Acid Fracturing Treatment in an Iranian Carbonated Reservoir
- Abdolnabi Hashemi (North Drilling Company)
- Document ID
- World Petroleum Congress
- 21st World Petroleum Congress, 15-19 June, Moscow, Russia
- Publication Date
- Document Type
- Conference Paper
- 2014. World Petroleum Council
- 3 in the last 30 days
- 89 since 2007
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Acid fracturing is a sensitive stimulation technique that has been widely used by the oil industry, but it is limited to so many considerations. An acid fracturing treatment must produce a conductive flow channel long enough to alter the flow pattern in the reservoir from a radial pattern to one that approaches linear flow. This needs a high rate of acid flow completed with formation solution in acid.
Considering the above restrictions imposed by acid fracturing, its applicability is limited to special cases where no better solution is available especially in Iranian oil fields. In this paper, one of these special cases is studied occurred in a carbonate reservoir in Iran. This was the first successful acid fracturing operation in an Iranian reservoir which makes the condition so delicate and unique as there was so many uncertainties and lack of experience.
As we know, hydraulic fracturing has been used worldwide in damaged formations and formations with low conductivity but performing acid fracturing has been limited to so many operational and reservoir restriction. The main difference between acid fracturing and proppant fracturing is the way fracture conductivity is created. In proppant fracturing, a propping agent is used to prop open the fracture after the treatment is completed , . In acid fracturing, acid is used to etch channels in the rock that comprise the walls of the fracture. Thus, the rock has to be partially soluble in acid, so that channels can be etched in the fracture walls .
As such, the application of acid fracturing is confined to carbonate reservoirs and should never be used to stimulate sandstone, shale, or coal-seam reservoirs. Long etched fractures are difficult to obtain, because of high leakoff and rapid acid reaction with the formation .
Two major problems of acid fracturing are fracture closure and fracture plugging. Fracture closure occurs in the absence of proppant in high pressure reservoirs. So, acid fracturing is usually limited to low pressure and shallow reservoirs.
On the other hand, in some formations, regular or high strength acid fracturing may not provide sustainable production increase if large quantities of fines are released in the fracturing by the acid treatment, thus blocking the fracture. Also high strength acid may over-etch some very soluble carbonates, resulting the crushing of the pillars and post after the fracturing pressure is released or at the later date when the reservoir pressure declines. Thus, the fracture would close, blocking linear flow paths to the wellbore. So, for successful acid fracturing operation formation must be studied .
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