Page 9 - Offshore Well Construction

CHAPTER 5
Cementing
Petroleum Extension-The University of Texas at Austin

OBJECTIVES
Primary Cementing

• Isolation of casing shoe
• Isolation of production zones—prevent cross-flow between intervals at different pressures
• Protection of water zones—prevent drilling fluid contamination of aquifers
• Isolation of problem interval – extreme losses, well control, side tracking
• Protection of casing—from corrosive formation fluids; e.g., H S, CO 2
2
• Casing support—e.g., support for conductor (load bearing—bending moments derived from supporting
BOP/tree/riser and potential snag loads from fishing activities), prevent thermal buckling

Secondary or Remedial Cementing

Additional cementing done at a later stage; e.g., sealing off perforations, top up job on conductor, repair casing leaks,
squeeze casing shoe, setting plugs, etc.

PLANNING
Planning for a cement job consists of evaluating a number of features, including:

• Assessment of hole conditions (hole cleaning, size, washouts, temperature)
• Mud properties
• Slurry design
• Slurry placement
• Additional equipment (float equipment, centralizers, ECPs)

COMMON CEMENTING PROBLEMS
Common problems that affect all cement jobs include:
• Poor hole condition (doglegs, borehole stability, washouts, hole fill, cuttings beds, etc.)
• Poor mud condition (high gel strengths and yield point, high fluid loss, thick filter cake, high solids content,
lost circulation material, mud/cement incompatibility)
• Poor centralization (cement not placed uniformly around the casing, leaving mud in place)
• Lost circulation
• Abnormal pressure
• Subnormal pressure
• High temperature

CEMENT TYPES
API defines 9 different classes of cement (A to H) depending on the ratio of the four fundamental chemical components
(C S, C S, C A, C AF where C = calcium, S = silicate, A = aluminate, and F = fluoride).
3
2
3
4
5.1