Chapter V Primary Cementing

Two plug method: Cementing head Bottom plug – hollow Top Plug - solid

Portland cement powder & Water Slurry = Also called Neat cement Shallow well 24-36 hrs WOC WOC = Waiting on Cement

Type C Cement Portland – is a finer grind Avg. diameter is smaller. Reduces WOC ~ 1/2

By 1968 Class A – Neat Cement B - Sulfate resistant C - Shorter WOC D - 6000 – 10,000 ft E - 10,000 – 14,000 ft F - 10,000 – 14,000 ft with good sulfate resistance

Basic Cement - 8000 ft Class G Good sulfate resistance Class H - 8000 ft Moderate sulfate resistance Being phased out

Accelerators - CaCl2 NaCl

Retarders Calcium Lignosulfonate

Lightweight additives Most cement slurries 15 -17 lbs/gal Drilling mud 9.5 lb/gal - 15.6 lb/gal Hydrostatic head (HH) at 4000 ft HH (mud) = 9.5 x 0.052 = 0.494 psi/ft 0.494 psi/ft x 4000 ft = 1,976 psi HH (cement) = 15.6 x 0.052 = 0.8112 psi/ft 0.8112 psi/ft x 4000 ft = 3,245 psi

Heavyweight Additives (16 - 20 lb/gal) Hematite (iron ore) Barite Lost circulation additives Gilsonite Cellophane flakes Walnut Hulls

Salt additives - NaCl Optimum typically 18% salt 1.) Improve bonding in shale 2.) Dispersing agent 3.) Causes cement to expand as it sets Optimum typically 18% salt

Slurry Design Pumpable until your finished P & T both increase with depth P ~ 0.433 psi/ft T ~ 2 °F/ft Depth (ft) Temp (°F) 5,000 174 10,000 274

Viscosity Type G = 5 gal water/sack TOO viscous to pump Optimum: Maximum strength at 2.8 gal water/sack TOO viscous to pump Optimum: Type G = 5 gal water/sack

Strength - Composition - Age (28 days) - Temp > 230 F reduces strength

WOC determined by time to reach 80 -100 psi tensile Strength = adequate → 8-10 psi tensile strength Compressive ~ 8 - 10x tensile WOC determined by time to reach 80 -100 psi tensile

Volume & Density (MATH!) Cement measured in "sacks" 1 sack = 94 lb = 1 cu ft dry powder 1 cu ft cement = 0.478 cement 0.522 void space

Slurry yield - cu ft/sack Slurry weight - lb/gal Slurry yield - cu ft/sack Example - Class G Absolute volume of water = 8.33 lb/gal Water = 0.12 gal/lb Cement = 0.0382 gal/lb

Volume per sack for Class G Water = 0.12 gal/lb Cement = 0.0382 gal/lb Volume per sack for Class G 94 lb x 0.0382 gal/lb = 3.59 gal/sack Volume of cement 3.59 gal/sack Volume of water + 5 gal Total volume slurry = 8.6 gal

Slurry yield =? Slurry density = 135.65 lb = 15.8 lb/gal 8.59 gal Weight of water = 5 gal x 8.33 lb/gal = 41.65 lb Slurry 135.65 lb 8.59 gal Cement 94 lb 3.59 gal Water 41.65 lb 5 gal Slurry density = 135.65 lb = 15.8 lb/gal 8.59 gal Slurry yield =?

Conversion factor: cu ft → gal 7.48 gal/cu ft Slurry yield: 8.59 gal/sack = 1.15 cu ft/sack 7.48 gal/cu ft

7” 8.75” Class G = 8.59 gal/sack Hole = 8.75" diameter OD casing = 7" Area= OD casing = 7" 1500 ft deep Area= 8.75” 7” Area= Area= 60.13 - 38 Area= 21.65 sq. in. Area= 0.15 sq ft

amount of 225.5 cu ft slurry needed = 1.15 cu ft / sack = 196 sacks Volume = 0.15 sq ft x 1500 ft = 225 cu ft amount of slurry needed 225.5 cu ft 1.15 cu ft / sack = = 196 sacks

Safety factor Engineering Margin Surface casing - 100% (400 sacks) Intermediate casing - 50 - 75% Production casing - 25% Can't run out !

Placement Techniques Mud & cement are: Non-Newtonian fluids laminar flow

Non-Newtonian laminar flow "gel" critical velocity bonding of casing

Solutions: Achieve bonding 1.) Clean casing 2.) Condition the mud. 3.) Pre-flush 4) Use centralizers 5.) Use scratchers 6.) Flow rate high enough for turbulent flow 7.) Sufficient contact time turbulent flow

260 linear ft/min "rule of thumb" 0.15 cu ft / ft × 260 ft/min 39 cu ft/min = 33.9 sacks/min 1.1 cu ft / sack 39 cu ft/min x 7.48 gal / cu ft = 291.7 GPM