Salvage of Casing Leak Wells on Artificial Lift in a Mature Oil Field

Abstract

Abstract The Bahrain oilfield, discovered in 1932, is one of the most mature fields still under active exploitation in the Arabian Gulf. Around 750 wells have been drilled in the field and it is worth mentioning that even today the discovery well in the field is also under active service as a gas injector after several salvages. Over the years starting from the discovery year the well design has evolved from the initial 6 casing string completions to the present simplified 2 casing string completions for the 12 vertically stacked Bahrain Zones from the Mishrifs occurring at 1600 ft. to the Kharaib zone occurring at depths of around 3200 ft. The prevalence of a very highly permeable shallow aquifer has made it very difficult to obtain effective isolation by cementing of the surface casing to surface. In addition, the high salinity and corrosivity of the water in this aquifer has lead to casing leaks is several earlier generation wells. This has in a few cases lead to underground blow outs from the high pressure producing zones into the aquifer and in some instance even surface gas seepages. In this paper, we shall be presenting an update of the history of casing leak occurrences in the field and the various innovative methods adopted to abandon self flowing high pressure zones and then salvage these wells in low pressure non-self flowing zones. The low pressure zones are completed on artificial lift either on pump or gas lift after isolating the leak zone with a concentric string and packers as necessary. In a way, it can also be said that, these salvaged wells have enabled us to test, evaluate and produce the otherwise economically unviable low pressure, low productivity zones. To summarize the paper will dwell on the reasons for casing leak occurrence, evolution of the well design to minimize casing leak and optimize well costs, abandonment of high pressure self flowing zones in the casing leak wells and finally the re completion of these wells on artificial lift in non self flowing low pressure zones.