Technology Focus: Well Stimulation (June 2010)

Abstract

Technology Focus Reviewing the numerous papers for this feature showed that the primary theme worldwide, throughout the last approximately 18 months, has been acidizing carbonate formations. Fine tuning this information, it is further seen that the primary interest was zone isolation or diversion. Fracture acidizing seems to be on everyone’s mind as well. Certainly, acidizing sandstones is an important area, but only approximately 15% of the papers were related to sandstone acidizing; thus, with limited space, the emphasis here is on carbonates. Too often, when multiple zones are to be acidized, mechanical isolation is not feasible and chemicals and/or particulate materials are used for diversion. Post-treatment production logging and results often indicate inadequate stimulation of the target zones. When matrix acidizing carbonates, there are many treatment options from which to choose. Choices relate to amount and type of acid per unit of zone, injection rates, heating the acid (cool dolomites), fluid-loss-control materials, diverting materials, as well as the many other additives including friction reducers, corrosion inhibitors, surfactants, iron control, and on and on. Many of the additives are necessary, but of utmost importance is getting the proper amount of acid into each zone. A primary issue with fracture acidizing is obtaining conductivity and length, with the decision being which is more important, conductivity or length. In most cases, it is not possible to have both (i.e., long conductive length), particularly in high-temperature situations. In a low-permeability situation, length becomes more important than conductivity, and the requirements may be met more easily with an inert fluid and proppant. In a high-permeability situation, conductivity becomes more important than length, more easily met with acid. Production-increase predictions can help sort out the required balance between length and conductivity. The following summaries provide insight into acidizing carbonates. Well Stimulation additional reading available at OnePetro: www.onepetro.org IPTC 13203 • “Case Study of Successful Matrix Stimulation of High-Water-Cut Wells in Dubai Offshore Fields” by F. Shnaib, SPE, Dubai Petroleum, et al. SPE 128043 • “Stimulation of Multilayered High-Carbonate-Content Sandstone Formations in West Africa Using Chelant-Based Fluids and Mechanical Diversion” by M. Parkinson, SPE, Chevron, et al. SPE 127768 • “Acid/Scale-Inhibitor Stimulation Treatment for High-Temperature Cased-Hole Frac-Pack Subsea Wells: Fluid Qualification and Formation-Damage Assessment” by M. Marquez, Chevron, et al.