Issue link: http://yearbook.epmag.com/i/671218
ARTIFICIAL LIFT TECHBOOK: CASE STUDY 40 | May 2016 | hartenergy.com I t is common practice in many high initial rate horizontal wells in deep unconventional plays to transition through multiple artifcial lift systems. Historically, operators attempt to minimize operat- ing costs by transitioning to rod pumping as soon as possible. However, rod pumping often cannot bridge the gap from natural fow; therefore, a phase of gas lift is today's norm. Multiple lift systems re- quire several planned workovers over the life of the well while challenging producing characteristics increase the necessity for unplanned workovers. As a result, per barrel capex and opex over the life of the well are higher than desired. The lifting gap How to combine systems and effectively switch sys- tems while producing the most oil at the lowest cost per barrel is not a simple task for the produc- tion engineer. Sometimes the technical envelopes and capabilities of the lowest-cost artifcial lift sys- tems overlap and sometimes they do not, leaving a "lifting gap." Maximizing production rate often requires a higher-cost, intermediate-stage artifcial lift system like gas lift to fll this lifting gap. This results in a typical strategy of natural fow, followed by gas lift, and fnally rod pumping for the remain- ing economic life. Natural fow Natural fow occurs when the reservoir pressure exceeds the total pressure loss through the wellbore from the reservoir level to surface, both hydrostatic and frictional, plus any pressure applied at surface. This can occur when a well is initially brought on production and will terminate when neither of the following conditions are met: • Normally or overpressured reservoirs where the full hydrostatic column of the reservoir fuids exerts a pressure that is less than the reservoir pressure. • Suffcient gas production that the fuid veloc- ities and multiphase fow regimes in the well- bore are adequate (above the critical rate) to transport produced liquids to surface. Rod pumping Rod pumping is industry proven as cost effective and reliable. Under ideal conditions, rod pumps are highly effcient over a broad operating envelope of production rates and depths. However, they are challenged by gas interference, solids production, the extreme depths of today's unconventional plays and the extra load caused by placing the pump in the deviated section of the wellbore. In practice, these problems limit the rod pumping operating window of rod pumping, thus opening up a lifting gap. A new system combines the benefts of gas lift, multiphase fow conditioning practices, research, feld testing and operator experience to close the lifting gap. The Artifcial Lift Gap By Camille Jensen, Dave Kimery and Jeff Saponja Production Plus Energy Services Inc. Sometimes the technical en- velopes and capabilities of the lowest-cost artifcial lift systems overlap and sometimes they do not, leaving a "lifting gap."