Polished Bore Receptacle
Optimal production rates in heavy oil wells are being achieved using new technically advanced completion tools and production systems. Some of these advanced systems may involve steam injection or solvent injection into the formations. The most instrumental advance of these, are the introduction of heat (steam) to lower the viscosity of the heavy oil, and allow it to be pumped to surface. The introduction of this heat to the components of a completed wellbore will affect the normal functioning of the material makeup of this equipment. The largest effect of heat to this equipment is the expansion and contraction of materials (steel, rubber), causing dimensional changes. These changes result in equipment malfunctions and equipment failures down hole.
One of the most common failures of down hole equipment, due to heat expansion and contraction, is with the casing liner hangers and packer type seals. As the production liner (ie; slotted liner in horizontal section) expands due to heat, the liner has a tendency to grow upwards. The top of this production liner is held in place by a casing hanger, located at the bottom of the intermediate casing of the well. As the liner grows (under a head of steam), the elements (rubber seals) of the liner hangers fail and cause steam bypass at the heel of the well, effecting the uniform steam distribution to the formation.
By placing a Polished Bore Receptacle (PBR) directly above the float equipment in the intermediate casing string, a properly designed casing liner hanger (Flow Control Hanger-FCH) can be positioned inside this PBR to allow production casing movement without having a steam breach past the FCH. The PBR is designed to have a tight tolerance honed inside diameter to match to the FCH’s outside diameter of its steel seals. The PBR is equipped with a “no-go” at the bottom of the receptacle. This smallest honed inside diameter of the PBR does not allow the FCH to pass through the PBR and aids in easy installment.
A specific gas nitrating process is applied to the PBR during manufacturing, which creates a hardened and non-corrosion finish to the i.d. of the PBR. This process is impregnated into the PBR material and does not affect diameter tolerances or separate during thermal material movements. The hardness allows for drilling tools to pass or rotate through the PBR without damaging the i.d. sealing surface of the PBR, during drilling of the horizontal section.