Cement Packer Installation in Highly Deviated Well Using the Balanced Hydrostatic Plug Concept through Coiled Tubing: Offshore Niger Delta

Abstract

The "balanced cement plug" concept has long been a standard industry practice for setting plugs in a wellbore. This requires setting a hydrostatic plug consisting of a column of brine, spacers, and cement slurry pumped into the annulus of a tubing/drillstring to create a balanced U-Tube that equates the hydrostatic head in the drillstring/tubing and annulus. Fluid volumes are calculated accounting for fluids both inside and outside the pipe at the given gradient, thus resulting in a hydrostatically "balanced system." Recently, this technology has been successfully deployed for cement packer design and execution using coiled tubing (CT) at a depth of 1,899 ft above the production packer with 111 bbl of calcium chloride brine existing (cement accelerator) below the tubing punch interval in the tubing-casing annulus. The cement packer installation design was for accessing bypassed hydrocarbon in high-angle (65 to 72º) deviated wells offshore the Niger Delta. Design considerations are reviewed and precautions for placement of high angle cement packer through CT are discussed. Initial designs to isolate the lower depleted zone were futile because of failed zonal isolation with mechanical plugs. Thus, an attempt to isolate the lower interval by pumping cement with 15% excess (openhole volume) led to having 17 bbl (1,899 ft) of cement within the 3.5-in. production tubing, and above the production packer. The CT deployed cement packer installation without a cement retainer presents unconventional solutions for placing cement at the height of 1,899 ft. The operation was successfully executed and the temperature log confirmed top of cement as proposed during the design phase. The holdup depth in the tubing was also tagged as expected with no cement U-tubing from the annulus. Post-job shut-in tubing and casing pressures, quantity of cement pumped, and flow testing have proven the success of the design and procedure implemented in challenging wellbores.