- Mud Engineering
- Waste management
- Drilling & Completion
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The casing is run, lowered down the hole to ensure the stability of the well, is slightly smaller in diameter than the well so that it could be cemented onto the wall of the well. The cement in injected into the casing pipe and pressured so it comes up from behind the casing and solidifies in few hours. A type of cement used for this purpose is known as Portland cement, which is adapted for bottom hole temperature and pressure.
There are two types of cementing job:
Primary Cementing, where a separating adjuncture known as spacer is used to displace the cement, overlying the mud, from inside the well to behind the casing where the cement sets. This could take about 12 to 24 hours hours in normal operations, depending also on the length of the well section to be cemented.
Secondary cementing is necessary for long casing section, and where there is a weak formation leading to a non-properly cementing job from Primary Cementing. In that case there might be a need to do a “top up” or secondary cementing. Cement is injected directly from behind the casing to fill up outstanding section. In extreme case the casing may be pieced (though rarely) so as to fill in the inefficiently cemented regions during primary cementing.
How do we know if the cementing is good or not? There are two common log types used in assessing the efficiency of a cementing job. Examples of these are:
The cement evaluation logs work on the basis of a standard calibration based on empty casing. Then any increase of amplitude to the right imply poor casing and to the left good casing. The principle is that good casing reduces the amount of waves that get to the receptors after reflection, so increased attenuation implies good cement job. On the VDL you see the weak signals implying good contact with wall.
This refers to the ability to make a well depart from it’s vertical downward penetration and and control its direction horizontally or near horizontal below the surface. It is achieved by using a wedge object that evdiates the tracjectory of the well. One of such object is known as a whip stack (see figure below).
Today directional drilling has advanced and change of direction (using a mud moto for example) and the calculation and application of desired trajectory is achieved through advanced techniques. More on this on the section on Geosteering.
Well completion and stimulation
Well completion involves preparing a well for produciton or injection. The aim of stimulating a well is to reduce skin effect and enhance hydrocarbon flow into the well; this is achieved by chemical enhancement such as use of acid or mechanical process such as reservoir fracturing. This skin factor results from the damage occurring near the well bore during and after drilling, and most likely inhibiting flow to a certain degree.
An adapted acid such as HCL (for carbonate rock) or HFL for (tight sandstone) in the chemical process, but this are not without their downside since acid can be a major hazard to both man and the environment.
Fracturing is achieved by a mix of proppant gel and beads which may remain in the cracks to maintain the open fractures and flow. Reservoir fracturing requires a prior study and understanding of the stress regime of the formation, to avoid fractures in unexpected direction which can lead to major pressure hazards.
Mud or fluid Engineering is an important aspect of the drilling, as the drilling fluid mixture must be very well weighted to be just above the pore pressure of the formation, to avoid a kick. Sometimes there is need to weight the mud but also to give it a viscous nature so that it does not allow formation fluid to flow into the well. Where a fracture is suspected and there is a tendency to lose the fluid into the formation, a fracture attack (frac attack) pills are injected into the well through the mud.
A mud drilling report will cover Drilling Fluids properties, conditioning of active system to maintain mud properties as per program, and any preparation of more or less volume of kill mud (using Barite and Calcium Carbonate for example). The amount of additives received and their mixing are recorded daily. The Drilling Activities are recorded with pumped High Viscosity (Hi-Vis) or Low Viscosity (Low-Vis) pills or tandem pill, every given number stands drilled and. These pills are used to circulate hole clean.
WASTE MANAGEMENT and TRANSPORTATION are vital aspects required both technology and logistics.