Artificial Lift

In the Permian Basin, new unconventional wells on ESP systems experience production challenges due to high gas to liquid ratio. Unconventional wells having high initial rates with steep declines requires wells to be pumped aggressively early on. ESP’s by nature are designed to pump only liquids. Gas entering the ESP not only decreases volumetric efficiencies, but also causes high temperature issues and erratic run behavior. This decreases production and degrades the mechanical integrity of the ESP, leading to higher maintenance costs and ESP failure.

This paper will cover the theory of operation of downhole sucker rod pumps, compression ratio calculations, some misconceptions about gas handling, simple special valves and accessories, complex specialty valves, gas breakout in the pump, dual compression and specialty pumps, some successful industry solutions, and other ideas about dealing with gas in downhole sucker rod pumps.  

Downhole separation of gas and solids for sucker rod pumping continues to be a significant challenge, particularly in horizontal wells. An advancement in downhole separation has been achieved by realizing there was an opportunity to intentionally take advantage of transient multiphase flow conditions where liquids and solids flow reversals exist. Multiple case studies in this presentation, demonstrate that taking advantage of multiphase flow reversals can enhance downhole separation performance and capacity, while at the same time lower operational risk.

 Horizontal wells have a tendency to have surges of fluid and gas when producing. Especially in the case of gas, we tend to see gas production flowing in slugs, resulting in intermittent production of liquid and gas. This unpredictability of gas slugs and surges leads to free gas entering the pump more frequently and being harder to control than in a vertical well. This can lead to decreased production, efficiency, and pump fillage. To deal with the issues that surging in horizontal wells can lead too, Odessa Separator has developed the surge valve.

More efficient operations and lower failure rates will result if sucker rod lifted wells are operated with a pump filled with liquid.  Dynamometer and fluid level surveys can be used to identify when the well is operating properly and when there are operating problems.  There are a variety of recommended practices for operating sucker rod lifted wells to provide low operating cost and low failure rate.  Data will show that long and slow versus short and fast both result in high failure rates when the sucker rod pumping system has incomplete pump fillage.

Review of Field Data To Evaluate Impact on Overall Maintenance Costs when Rod String Spacing Tool/Rod Rotator is implemented with a Wireless POC Load Cell As companies seek to optimize performance of rod pumped wells, they examine common problems which may include improper rod string spacing resulting in rod pump damage, rod failures and cable failures of pump off control (POC) wired load cells. Traditional methods of adjusting rod strings requires removal of rod clamps and exposes field personnel to pinch, fall and struck-by hazards.

In the reciprocating rod lift system, the sucker rods are subjected to cyclic stresses during service which accumulate leading to fatigue failures. It is well known that the shot peen process increases the fatigue life on metal parts; with respect to sucker rods several manufacturers claim to have implemented shot peening in their manufacturing process for years. To achieve optimal parameters which yield a dramatic increase in fatigue life requires extensive studies on both input parameters and comparative fatigue testing.

In sucker rod pumps, accurate downhole data is necessary for control and optimization of wells and assets. Downhole data is calculated from data measured at the surface. 

Unconventional wells are drilled in shale formations to produce oil and gas utilizing horizontal drilling and hydraulic fracturing. Many think fracturing creates a ‘rubble zone’ around the wellbore allowing the free oil and gas to be produced. 

Deviated wellbores, whether intentional or unintentionally drilled, are becoming ever more common. Rod-on-tubing friction occurs as a result of these wellbore deviations. This friction has a detrimental effect on the longevity of the equipment through accelerated mechanical wear. Downhole friction can also obscure analysis and optimization as the friction distorts the calculated downhole conditions. The only methodology currently available to account for this wellbore friction is through by way of a wellbore deviation survey.