Shale oil and gas production has significantly helped secure this leadership position since 2012. The downside of shale oil & gas production are the rapid decline rates for the producing wells.In a World Oil article, Accelerated production improves shale well economics, Emerson’s Al Majek and Terry Cox teamed with Experitec‘s Gene Little and Southwestern Energy‘s Josh Jolly and Teo Baughn to share how to improve the management of the free-flow cycle of gas by applying well automation.
…known as Extended Annular Flow (EAF)…, initial production is through both casing ports, enabling the well to produce at higher rates than through the tubing alone. During this period, which can last several months, rental equipment, as well as additional supervision, is required.
The authors described an alternate method, casing flow management, which is based on:
…controlling flow from one port of the casing, to obtain an effect similar to using EAF during the entirety of the well’s free-flowing lifecycle phase.
This is accomplished by installing:
…a tubing bypass line with an automated valve, under the control of a Remote Terminal Unit (RTU). All equipment is mounted, to facilitate easy removal at a point in the freeflow phase, determined by the operator.
Southwestern Energy [hyperlink added]:
…selected the Emerson FloBoss series of flow computer controllers. Completing the package meant supplying enclosures, a solar power system, choke, actuator and customized programming. Experitec, Inc., a process control equipment and instrumentation company, provided the final integrated solution.
The casing flowrate:
…is controlled by the Control RTU via a PID (proportional integral-derivative) loop. The set point is calculated by the unit for a value approximating 50% of the critical flowrate.
This critical flowrate:
…indicates the minimum rate of flow from the well, to lift liquids out of the wellbore. Flow at less than critical velocity allows water to collect in the well, eventually curtailing production.
The authors explain that it is desirable to operate the casing below the critical flowrate and the tubing above it. The PID loop will begin to close the casing choke if the tubing flow rate drops below the critical rate. For their control strategy, there is also:
…an override, based upon time. The casing choke is shut in completely between 5 a.m. and 6 a.m., each day, to build up the casing pressure and increase the subsequent tubing flowrate. This helps clear the wellbore of any accumulated liquids or sand.
By applying this casing flow management control strategy:
…the sales rate increases to around 2.773 MMscfd. The incremental production over the tubing flow mode is 555,000 scfd, approximately 25% more than the previous sales rate.
From a project cost standpoint, the:
…cost per well reduces with a greater number of wells per pad, due to the sharing of the RTU system between the wells. Even with the most-expensive single-well version, project payout falls easily within a 30-day period.
The authors conclude:
The revenue reduction, resulting from early deployment of casing flow management, is more than compensated by eliminating the additional EAF expenses.
The casing flow management system has now become the preferred choice from the start of operations.
Read the article for more on the flow calculations used, control strategy, field results and overall economic benefits.