Accurate fluid placement had always been a challenge in depleted reservoirs. Criticality of such jobs multiplies when cement plug is to be placed in a depleted reservoir or when there is a marginal tolerance in terms of volume or differential pressures for the placement of cement plug. Various techniques are used in industry to spot specific cement slurry volume in stages to get accuracy in plug depth. Bailers being most successful, demerits from having very less volume of cement slurry which can be placed, resulting in multiple runs. To effectively place fix quantity of chemical plug or cement slurry in a well, a coiled tubing conveyed hydrostatic valve (fluid retainer) can be successfully deployed, by placing known quantity of liquid only.
In depleted oil and gas wells (especially the ones in secondary recovery phase) there is a static sump present. Reservoir shut off solutions cannot be used in this scenario as the increase in hydrostatic head causes loss of the pill into the the reservoir zone. In such scenarios, cement plugs are preferred to be dumped using dump bailer, however, for volumes larger than 1 bbl bailer option is not feasible. Hydraulics balance is crucial to job success, and such applications virtues the use of a coiled tubing conveyed Hydrostatic Valve.
This paper discusses operation of hydrostatic valve and present case studies of two wells in Pakistan, where this technology is effectually implemented together with acid soluble and salt saturated cement slurry.