Expandable sand screens (ESS®.) are a relatively new sand control system, which combines many of the properties of gravel packs with the ease of installation of a stand-alone screen.Although they have been used in a wide variety of applications, they are not considered a panacea and have an operational envelope, which is becoming clearer with time.
Weatherford's ESS system currently (June 2005) has 340 installations and over 700 years of combined production.A recent survey of the installations was analyzed in terms of performance and reliability.
The productivity performance of the ESS has been shown to be very good, with an average skin of 0.3 being achieved in recent openhole applications.ESS completions generally perform better than the baseline models.Where field comparisons were possible, they also performed better than alternative sand control completions.
Over the 340 ESS wells, ESS has a reliability comparable with other sand control systems, with initial failures less than 5% and a production failure rate of 0.021 failures/well.year.This gives a projected survival rate at 20 years of greater than 90%.This rate is expected to get better with improving operations, designs, systems and application selection.
When the first ESS was launched in 1999 it was a radical departure from convention, it introduced the concept of direct screen contact with the formation as a means of increasing productivity, sand control and reliability.
ESS was designed and aimed specifically at openhole applications, despite the subsequent use of it in cased-hole applications. Features such as large exposed filter area and variable ESS borehole contact (becoming known as compliant expansion) were included to provide gravel pack functionality with the operational simplicity of a stand-alone screen.ESS has been used to replace openhole gravel packs (OHGP), cased hole gravel packs (CHGP), cased hole frac and packs (CHFP) and standalone screens (SAS).
The design premise was that a compliantly expanded filter that could eliminate as much of the annular gap as was practicable would also promote rapid formation stabilization and minimize the movement of sand particles around the screen during initial transient sand production period. The large directly exposed filter surface was designed to minimize the pressure drops in the screen and sand pack composite caused by mud particles and formation fines. Both features were aimed at improving productivity and reliability of the sand-face completion. The role of the reduction in the annular gap in increasing completion reliability has been discussed in Helland et al.
With 340 ESS installations and 65 km now installed, the statistics are becoming significant and it is now possible with confidence to determine whether ESS does indeed offer the improvements claimed by the designers and to formulate selection criteria for their use. This paper presents data on performance of ESS completions together with data on long-term reliability and failure rates.The ESS application selection process is used to show how failure rates can be reduced and long-term reliability improved.
There have been a large number of case studies published which have looked at ESS performance, in a wide variety of well types, vertical, horizontal, gas, gas-condensate, water and oil wells.The current maximum fluid production rate is 25,000 bpd, the maximum gas rate is 290 MMscf/d, and the maximum water injection rate is 40,000 bwpd.Some specific published examples are given below.
Weekse et aldocumented the installation and performance of three long horizontal gas wells in the Brigantine field, in the Southern North Sea.The wells had up to 40% improved production over expectation.They were completed 32 days ahead of schedule with a saving of $13.5M.These wells have been producing for over 4 ½ years.
The performance of the ESS completed wells in the gas condensate Scoter Field was also very good with no evidence of mechanical skin or formation damage. These wells have been producing for over two years.