Acid Fracturing of a Gas Carbonate Reservoir: The Impact of Acid Type and Lithology on Fracture Half Length and Width

摘要

The Khuff formation is ideally made-up for acid fracturingbecause of the heterogeneous nature of the formation, whichtends to support the created fracture conductivity. Variousacid types were used to fracture this tight dolomitizedformation including: 28 wt% regular HCl, emulsified acid, andin-situ gelled acid. In addition, several wells were fracturedusing 15 wt% HCl/9wt% formic gelled acids. However, basedon production results and the large database of acid fracturetreatments (more than 70 wells); it appears that there is acorrelation between the acid type used and the lithology of theformation. An earlier study,1 which briefly examined thisphenomenon, indicated that the emulsified acid might be moresuited to low permeable zones. These low permeable rocksare predominately made up of limestone.Typically, changing the acid volumes, placementtechniques, or pumping rates, has optimized acid fracturetreatments by creating longer and wider fractures. However,we tend to ignore the effect of lithology in carbonateformations because we all believe that the rock interactionwith the acid is not as sensitive as in sandstone formations.With this large database of acid fracture treatments, acid rockinteractions were investigated to determine the relationshipbetween lithology and acid type.This work involves correlating the designed treatment tothe open-hole logs, core petro-physical data, analysis ofhundreds of samples collected following acid fracturetreatments, and production results.