I came across two fascinating SPE papers (SPE 219536 and SPE 219552) that delved into the economic performance and operational efficiency of gas lift systems versus ESP in unconventional horizontal fracked wells. If you're interested in gas lift or hunting for an alternative artificial lift system, these papers are a must-read!
Although gas lift hasn't yet strutted its stuff in the Coal Seam Gas (CSG) industry, it offers some compelling advantages over the incumbents like PCP and RRP. This could be especially crucial as the industry ventures into uncharted territories with horizontal drilling and fracking in less productive areas. Here's what caught my eyes:
- Handles multiphase flow and solids like a champ! (because most hate a clogged pump as much as a coffee machined clogged with too many grounds)
- Greater MTTF with less frequent intervention, not only reducing workover costs but also reducing production impairment risks and improving ultimate recovery (fewer workovers = less sleepless nights with workover rig calls or with the workover budget)
- Scalability benefits through central compression and gas lift distribution networks, enabling economic expansion (think of it as the Amazon Prime of artificial lift – centralize and distribute!)
Recently, I facilitated an internal technical session on Gas Lift, exploring its design intricacies and operational considerations for petroleum engineers, particularly in the context of CSG industry. Some key highlights are:
- Debunking common misconceptions: Gas lift doesn't rely on critical velocity as conventional gas wells do. It achieves lifting efficiency without reaching friction-dominated critical velocities. Also, contrary to popular belief, gas lift doesn't increase FBHP – in fact, gas lift demand/pressure must be progressively reduced to optimise FBHP. (Yes, I'm that person at parties who says "Actually..." – but in this case, it matters!)
- Subsurface understanding is critical. Reservoir deliverability and significant water-gas ratio changes through different production phases are required to properly design and operate/optimise gas lift. Every gas lift should start here (much like how I can't start my day without understanding my coffee-to-water ratio).
- As George Box wisely said, "All models are wrong, but some are useful." Designing gas lift with limited relevant data can be intimidating – like trying to bake a cake with half the recipe missing. My advice for any modeling work: start with problem framing. What do you need to understand about gas lift operability given reservoir depletion and flow rate variability, particularly with pilots?
- Effective unloading is crucial—careful pressure and flow assurance management during start-up greatly impacts gas lift success. Even if the static fluid level is below surface, the new level when pushing fluid between conduits represents the true kick-off pressure needed for compression system design. Have you considered slug management? If you normally use gas pressure to dump liquid, how would you manage during the unloading phase without gas production? And let's not forget about hydrate – the unwanted houseguest of production operations!
Have you considered gas lift in challenging CSG fields? I'd love to hear your experiences and insights – especially if they involve fewer workover rigs and more production!
