Abstract
Preventing unwanted migration of hydrocarbons has been an enduring challenge to the oil and gas industry. Regulations are in place to minimize the risk of leaking wells. However, future regulations are expected to become increasingly restrictive requiring operators to minimize the risks of potentially unwanted hydrocarbon migration during the well planning stage.
Hydrocarbon flows may originate from pay zones, or from non-commercial hydrocarbon-bearing formations. Some of the most hazardous gas flows have originated from unrecognized gas behind conductor, surface or intermediate casing. Often determining the precise source of annular flow is difficult.
There are numerous short-term solutions aimed at preventing the flow of hydrocarbons including optimizing stand-off, fluid placement, slurry design and mechanical methods. These techniques relate to working with the cement slurry in its liquid state prior to curing, and are aimed at preventing undesirable movement of hydrocarbons within the cemented annulus before the cement has set. However their effectiveness is lost once the cement has set, making it vulnerable to hydrocarbon migration should cement sheath damage occur.
The paper describes a unique isolation solution based on a responsive cement system with intrinsic self-healing properties automatically activated upon hydrocarbon exposure. Activation occurs whenever the integrity of the cement sheath is compromised, e.g. cracks and microannulus, and then efficiently seals the leak path by a swelling mechanism. The solution rapidly forms a complete hydraulic barrier by healing damage, and continues to re-seal should further damage occur. The technical advantages of this solution are shown, illustrated through successful field tests.
