| dc.description.abstract | Well stimulation techniques are applied on a regular basis to enhance
productivity and maximize recovery in oil and gas wells. Among these techniques,
matrix acidizing is probably the most widely performed job because of its relative low
cost, compared to hydraulic fracturing, and suitability to both generate extra production
capacity and to restore original productivity in damaged wells. The acidizing process
leads to increased economic reserves, improving the ultimate recovery in both
sandstone and carbonate reservoirs.
Matrix acidizing consists of injecting an acid solution into the formation, at a
pressure below the fracture pressure to dissolve some of the minerals present in the rock
with the primary objective of removing damage near the wellbore, hence restoring the
natural permeability and greatly improving well productivity. Reservoir heterogeneity
plays a significant role in the success of acidizing treatments because of its influence on
damage removal mechanisms, and is strongly related to dissolution pattern of the matrix.
The standard acid treatments are HCl mixtures to dissolve carbonate minerals and HCl-
HF formulations to attack those plugging minerals, mainly silicates (clays and feldspars).
A matrix acidizing apparatus for conducting linear core flooding was built and
the operational procedure for safe, easy, and comprehensive use of the equipment was
detailed. It was capable of reproducing different conditions regarding flow rate, pressure,
and temperature. Extensive preliminary experiments were carried out on core samples of
both Berea sandstone and Cream Chalk carbonate to evaluate the effect of rock
heterogeneities and treatment conditions on acidizing mechanisms. The results obtained from the experiments showed that the temperature activates
the reaction rate of HF-HCl acid mixtures in sandstone acidizing. The use of higher
concentrations of HF, particularly at high temperatures, may cause deconsolidation of
the matrix adversely affecting the final stimulation results. It was also seen that the
higher the flow rate the better the permeability response, until certain optimal flow rates
are reached which appears to be 30 ml/min for Berea sandstone. Highly permeable and
macroscopic channels were created when acidizing limestone cores with HCl 15%. In
carbonate rocks, there is an optimum acid injection rate at which the dominant wormhole
system is formed. | en |
