Mud

How Does Formation Testing Work? While every effort is put forth before drilling begins to ensure a successful well, not every well hits hydrocarbons at a commercially productive level. Statistically, wildcat (or exploratory) wells have a one in seven chance of discovering oil or gas. While six may be dry holes, one in the group can make a big enough difference to outweigh all the risks. Once drilling operations have been completed, it is important for drillers, engineers and geologists to determine whether to move on to the next phase: completion for production. Formation tests ascertain if there are enough hydrocarbons to produce from a well, as well as provide important information to design the well completion and production facilities. Used to establish formation pressure, permeability, and reservoir and formation fluid characterization, there are three major methods of formation testing that help to reveal the downhole formation: well logging, core sampling and drill stem tests.

Elastomers have also been developed that will swell in the presence of water & water-based fluids. Swell is achieved by blending in a super absorbent polymer into the base elastomer compound. Once the packer is exposed to water, the water is absorbed by the polymer causing the packer volume to increase. This increase in volume corresponds to an increase in the packer diameter. Just like the oil-swellable elastomer, a seal is created once contact with the borehole wall is made. The water-swellable packer is capable of swelling in both monovalent and divalent cation brines. Using the super absorbent polymer creates a very stable water swell packer. If the water is removed and replaced with crude oil, the packer will maintain a seal. Recently a water-swellable elastomer has been designed and installed in heavy oil wells which use steam to heat up the reservoir to cause oil to flow. The high temperature water-swellable packer presently has an upper operational limit of 575°F (302°C).

Elastomers have also been developed that will swell in the presence of water & water-based fluids. Swell is achieved by blending in a super absorbent polymer into the base elastomer compound. Once the packer is exposed to water, the water is absorbed by the polymer causing the packer volume to increase. This increase in volume corresponds to an increase in the packer diameter. Just like the oil-swellable elastomer, a seal is created once contact with the borehole wall is made. The water-swellable packer is capable of swelling in both monovalent and divalent cation brines. Using the super absorbent polymer creates a very stable water swell packer. If the water is removed and replaced with crude oil, the packer will maintain a seal. Recently a water-swellable elastomer has been designed and installed in heavy oil wells which use steam to heat up the reservoir to cause oil to flow. The high temperature water-swellable packer presently has an upper operational limit of 575°F (302°C).

The picture above illustrates a FREECAP? I packer. The elastomer is wrapped on API pipe with weight, grade, and connection specified by the well design. The seal length is determined by the required differential pressure, the well temperature, and application. Solid metal end rings are secured to the base pipe and protect the elastomer while the completion is run to depth. Critical to the function of the end rings is that they create an extrusion barrier. As differential pressure is applied across the packer, forces are created that want to extrude the rubber in the direction of the applied pressure. The end rings support the elastomer which results in a hydraulic annular seal. Swellable packers can have pressure ratings as high as 10,000 psi. For low pressure applications there is a slip-on version of the swellable packer called a FREECAP? II. This packer works similar to a slip-on centralizer. They are often used to provide annular isolation for slotted liners, or flow barriers with sand screens which use inflow control devices.

the swell pressure increases until diffusion can no longer occur. At this point a differentially sealing annular barrier is created. Operationally, the benefit of a swellable packer is simplicity. There are no moving parts required to work, through pipe manipulation or by applied hydraulic pressure. No special service personnel are needed. The packers are simply run to depth, similar to the casing, and allowed to swell before production or injection operations begin. And allowed to swell before production or injection operations begin.