Abstract
Developing and producing a deep gas asset is a challenge because the reservoir is often of low permeability, commonly referred to as tight gas. In some cases, the wells are drilled under-balanced to prevent damaging the reservoir. Very often, it is necessary to drill through weak, depleted zones to reach the reservoir. These factors pose unique challenges to cementing materials used and methods applied. These challenges need to be understood in detail and solutions designed and implemented successfully for economical production of gas from deep environment.
Properties of cementing fluids, spacer and cement-slurry, should be optimized to enable successful cementing when the well is drilled under-balanced. The importance of properties such as fluid loss, density, and resistance to formation fluid influx are discussed and presented. Spacer fluids and cement-slurry need to be optimized based on reservoir parameters to help prevent fluid influx from the formation. The rate at which the slurry develops static gel strength is an important parameter to help prevent formation fluid such as gas from entering the annulus and either flow to other zones or come to the surface.
When drilling through depleted, weak zones the circulating and hydrostatic pressure should be minimized to help prevent losses to the formation. The density and rheology of the cementing fluids influence these values and should be optimized to help ensure successful placement of cement-slurry when there is a risk of losses. Design of the spacer fluid and cement-slurry to help prevent losses are discussed and presented. There are distinct advantages of using different chemical treatments ahead of the cement-slurry to control the losses. Different chemical treatment options will be presented and discussed.
The solutions discussed in this paper should help in constructing and operating the deep gas wells economically and safely.
