by Dr. Franklin Foster, 2006
[note: this article made possible by support and funding from the Petroleum Society of CIM, Lloydminster Section]
The trend in SAGD production is toward lower pressure steam injection. This approach lowers operational costs and improves recovery rates. However, low pressure SAGD requires an artificial lift system (ALS) in order to optimize production rates. The challenge is compounded because SAGD conditions are too severe for rod or PCP (progressing cavity pumps) pumping systems.
These severe conditions may include:
Downhole temperatures in excess of 200° C
Production rates varying from over 1000 m3/d to under 100 m3/d
More than 15% of produced water flashing into steam during lift
Need for production efficiency at low intake pressures
System able to handle a wide range of fluid viscosity
System able to produce solids
System able to operate in cold temperature surface conditions
Need for low capital and operating expenditures (CAPEX and OPEX)
Currently in testing to see if it can handle these conditions is a technology which has been around in the oil patch before - the Hydraulic Gas Pump (HGP). This technology uses high-pressure gas to positively displace production fluids. Additional benefits come from the ability of the HGP to use on site field gas as both the power source and the injection gas. Additional benefits result from the HGP having good tolerance for produced solids, partly due to it having very few moving parts.
At a recent field test well, the HGP showed impressive results. The horizontal injection bore was at a depth of 528 m and the production well bore average temperature was 145° C. Using a cycle of 30 seconds injection and 50 seconds venting, the well achieved a steady state production rate of 150 m3/d. In fact, the timing of the cycling components appears to be a crucial parameter in achieving optimum operating conditions and production rates. In short, all testing to date indicates the HGP may well be an excellent choice when providing an ALS to a low pressure SAGD scenario.