Reaction Rate and Fluid Loss: The Keys to Wormhole Initiation and Propagation in Carbonate Acidizing

Abstract

Reaction Rate and Fluid Loss: The Keys to Wormhole Initiation and Propagation in Carbonate Acidizing T. Huang; T. Huang U. of Texas at Austin Search for other works by this author on: This Site Google Scholar A.D. Hill; A.D. Hill U. of Texas at Austin Search for other works by this author on: This Site Google Scholar R.S. Schechter R.S. Schechter U. of Texas at Austin Search for other works by this author on: This Site Google Scholar Paper presented at the International Symposium on Oilfield Chemistry, Houston, Texas, February 1997. Paper Number: SPE-37312-MS https://doi.org/10.2118/37312-MS Published: February 18 1997 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Get Permissions Search Site Citation Huang, T., Hill, A.D., and R.S. Schechter. "Reaction Rate and Fluid Loss: The Keys to Wormhole Initiation and Propagation in Carbonate Acidizing." Paper presented at the International Symposium on Oilfield Chemistry, Houston, Texas, February 1997. doi: https://doi.org/10.2118/37312-MS Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentAll ProceedingsSociety of Petroleum Engineers (SPE)SPE International Conference on Oilfield Chemistry Search Advanced Search AbstractThe efficiency of the matrix acidizing process in carbonates depends strongly on the wormholing phenomenon - if worm holes are formed, the effects of near wellbore damage can be overcome with relatively small volumes of acid. Numerous previous studies have shown that worm hole patterns can be placed in these general categories:compact dissolution in which most of the acid is spent near the rock face;the wormholing pattern; anduniform dissolution in which many pores are enlarged, as typically occurs in sandstone acidizingWe have developed a theory of the wormholing process which predicts when the wormholing pattern is most efficiently created as a function of the acid flux and other treatment variables.By testing this theory with several independent sets of laboratory data, we can now demonstrate the important roles that surface reaction rate and fluid loss play in the wormholing process. This theory accurately predicts the optimal flux (that which leads to dominant wormholes with a minimum of branching and hence a minimum acid volume) for experiments with HCl in limestone and dolomite at several temperatures and with acetic acid in limestone. Surface reaction rate differs by several orders of magnitude in these experiments and is the only process variable that differs greatly among them. Paradoxically, though worm holes are formed because the overall reaction rate is controlled by mass transfer in the wormholes, diffusion rates play only a minor role in the wormholing process.Fluid loss through the walls of the wormholes ultimately limits the distance to which worm holes can propagate. Because of this effect, laboratory linear core floods will give optimistic predictions of worm hole penetration distances. We developed a cylindrical flow model to represent the flow field around a worm hole propagating from a wellbore which illustrates how to translate laboratory results to field conditions.We have used these theories to predict optimal acid formulations and injection rates for field conditions. In general, the lower the reaction rate (such as at low temperatures in dolomites or with weak acids in limestones), the lower the injection rate required, making it easier to propagate dominant wormholes under matrix treating conditions in the field.IntroductionNumerous studies of the wormholing process in carbonate acidizing have shown that the dissolution pattern created can be characterized as being one of three types:compact dissolution in which most of the acid is spent near the rock face;the wormholing pattern; anduniform dissolution in which many pores are enlarged, as typically occurs in sandstone acidizing.These studies have also shown that the acidizing process is most efficient (defined as the process that will enhance near-wellbore permeability to the greatest depth with the smallest volume of acid) when the wormholing pattern develops. A third observation common to these studies is that the pattern created depends on acid flux, with the compact pattern created at relatively low acid flux, the worm hole pattern developing at intermediate flux, and the uniform pattern at high flux. Of course, there is not an abrupt transition from one pattern to another. As acid flux is increased, the compact pattern will change to one in which large diameter worm holes are created; further increases in flux yield narrower wormholes which propagate farther for a given volume of acid injection; and finally, as acid flux is increased more, the worm holes become more and more branched until ultimately the uniform pattern is observed.P. 775^ Keywords: drilling fluid property, drilling fluid formulation, reaction rate, drilling fluids and materials, Upstream Oil & Gas, drilling fluid selection and formulation, acidizing, fluid loss, drilling fluid chemistry, Wormhole Initiation Subjects: Pressure Management, Drilling Fluids and Materials, Unconventional and Complex Reservoirs, Well control, Drilling fluid management & disposal, Acidizing, Carbonate reservoirs, Well Operations, Optimization and Stimulation This content is only available via PDF. 1997. Society of Petroleum Engineers You can access this article if you purchase or spend a download.