Abstract

Passive completions, comprised of inflow control devices and external packers, are usually considered in horizontal wells, located in risky or mature areas. These completions are proven techniques for reservoir conformance to mitigate water or gas-coning problems and ensure uniform production contributions along the horizontal section. After well completion or shortly after initial production, these wells may fail to sustain production, largely due to formation damage or plugging in the inflow control devices. The conventional acid program, applied on wells with non-passive completions, is not suitable on these wells, due to the risk of impacting the completion integrity to the extent that it will violate the installation purposes. The requirements of acid treating wells with the same completions become inevitable due to the increasing number of wells equipped with these completions in a major carbonate reservoir in Saudi Arabia. A smart approach has been developed through innovative thinking to stimulate wells equipped with passive completions. The new approach has successfully stimulated four wells and resulted in restoring well productivity. This smart stimulation approach demonstrates a competent method to clean out the ICD completion along the horizontal section and to remove formation damage.

This paper presents in depth discussion of rigless acid stimulation operations on oil producers to remove formation damage and improve well productivity, at a reduced cost. This paper also outlines the successful application of the smart approach in acid stimulation of horizontal wells — equipped with passive completion — and discussed the post-treatment results.

Background

Water injection was started to boost up and maintain the reservoir pressure. All producers were initially drilled as vertical producers and with the advancement of the water front, a great deal of the vertical producers were converted to short radius horizontals (SRH) that targeted the thin oil column behind the flood front.

The oil was sourced from Jurassic organic-rich lime mudstones, which were laid down in intershelf basins. The integrity of the thick anhydrite top seal is enhanced by the general absence of faults in the Jurassic section. The main oil reservoir is the Upper Jurassic Arab-D limestone, which improves upward from mudstone to skeletal-oolitic grainstone, reflecting successive upward-shoaling cycles. The excellent reservoir quality is due to the preservation of the primary porosity, the enhancement of permeability, and the presence of fractures in the deeper and tighter parts. The oil was sourced exclusively from Jurassic organic-rich mudstones and is effectively sealed beneath massive anhydrite. The general absence of faults at the Arab-D level maintained seal integrity.

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