Factors Contributing to SAGD Start-Up Performance

Abstract

SAGD start-up has considerations for both well integrity and warm-up efficiency. Interest in using insulated tubing to address issues related to both considerations is evolving. The scope of this work is to demonstrate how start-up performance is affected by the use of tubing insulation, both in terms of well integrity and reservoir warming efficiency. Both of these considerations are sensitive to operational and reservoir factors that are specific to the implementation. The basis for using insulated tubing for start-up insulation should therefore take those factors into consideration. This paper demonstrates the use of wellbore thermo-hydraulics modelling to determine the sensitivity of primary metrics of well integrity and SAGD start-up efficiency to the configuration of tubing, insulation, reservoir injectivity, and various thermal characteristics of casing, cement and formations. The wellbore thermo-hydraulics model includes heat transfer across tubing and casing, between fluid conduits and into the formation. Furthermore, it incorporates a convective heat transfer model to take into account fluid injection association with partial or full "bull-heading" into the reservoir. Boundary conditions allow injection rates to be ramped up consistent with field operations, and and the model calculates the pressure ramp-up associated with the transient mass flow rate applied to the well. The results include a comprehensive description of the transient temperature in the casing, corresponding to the applied mass injection transient. This information can be used for well integrity interpretations, and start-up rates can be evaluated to manage the risk associated with start-up. Furthermore, the injection temperature and steam quality distribution in the tubing strings and tubing/liner annulus can be determined over the start-up period and during the circulation phase as a basis for determining circulation duration required to reach conditions for SAGD start-up. Temperature distributions in the reservoir can also be determined at prescribed distances from the wellbore.

Application of Temperature Fall-Off Interpretation Method in Superheavy Oil or Oil Sand SAGD Process

“…Besides, based on Fourier's law of thermal conduction, the equation of the heating rate under steady thermal conduction is 5 Geofluids…”

“…For superheavy oil or oil sand SAGD projects, the preheating stage is usually indispensable to form interwell hydraulic connection or mobile oil before conversion to the normal SAGD process [2]. The preheating ways usually include steam circulation, steam bullheading, and steam stimulation [3][4][5]. Affected by strong reservoir heterogeneity, shale interlayers or laminae, thief zones (e.g., bottom water, top water, and gas cap), and undulating well trajectory, there are great differences in both preheating time (usually 3-6 months) and steam consumption (usually 25,000-50,000 m 3 ) among different well pairs [6].…”