural depletion leads to a reduction in the driving force that pushes oil towards the surface. As a result, pressure in the well drops.
- Fluid Mobility: Fluid mobility is the ease with which fluids (oil, gas, and water) can flow through the reservoir rock. Operators need to carefully manage these fluids, or they can create pressure drops.
- Wellbore Damage: Damage to the wellbore itself can cause pressure drops. This damage may be a result of corrosion, scale buildup, or the intrusion of foreign materials into the well. Such obstructions can restrict the flow of fluids and reduce pressure.
- Temperature Variations: Changes in temperature within the reservoir and wellbore can affect fluid properties. When temperature drops occur, the viscosity of oil may increase. That increase makes it more challenging for the oil to flow, which can result in a pressure drop.
Impacts of Pressure Drops in Oil Wells
Monitoring and managing oil well pressure drops is important because those drops can have several negative impacts on production, including:
- Reduced Production Rates: The most immediate and noticeable impact of pressure drops in oil wells is reduced production rates. As the driving force behind fluid flow diminishes, the well’s ability to deliver oil to the surface is compromised. This can lead to decreased production and financial losses for operators.
- Increased Energy Costs: Operators many need to inject additional energy into the well to compensate for pressure drops. This often involves the use of pumps or compression systems, which can significantly increase operational costs.
- Reservoir Impairment: Excessive pressure drop within the reservoir can alter the relative permeability of the formation and can cause “water coning;” thereby reducing the production of oil through the reservoir and into the wellbore.
- Wellbore Damage: Corrosion and scale buildup, caused by changes in pressure and fluid composition, can potentially lead to costly repairs and safety hazards. In addition, scale, iron sulfide, and paraffin deposits initiated by the drop in pressure can plug the flow of oil into a pump or to the surface.
Unique Challenges with Sucker Rod Pump Systems
A tubing anchor catcher (TAC) secures the tubing string in deep wells that rely on a sucker rod pump (SRP) system for artificial lift. The TAC prevents unnecessary wear on the tubing string and the sucker rods. However, because the standard TAC can also restrict the flow of fluid through the annulus, it can create drops in pressure and temperature that can precipitate out scale, iron sulfide, paraffin and other sediment. With a standard TAC, that sediment can accumulate on top of the anchor and plant the entire string from being retrieved without an expensive workover.
Using the Slimline® TAC to Mitigate Pressure Drops
The patented Slimline® TAC from TechTAC® features a decreased diameter and tapered flow subs. That unique design increases flow-by capacity in the annulus by as much as 244% compared to other available TACs. This increased flow-by capacity reduces the flow regime from turbulent to a more laminar regime, thereby reducing those drops in pressure and temperature that can cause scale buildup and corrosion, which can grind production to a halt.
One senior completion foreman with a U.S.-based oil and gas company saw the the Slimline’s impact firsthand. “We have one well we used to call the ‘little stinker,’ because it had to be pulled every 3 months due to scale,” he said. “After installing a Slimline TAC, we didn’t need to pull it for 2 years.” For this organization and many other production companies, installing the Slimline TAC was a simple change that mitigated the pressure and temperature drops that could lead to downtime and expensive workovers.