1. What is the skin factor you would expect from a successful acidizing treatmen
ID: 118862 • Letter: 1
Question
1. What is the skin factor you would expect from a successful acidizing treatment and what acid would you use if the formation is
a. Carbonate
b. Sandstone
2. Why does fracturing improve productivity of wells?
3. True of false questions
a. Beam pumps may be used for high GOR (Gas Oil Ratio Wells)
b. Progressing cavity pumps are used for high viscosity oil reservoirs
c. Gas lift may be used for wells producing with high GOR
4. What the advantage of using jet pumps
Explanation / Answer
As per rule I can answer for 1st question only
The skin factor you would expect from a successful acidizing treatment :
The success can be measured in terms of Productivity Index (PI) improvement or skin reduction. An acid stimulation treatment can also cause further damage instead of damage removal. Precipitation products coming from the reaction itself or loose solids generated during the acidizing job might cause further plugging of flow channels. Dirt from the tank or tubulars, release of fines from carbonate rocks, precipitation of iron reaction products, plugging by colloidal sludge and chemical incompatibility of the acid system itself or with the formation might cause further problems. Some crude oils and strong inorganic acids can produce sludges such as organic deposits which cannot be dissolved. State of the art nowadays is the real-time-monitoring of an acidizing job. The skin factor correlated, for instance, with Paccaloni’s model from the measured pressure changes is plotted versus the injected volume of acid solution during the acidizing job in order to determine the optimum point when to stop the injection.
During the preparation of the acid solution minimize open air time while mixing the fluid batches.
Make sure the tanks and flowlines are clean.
A corrosion inhibition measure is to not produce the spent acid into the flowline after the acidizing job, but in tank. We can never be sure that 100% of the live acid totally reacted on the formation rock.
Oxide layers which may develop on the surface metallic components should be removed by pickling in order to avoid precipitations downhole.
Depending on the acid solution pumped, be aware that damage can also occur during shut-in time and not only during pumping and the primary reaction.
Carbonates
When doing carbonate acidizing we mostly use hydrochloric acid, HCl. The surface reaction rate of limestone with hydrochloric acid is very high which can cause wormholes even up to 10 feet long in the near wellbore region connected to the flow channels. Wormholes are caused by non-uniform dissolution of limestone, which basically means that larger pores grow faster than the smaller ones. The limiting factor in most of the cases is the mass transfer.
Example reactions:
CaCO3 + 2HCl –> CaCl2 + H2O + CO2
CaMg (CO3) 2 + 4HCl –> CaCl2 + MgCl2 + 2H2O + 2CO2
Standstone:
Most sandstone formations are composed of quartz particles, Si02, which are bonded together by various kinds of cementing materials, mainly carbonates, silica and clays. Both HCl and HF are used to dissolve these type of rocks. Mostly HF is used.
Example reactions:
Si02 + 6HF –> H2SiF6 + 2H20
Al2Si4010 (OH) 2 + 36HF –> 4H2SiF6 + 12H20 + 2H3AlF6
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