Evaluation of In-Situ Generated Acids for Filter-Cake Cleanup

Abstract

Evaluation of In-Situ Generated Acids for Filter Cake Clean Up Hisham A. Nasr-El-Din; Hisham A. Nasr-El-Din Saudi Aramco Search for other works by this author on: This Site Google Scholar Abdullah Mohammad Al Moajil Abdullah Mohammad Al Moajil King Fahd University of Petroleum & Minerals Search for other works by this author on: This Site Google Scholar Paper presented at the European Formation Damage Conference, Scheveningen, The Netherlands, May 2007. Paper Number: SPE-107537-MS https://doi.org/10.2118/107537-MS Published: May 30 2007 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Get Permissions Search Site Citation Nasr-El-Din, Hisham A., and Abdullah Mohammad Al Moajil. "Evaluation of In-Situ Generated Acids for Filter Cake Clean Up." Paper presented at the European Formation Damage Conference, Scheveningen, The Netherlands, May 2007. doi: https://doi.org/10.2118/107537-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 European Formation Damage Conference and Exhibition Search Advanced Search AbstractFilter cake removal is a difficult task, especially in horizontal and extended reach wells. Water-based drilling fluids consist of xanthan gum as a viscosifier, starch as a fluid-loss control, sized calcium carbonate or salt particles to increase the mud density. Conventional chemical means used to remove filter cake are reactive mineral acids, enzymes, chelating agents, oxidizers, or combinations of these chemicals. Controlling of the reaction rate of the cleaning fluids with the filter cake material is an essential factor that determines the efficiency of filter cake removal.This study assesses the performance of three acid precursors (esters) that produce organic acids. These precursors produce low-molecular weight organic acids that can dissolve calcium carbonate particles from the filter cake. The rate of hydrolysis of acid precursors can be adjusted to produce a predetermine acid concentration at bottom hole conditions. Enzymes, mainly a-amylase, can be added to these esters to break starch that is present in the filter cake. The slow release of these weak organic acids ensures proper and efficient removal of the filter cake.Lab studies using static HPHT filter press indicated that the three systems can remove the filter cake efficiently. The rate of hydrolysis was measured for each system, and found to be a function of temperature and type and concentration of the acid precursor. Surface tension measurements conducted for solutions of the three precursors at different temperatures highlighted low surface tension values for the spent acids, which are needed to lift the spent acid following the treatment.No phase separation or precipitation was observed when the three systems were heated at temperatures up to 250°F. Surface tension measurements indicated that the formic acid system had low surface tension, which will accelerate lifting these fluids from tight formations. Acetic and lactic acid systems had much higher surface tension, and a suitable surfactant will be needed to reduce the surface tension. The kinetic study indicated the very rapid reaction rate of the precursor of formic acid and a moderate reaction rate in the acetic acid system. The reaction rate of the precursor of lactic acid was in between the two systems and more close to the in-situ acetic acid system.HPHT experiments showed that formic acid system was very efficient at short soaking times at temperatures of 200 and 250°F. The performance of lactic acid was comparable to formic acid when the soaking time was increased from 4 to 6.75 hrs. The efficiency of acetic acid was much lower than the other two acids. Acetic acid will require much longer soaking times.IntroductionDrilling horizontal/multilateral wells is utilized to enhance both hydrocarbon recovery and total well productivity from many types of reservoirs.1,2 Drilling, workover and production operations may result in near-wellbore formation damage that in most cases cannot be prevented e.g. Pore plugging by calcium carbonate particles from drilling fluid, drilled solid particles, or particles from the formation.3The level of the near-wellbore formation damage caused by drilling fluids depends on the drilling fluid characteristics, formation properties, and operating conditions (e.g., shear rate, overbalance pressure, temperature, and solids loading).4Long horizontal and multi-lateral wells are tended to be complex which increases the challenge in cleanup techniques.5,6 This is mostly because the length of the target zone complicates cleaning the filter cake uniformly.7 Thus, it is important to clean drill-in fluid damage effectively to reach the aim of uniform removal from the entire completion interval.8Current approaches introduced to remove filter cake include the use of live acids, strongly buffered organic acids,9 chelating agents, oxidizing agents,10 enzymes,7,11,12 in-situ organic acids, or combinations of these chemicals.13Delayed release organic acids overcomes the problems and limitations associated with the conventional chemicals means used to break the filter cake namely, high reactivity of live acids, enzymes and oxidizer attack specific polymers and does not dissolve calcium carbonate particles, the deposition of iron (III) oxide by oxidizers, and the difficulty to retard the reaction rate at high temperature for chelating agents.14,15 Keywords: drilling fluids and materials, Upstream Oil & Gas, acid system, drilling fluid selection and formulation, drilling operation, organic acid, acid concentration, drilling fluid property, drilling fluid formulation, concentration Subjects: Drilling Operations, Drilling Fluids and Materials, Directional drilling, Drilling fluid selection and formulation (chemistry, properties) This content is only available via PDF. 2007. 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