Page 251 - Petroleum Production Engineering, A Computer-Assisted Approach

Guo, Boyun / Computer Assited Petroleum Production Engg 0750682701_chap16 Final Proof page 249 21.12.2006 2:30pm

MATRIX ACIDIZING 16/249
Problems (b) the maximum expected surface injection pressure
at the maximum injection rate.
16.1 For the reaction between 20 wt% HCl solution and
calcite, calculate the gravimetric and volumetric dis- 16.6 A 40-ft thick, 20-md sandstone pay zone at a depth
solving power of the acid solution. of 8,000 ft is to be acidized with an acid solution
16.2 For the reaction between 20 wt% HCl solution and having a specific gravity of 1.07 and a viscosity of
dolomite, calculate the gravimetric and volumetric 1.5 cp down a 2-in. ID coil tubing. The formation
dissolving power of the acid solution. fracture gradient is 0.65 psi/ft. The wellbore radius is
16.3 A sandstone with a porosity of 0.18 containing 8 v% 0.328 ft. Assuming a reservoir pressure of 3,500 psia,
calcite is to be acidized with HF/HCl mixture solu- drainage area radius of 1,200 ft, and skin factor of 15,
tion. A preflush of 15 wt% HCl solution is to be calculate
injected ahead of the mixture to dissolve the carbon-
ate minerals and establish a low-pH environment. If (a) the maximum acid injection rate using a safety
the HCl preflush is to remove all carbonates in a margin of 400 psi.
region within 1.5 ft beyond a 0.328-ft-radius wellbore (b) the maximum expected surface injection pressure
before the HF/HCl stage enters the formation, what at the maximum injection rate.
minimum preflush volume is required in terms of
gallon per foot of pay zone? 16.7 A 20 wt% HCl is needed to propagate wormholes
16.4 A sandstone with a porosity of 0.15 containing 12 v% 2 ft from a 0.328-ft radius wellbore in a limestone
dolomite is to be acidized with HF/HCl mixture so- formation (specific gravity 2.71) with a porosity of
lution. A preflush of 15 wt% HCl solution is to be 0.12. The designed injection rate is 0.12 bbl/min-ft,
2
injected ahead of the mixture to dissolve the carbon- the diffusion coefficient is 10 9 m =sec, and the den-
3
ate minerals and establish a low-pH environment. If sity of the 20% HCl is 1:11 g=cm . In linear core
the HCl preflush is to remove all carbonates in a floods, 1.2 pore volume is needed for wormhole
region within 1.2 feet beyond a 0.328-ft-radius well- breakthrough at the end of the core. Calculate the
bore before the HF/HCl stage enters the formation, acid volume requirement using (a) Daccord’s model
what minimum preflush volume is required in terms and (b) the volumetric model.
of gallon per foot of pay zone? 16.8 A 25 wt% HCl is needed to propagate wormholes
16.5 A 30-ft thick, 40-md sandstone pay zone at a depth 3 ft from a 0.328-ft radius wellbore in a dolomite
of 9,000 ft is to be acidized with an acid solution having formation (specific gravity 2.87) with a porosity of
a specific gravity of 1.07 and a viscosity of 1.2 cp down 0.16. The designed injection rate is 0.15 bbl/min-ft,
2
a 2-in. ID coil tubing. The formation fracture gradient the diffusion coefficient is 10 9 m =sec, and the den-
3
is 0.7 psi/ft. The wellbore radius is 0.328 ft. Assuming sity of the 25% HCl is 1:15 g=cm . In linear core
a reservoir pressure of 4,000 psia, drainage area floods, 4 pore volumes is needed for wormhole
radius of 1,500 ft and skin factor of 10, calculate breakthrough at the end of the core. Calculate the
acid volume requirement using (a) Daccord’s model
(a) the maximum acid injection rate using safety and (b) the volumetric model.
margin 200 psi.